Download pdf - PLTB Gas - Technical · PDF filePLTB Gas iv Gas Pipeline Hydraulics..... 47 Steel Pipe - Design & Stress Analysis ... Cathodic Protection Attenuation Calculation ..... 162 Polyethylene

PLTB Gas

iii

Table of Contents

How to Export or Save Reports in Other Applications? ................................................................. 1

How to Export Report in Adobe Acrobat? ................................................................................. 1

How to Export Report to Microsoft Word? ................................................................................ 4

How to Export Report in Microsoft Outlook Express? .............................................................. 6

Gas Properties Calculations ............................................................................................................ 9

Gas Mixture Properties Calculations .......................................................................................... 9

Pipeline Facilities .......................................................................................................................... 11

Orifice Meters ........................................................................................................................... 12

Relief Valves: Reaction Force in an Open Discharge System .................................................. 19

Pipeline Compressors.................................................................................................................... 23

Centrifugal Compressor - Adiabatic Head ................................................................................ 23

Centrifugal Compressor - Required Adiabatic Horsepower ..................................................... 25

Centrifugal Compressor - Required Polytropic Horsepower .................................................... 27

Centrifugal Compressor - Fan Laws ......................................................................................... 29

Reciprocating Compressors - Capacity and Horsepower ......................................................... 30

Discharge Temperature ............................................................................................................. 33

Compressor Station Piping - Diameter and Gas Velocity ........................................................ 34

Local Atmospheric Pressure ..................................................................................................... 35

Accidental Gas Releases and Pipeline Rupture ............................................................................ 37

Accidental Gas Release through a Small Hole from Pressurized Gas Pipeline ........................ 37

Accidental Gas Release Rate from a Full-Bore Pipeline Rupture ............................................ 40

Natural Gas Pipeline Rupture - Depth, Radius, & Width of Crater .......................................... 43

PLTB Gas

iv

Gas Pipeline Hydraulics ................................................................................................................ 47

Steel Pipe - Design & Stress Analysis .......................................................................................... 57

Restrained Gas Pipeline - Stress Analysis ................................................................................ 59

Unrestrained Gas Pipeline Stress Analysis - Steel Pipe............................................................ 61

Flume Design ............................................................................................................................ 67

Natural Gas Pipeline Rupture - Depth, Radius, & Width of Crater .......................................... 79

Maximum Impact Load and Penetration Depth ........................................................................ 82

Pipeline Anchor Force Analysis ............................................................................................... 84

API - 1117 Movement of In-Service Pipelines ......................................................................... 86

Pipe Requirements for Horizontally Drilled Installation .......................................................... 90

Buoyancy Analysis and Concrete Coating Thickness .............................................................. 92

Buoyancy Analysis and Concrete Weights Spacing ................................................................. 94

Steel Pipeline Crossings .............................................................................................................. 105

API 1102 - PC PISCES ........................................................................................................... 105

Wheel Load Analysis .............................................................................................................. 123

Track Load Analysis ............................................................................................................... 130

Design of Uncased Pipeline Crossings ................................................................................... 137

Pipeline Testing & Miscellaneous .............................................................................................. 139

API 1104 - Appendix A: Weld Imperfection Assessment ...................................................... 139

API 1104 - Appendix A: Weld Imperfection Assessment ...................................................... 140

NiSource Blowdown Calculations .......................................................................................... 142

Pipeline Corrosion ...................................................................................................................... 147

Cathodic Protection ..................................................................................................................... 155

Table of Contents

v

Cathodic Protection Attenuation Calculation ......................................................................... 162

Polyethylene Pipe Design and Pipeline Crossings...................................................................... 165

Dead Load on PE Pipe - Prism, Marston and Combined Load .............................................. 165

Spangler's Modified Iowa Formula for PE Pipe ..................................................................... 167

Modulus of Soil Reaction (E') - Average Values for Iowa Formula ...................................... 168

Modulus of Soil Reaction (E') - Values of E' for Pipe Embedment ....................................... 169

Values of E'n Native Soil Modules of Soil Reaction .............................................................. 170

Soil Support Factor (Fs) .......................................................................................................... 171

Pipe Wall Compressive Stress (PE Pipe Crushing) ................................................................ 172

Distributed Static Surcharge Load Directly over Buried PE Pipe .......................................... 173

Distributed Static Surcharge Load not over Buried PE Pipe .................................................. 177

Live Load: Aircraft Load on Buried PE Pipe ......................................................................... 181

Index ........................................................................................................................................... 185

1

How to Export or Save Reports in Other

Applications?

How to Export Report in Adobe Acrobat?

Requirements: In order to export report to Adobe Acrobat, version 5.0 or 6.0 of Adobe

Acrobat must be installed on your computer.

1. On the report toolbar

select and click on the “Print…” button.

2. On the printer selection screen select Adobe PDF (or Adobe Distiller) and click

“Print” button

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3. After you click “Print” button you will be prompted to save the file. Select the

directory/folder, rename the file and click “Save” button.

How to Export or Save Reports in Other Applications?

3

Technical Toolboxes, Inc.

PLTB Gas

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How to Export Report to Microsoft Word?

Requirements: In order to export report to Microsoft Word or any other COM application

such as Visio, the application must be installed on your computer.


select and click on the “Copy” button.

2. Minimize application, open MS Word select “Edit” and then click “Paste”

Note: If report has more then one page, report should be exported page by page, to scroll

through pages use following


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The imported report may need some additional editing.


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How to Export Report in Microsoft Outlook Express?

Requirements: In order to export report to your email client such as Microsoft Outlook

Express, the email software must be installed on your computer.


select and click on the “Copy” button.

2. Minimize application, open MS Outlook Express (or any other email client) select

“Edit” and then click “Paste”


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Note: If report has more then one page, report should be exported page by page, to scroll

through pages use following

buttons on the report toolbar.

The imported report may need some additional editing.


9

Gas Properties Calculations

Gas Mixture Properties Calculations

This module is based on the calculation procedures contained in the following documents:

- GPA Standard 2172, " Calculation of Gross Heating Value, Relative Density and

Compressibility Factor for Natural Gas Mixtures from Compositional Analysis."

- A.G.A . Transmission Measurement Committee Report No. 8

- API MPMS 14.2


11

Pipeline Facilities

Regulator Station Sizing

Sizing of regulator is performed using Universal Gas Equation :

1. For Subsonic Flow

2. For Sonic Flow equation is reduced to:


12

Orifice Meters

This module is developed in accordance with A.G.A. "Orifice Metering of Natural Gas and

Other Related Hydrocarbons "( A.G.A. Report No. 3 ). The results of the calculations fully

comply required number precision and rounding.


Pipeline Facilities

13

Hot Tap Sizing

Scope:

When a compressible fluid, such as natural gas or air, is passed through an orifice, the rate of

flow is determined by the area of the orifice opening; the absolute upstream pressure is P1; and

the absolute downstream pressure is P2: unless the ratio P2/P1 equals or is less than the critical

ratio. When P2/P1 equals or is less than the critical ratio downstream pressure no longer effects

rate of flow through the orifice, and flow velocity at the vene contracta is equal to the speed of

sound in that fluid under that set of condition. This is commonly referred to as critical or sonic

flow. Orifice equations are therefore classified as "sonic" or "subsonic" equations.

1. 0 Critical Ratio-The equations for the critical ratio of a compressible gas is based on

P1 and the ratio, k of the specific heats of the gas for constant pressure, , and

constant volume .(See Table I for values of k.)

For natural gas this ratio is 0.55.

2. 0 Subsonic Orifice Flow Equation-Subsonic flow conditions exist where

.

M = 28.964 G

3. 0 Sonic Orifice Flow Equation-Sonic flow conditions exist where

14

These flow graphs are to be used as an aide in selecting the size and number of taps necessary to

flow a given amount of gas as various pressure drops across a hot tap opening. Under normal

circumstances, a pressure drop of approximately 1 psi across the top is ideal. Pipeline pressure or

size limitations may not allow a drop of 1 psi across the hot tap. The flow charts will provide the

amount of flow possible given the actual pressure drop up to and including 8 psi.

There are certain parameters which must be met in order to obtain accurate results from these

graphs. For a hot tap opening, the orifice is in a curved surface (the side of the pipeline being

tapped) and flow through the orifice enters the pipeline flow perpendicularly. The orifice

coefficient decreases the calculated flow value to adjust for this geometry. To calculate flow

through an orifice with geometry that differs from a hot tap, the orifice coefficient should be

adjusted to reflect the differing geometry. If the pipeline pressure varies substantially from 800

psig, the orifice flow equation (utilizing the actual pipeline pressure) should be used to determine

the flow volume. In special circumstances, when much larger pressure drops across the orifice

are encountered (P2< .55 P1), sonic flow formulations must be used to determine the flow

volume. For more detailed explanation of the orifice flow equation, foe both sonic and subsonic

flow, reference the Onshore Pipeline design Catalog of TI-59 software and the Design Procedure

Manual.

Where: A = Orifice area, square inches

Qm = Flow, standard cubic ft. per minute

M = Molecular weight of flowing gas

T = Inlet temperature,

K = Orifice coefficient, use

Z = Compressibility factor for inlet conditions,

(see AGA Report NO. 3 for Fpv.)


Pipeline Facilities

15

Relief Valve: Sizing for Gas or Vapor Relief

CRITICAL FLOW BEHAVIOR

If a compressible gas is expanded across a nozzle, an orifice, or the end of a pipe, its velocity and

specific volume increase with decreasing downstream pressure. For a given set of upstream

conditions (using the example of a nozzle), the mass rate of flow through the nozzle will increase

until a limiting velocity is reached in the throat .It can be shown that the limiting velocity is the

velocity of sound in the flowing media at that location. The flow rate that corresponds to the

limiting velocity is known as the critical flow rate.

The absolute pressure ratio of the pressure in the throat at sonic velocity to the inlet

pressure is called critical pressure ratio. is known as the critical flow pressure.

Under critical flow conditions, the actual pressure in the throat cannot fall below the critical flow

pressure even if a much lower pressure exists downstream. At critical flow, the expansion from

throat pressure to downstream pressure takes place irreversibly with energy dissipated in

turbulence into the surrounding fluid.

The critical flow pressure ratio in absolute units may be estimated using the ideal gas

relationship in Equation 1:

(1)

Where:

The sizing equations for pressure relief valves in vapor or gas service fall into two general

categories depending on whether the flow is critical or subcritical. If the pressure downstream of

the throat is less than or equal to the critical flow pressure, , then critical flow will occur, and

the procedures in SIZING FOR CRITICAL FLOW should be applied. If the downstream

pressure exceeds the critical pressure, , then subcritical flow will occur, and procedure in

SIZING FOR SUBCRITICAL FLOW SHOULD BE APPLIED.

SIZING FOR CRITICAL FLOW

General

Pressure relief valves in gas or vapor service that operate under critical flow conditions may be

sized using Equations 2-4. Each of the equations may be used to calculate the effective discharge

area, A, required to achieve a required flow rate through a pressure relief valve. A valve that has

an effective discharge area equal to or greater than the calculated value of A is then chosen for

the application.

16

Where:

A = required effective discharge area of the valve, in square inches.

W = required flow through the valve, in pounds per hour.

C = coefficient determined from an expression of the ratio of the specific heats of the

gas or vapor at standard conditions. This can be obtained from Figure 26 or Table 9.

Note: See for applications that involve superimposed back pressure of a magnitude that will

cause critical flow.

T = relieving temperature of the inlet gas or vapor, in degrees Rankine

(degrees Fahrenheit + 460).

Z = compressibility factor for the deviation of the actual gas from a perfect gas,

a ratio evaluated at inlet conditions.

M = molecular weight of the gas or vapor. Various handbooks carry tables

of molecular weights of materials, but the composition of the flowing

gas or vapor is seldom the same as that listed in tables. This value should be

obtained from the process data. Table 8 lists values for same common fluids.

V = required flow through the valve, in standard cubic feet per minute at 14. 7

pounds per square inch absolute and .

G = specific gravity of gas referred to air = 1.00 for air at 14.7 pounds per square

inch absolute and .

The value of the coefficient C can be evaluated from the expression of the ratio of the specific

heats of the gas or vapor.

The ratio of specific heats of any ideal gas and possibly the ratio of specific heats of a diatomic

actual gas can be found in any acceptable reference work.

When k cannot be determined, it is suggested that C = 315.

SIZING FOR SUBCRITICAL FLOW: GAS OR

VAPOR OTHER THAN STEAM

General

Pipeline Facilities

17

When the ratio of back pressure to inlet pressure exceeds the critical pressure ratio , the

flow through the pressure relief valve is subcritical . Equation 5 - 7 may be used to calculate the

required effective discharge area for a conventional relief valve that has its spring setting

adjusted to compensate for superimposed back pressure and for sizing a pilot-operated relief

valve.

Note: Balanced-bellows relief valves that operate in the subcritical region should be sized using

Equations 2-4. The back pressure correction factor for this application should be obtain from the

valve manufacturer.

Where:

A = required effective discharge area of the valve, in square inches.

W = required flow through the valve, in pounds per hour.

=

k = ratio of the specific heats.

r = ratio of back pressure to upstream relieving pressure, .

Z = compressibility factor for the deviation of the actual gas from a perfect gas,

a ratio evaluated at inlet conditions.

T = relieving temperature of the inlet gas or vapor, in degrees Rankine (degrees

Fahrenheit + 460).

M = molecular weight of the gas or vapor. Various handbooks carry tables of

molecular weights of materials, but the composition of the flowing gas or vapor is

seldom the same as that listed in tables.

V = required flow through the valve, in standard cubic feet per minute at 14.7 pounds

per square inch absolute and .

G = specific gravity of gas referred to air = 1.00 for air at 14.7 pounds per square inch

absolute and .

References:

ASME - Boiler and Pressure Vessel Code, Section VIII

18

API Recommended Practice 520, Sixth Edition


Pipeline Facilities

19

Relief Valves: Reaction Force in an Open Discharge System

Reference: API RP 520 Part 2


20

Reinforcement of Welded Branch Connection

One of the first methods of providing branch connections was to stub a branch line into a run.

Sometimes a pad would also be used to reinforce the connections. The figure below shows a

header with pad-reinforced branch connections. Although tees and extrusions have generally

taken the place of reinforced branch connections, an example calculation is presented for the

occasional instance where the designer may want to use this type of connection.

Nomenclature:

Refer to figure for a physical representation of the applicable terms.

Pipeline Facilities

21

d = Outside diameter of branch pipe.

D = Outside diameter of the run.

E = The longitudinal joint factor determined in accordance with

49 CFR 192.105.

F = The design factor determined in accordance with 49 CFR

192.105.

L = Height of the reinforcement zone

L is lesser of:

1. 2.5 , or

2. 2.5

P = The design pressure of the branch connection.

S = The yield strength of the component

being considered (i.e., run, branch or pad).

T = The temperature derating factor determined in accordance

with 49 CFR 192.105.

Reference:

ASME B31.8 Gas Transmission and Distribution Piping Systems, Appendix F


23

Pipeline Compressors

Centrifugal Compressor - Adiabatic Head

CNGA/GPSA Compressibility Factor Approximation

This approximation will produce results sufficiently accurate for preliminary calculations.

Reference:

1. Engineering Data Book, Volume 1, Gas Processors Suppliers Association, Tenth

Edition

2. Compressor Station Operation, Book T-2, GEOP, American Gas Association

(A.G.A.)

24

3. Compressor Selection and Sizing, Royce N. Brown, Second Edition, Gulf

Professional Publishing



25

Centrifugal Compressor - Required Adiabatic Horsepower


26


Brake Horsepower

Reference:


Edition


(A.G.A.)





27

Centrifugal Compressor - Required Polytropic Horsepower


28


Brake Horsepower

Reference:


Edition


(A.G.A.)





29

Centrifugal Compressor - Fan Laws

Reference:


Edition


30

Reciprocating Compressors - Capacity and Horsepower

Piston Displacement

Reciprocating Compressor Volumetric Efficiency


31

32



Reciprocating Compressor Horsepower

Reference:


Edition


(A.G.A.)





33

Discharge Temperature

Ideal Discharge Temperature

Theoretical Discharge Temperature

Actual Discharge Temperature

Reference:


Edition


(A.G.A.)




34

Compressor Station Piping - Diameter and Gas Velocity

Note: Gas velocity in piping should not exceed 2,000 [ft/min].

Reference: Compressor Station Operation, Book T-2, GEOP, American Gas Association

(A.G.A.)



35

Local Atmospheric Pressure

The local atmospheric pressure may be calculated using Smithsonian Metrological Tables:

Reference: American Gas Association, Report No.3, A.G.A. Catalog No. XQ9210


37

Accidental Gas Releases and Pipeline

Rupture

Accidental Gas Release through a Small Hole from

Pressurized Gas Pipeline

When the hole diameter in pipeline is relatively small, the pipeline is considered as a tank.

Gas release rate would be calculated by the small hole model. Assumptions made are:

pressure inside the pipeline will not be affected by gas release; gas expansion is isentropic.

Therefore, the gas release rate is constant and equal to the initial maximum release rate.

The value of the release rate at the orifice depends on whether gas flow is choked/ sonic or

subsonic. This is defined by the critical pressure ratio (CPR)

Choked flow occurs when the ratio of the source gas pressure to the ambient atmospheric

pressure is equal to or greater than:

38

For many gases, k ranges from about 1.1 to about 1.4, and so sonic or choked gas flow

usually occurs when the source gas pressure is about 25 to 28 PSIA or greater. Thus, the

large majority of accidental gas releases will usually involve sonic/choked flow

Note: No general consensus is currently available for small hole size definition. However, a

number of methodologies are suggested:

World Bank (1985) suggests characteristic hole sizes for a range of process

equipment (e.g., for pipes 20% and 100% of pipe diameter are proposed).

Some analysts use 2 and 4-inch holes, regardless of pipe size.

Some analysts use a range of hole sizes from small to large, such as 0.2,1,4 and 6 inches and

full bore ruptures for pipes less than 6-inches in diameter.

Some analysts use more detailed procedures. They suggest that 90% of all pipe failures

result in a hole size less than 50% of the pipe area. The following approach may be

consider :

-For small bore piping use 5-mm and full-bore ruptures.

-For 2-6" piping use 5-mm, 25-mm and full-bore holes.

-For 8-12" piping use 5-, 25-, 100-mm and full-bore holes.

To convert lb/hr to SCFM

To convert lb/hr to SCFH

Accidental Gas Releases and Pipeline Rupture

39

References:

- Handbook of Chemical Hazard Analysis Procedures,

- Risk Management Program Guidance for Offsite Consequence

- API Recommended Practice 520, Sizing, Selection, and Installation of Pressure-Relieving

Devices in Refineries, Part I, American Petroleum Institute,

- API Recommended Practice 521, Guide for Pressure-Relieving and Depressuring

Systems, American Petroleum Institute,

- Crane Limited, Flow of Fluids through Valves, Fittings, and Pipe, Technical Paper No.

410-C, Crane Engineering Division

- Bosch, C.J.H. van den and N.J. Duijm, The Netherlands Organization of Applied

Scientific Research. Methods for the Calculation of Physical Effects, CPR 14E: Part (TNO

Yellow Book),

- Ramskill, P.K., Discharge Rate Calculation Methods or Use in Plant Safety Assessments,

Safety and Reliability


40

Accidental Gas Release Rate from a Full-Bore Pipeline

Rupture

Reference:

- GRI-00/0189, A Model for Sizing High Consequence Areas Associated with Natural Gas

Pipelines, Gas Technology Institute

- PHMSA - Final Report TTO Number 13, Delivery Order DTRS56-02-D-70036, Michael

Baker Jr., Inc.

- PHMSA - Final Report TTO Number 14, Delivery Order DTRS56-02-D-70036, , Michael

Baker Jr., Inc.

- Crane Limited, Flow of Fluids through Valves, Fittings, and Pipe, Technical Paper No.

410-C, Crane Engineering Division



41

Pack in Pipeline

Pack in pipeline - Isolated pipe section Gas packed in isolated section of the pipeline can be calculated in the same way where,

P1 = P2 = Ps

42

Compressibility factor Z is calculated using procedure from Engineering Data Book, Volume II,

Gas Processor Association, Revised Tenth Edition, 1994

References:

1. Pipeline Design for Hydrocarbons Gases and Liquids, Committee of pipeline planning,

American Association of Civil Engineers, 1975

2. Engineering Data Book, Volume II, Gas Processor Association, Revised Tenth Edition,

1994

3. Pipeline Design & Construction, A Practical Approach, American Society of Mechanical

Engineers, 2000



43

Natural Gas Pipeline Rupture - Depth, Radius, & Width of

Crater

A. GASUNIE MODEL

This model applies to a guillotine rupture wherein two separate pipe ends exists after the

rupture.

Figure 1

44

The crater angles are determined from empirical equations:

Considering crater and dimensions shown in Figure 1. The equation of the ellipse is given

by

Differentiating this at the ground level and substituting for x gives

Evaluating this on the ground level and half crater depth gives

These can be solved simultaneously

The width of crater W is given by

B. NEN 3651 MODEL RADIUS OF THE CRATER

Model may be applied for guillotine type rupture, NEN 3651 define radius of the crater as:

Note: Units for pipe internal pressure p0 are in bars.

C. PRCI/GASUNIE/BATTELLE COMBINED MODEL

This model may be applied for guillotine type rupture only. Computation of the crater

depth in combined PRCI/Gasunie/Battelle model is the same as described above for

Gasunie model.

The crater width is calculated as:


45

Reference:

1. Schram, W., “Prediction of Crater Caused by Underground Pipeline Rupture”,

N.V. Nederalandse Gasunie, Report TR/T 97.R.2515

2. NEN 3651, Annex A: “Determining Disturbance Zone Dimension”

3. PRCI L51861, “Line Rupture and Spacing of Parallel Lines”, Battelle Memorial

Institute


47

Gas Pipeline Hydraulics

Gas Pipeline Hydraulics - A.G.A - Fully Turbulent Flow Equation

For the fully turbulent zone the transmission factor is determined from the Von Karman rough

pipe flow law.

Nomenclature


48

Gas Pipeline Hydraulics - Colebrook - White Equation

The Colebrook-White equation is recommended for use by those unfamiliar with pipeline flow

equations, since it will produce the greatest consistency of accuracy

over the widest possible range of variables.

Nomenclature



49

Gas Pipeline Hydraulics - IGT Distribution Equation

Nomenclature


50

Gas Pipeline Hydraulics - Mueller - High Pressure

The Mueller High Pressure equation is used in distribution systems with pressures greater than 1

psig.

Nomenclature



51

Gas Pipeline Hydraulics - Mueller - Low Pressure

The Mueller Low Pressure equation is used in distribution systems with pressures less than 1

psig.

Nomenclature


52

Gas Pipeline Hydraulics - Panhandle - A Equation

The Panhandle A equation was originally developed from Reynolds numbers in the range of:

The average pipeline efficiency factor of 0.92 normally used in this Panhandle A equation was

obtained from actual empirical experience with the metered gas flow rates corrected to standard

conditions. The Panhandle A equation provides a reasonable approximation for partially

turbulent flow; however, for fully turbulent flow, the Panhandle A equation is not realistic. In the

fully turbulent region, the Panhandle B equation is recommended.

Pipeline efficiency factors used in the Panhandle equations should be reduced for smaller pipe

diameters. For large diameter lines, the efficiency factor may be as high as 0.98.

Nomenclature



53

Gas Pipeline Hydraulics - Panhandle - B Equation

The Panhandle B equation is used in the design of large high pressure, long transmission

pipelines. The Panhandle B equation is considered suitable for Reynolds numbers from:

Pipeline efficiency factors used in the Panhandle equations should be reduced for smaller pipe

diameters. For large diameter lines, the efficiency factor may be as high as 0.98.

Nomenclature


54

Gas Pipeline Hydraulics - Pittsburgh Equation

The Pittsburgh equation is used in low pressure pipelines within the following range:

Nomenclature



55

Gas Pipeline Hydraulics - Spitzglass Equation

The Spitzglass equation is used with pipe diameters of 10" or less and with a range of pressure:

Nomenclature


56

Gas Pipeline Hydraulics - Weymouth Equation

The Weymouth equation is one of the older equations, but is still widely used for distribution and

gathering systems. It was originally developed from data taken on small, low to medium pressure

pipelines. When it is used for larger, high pressure pipelines it is quite conservative, as it predicts

values for Q which could be 8-12% low

For gas transmission through long pipelines, the Weymouth equation is not recommended.

The Weymouth equation is typically used for flow conditions :

Nomenclature


57

Steel Pipe - Design & Stress Analysis

Design Pressure - Steel Pipe

Note : For design limitations and definitions, see CFR Code Part 192 in the Standars and regulations

Regulations Module.


58



Regulations Module.



59

Restrained Gas Pipeline - Stress Analysis

Hoop Stress

Longitudinal Stress due to Internal Pressure

Longitudinal Stress due to Thermal Expansion

Nominal Bending Stress

Stress due to Axial Loading

Net Longitudinal Stresses

60

Combined Biaxial Stress

Reference: ASME B31.8 - 2010



61

Unrestrained Gas Pipeline Stress Analysis - Steel Pipe

Hoop Stress

Longitudinal Stress due to Internal Pressure

Nominal Bending Stress

Stress due to Axial Loading

Net Longitudinal Stresses

Reference: ASME B31.8 - 2010


62



Regulations Module.



63



Regulations Module.


64

Design Pressure - Plastic Pipe

Design pressure for plastic pipe is determined in accordance with either of the following

formulas :

Note :

For design limitations and definitions, see DOT Code 192 in the DOT & MMS Regulations

Module !



65

Design Pressure - Plastic Pipe

Design pressure for plastic pipe is determined in accordance with either of the following

formulas :

Note :

For design limitations and definitions, see DOT Code 192 in the DOT & MMS Regulations

Module !


66

Hoop and Longitudinal Stress

Hoop stress is determined by Barlow's formula

Longitudinal stress



67

Flume Design

ESTIMATING ROUGHNESS COEFFICIENTS

This section describes a method for estimating the roughness coefficient n for use in

hydraulic computations associated with natural streams, floodways, and excavated

channels. The procedures applies to the estimation of n in Manning's formula .

The coefficient of roughness n quantifies retardation of flow due to roughness of channel

sides, bottom, and irregularities.

Estimation of n requires the application subjective judgement to evaluate five primary

factors:

- Irregularity of the surfaces of the channel sides and bottom;

- Variations in the shape and size of the channel cross sections;

- Obstructions in the channel;

- Vegetation in the channel;

- Meandering of the channel.

Procedure for estimating n

The procedure for estimating n involves selecting a basic value for a straight, uniform,

smooth channel in the existing soil materials, then modifying that value with each of the

five primary factors listed above.

In selecting the modifying values, it is important that each factor be examined and

considered independently.

Step 1. Selection of basic value of n. Select a basic n value for straight, uniform, smooth

channel in the natural materials involved. The conditions of straight alignment, uniform

cross section, and smooth side and bottom surfaces without vegetation should be kept in

mind. Thus, basic n varies only with the material that forms the sides and bottom of the

channel. Select the basic n for natural or excavated channels from Table 8.04a. If the

bottom and sides of a channel consist of different materials, select an intermediate value.

Table 8.04a. Basic Value of Roughness Coefficient for Channel Materials

Soil Material Basic n

Channels in earth 0.02

Channels in fine gravel 0.024

Channels cut into rock 0.025

Channels in coarse gravel 0.028

Step 2.Selection of modifying value for surface irregularity. This factor is based on the

degree of roughness or irregularity of the surfaces of the channel sides and bottom.

Consider the actual surface irregularity, first in relations to the degree of surface

smoothness obtainable with the natural materials involved, and second in relation to the

depth of flow expected. If the surface irregularity is comparable to the best surface possible

for the channel materials, assign a modifying value zero. Irregularity induces turbulence

that calls for increased modifying values. Table 8.04b may be used as a guide to selection of

these modifying values.

Table8.04b. Modifying Value for Roughness Coefficient Due to Surface Irregularity of

Channels

Degree of Surface Comparable Modifying

68

Irregularity Value

Smooth The best obtainable for the material 0.000

Minor Well-dredged channels; slightly eroded

or scoured side slope of canals or

drainage channels 0.005

Moderate Fair to poorly dredged channels;

moderately sloughed or eroded side

slopes of canals or drainage channels 0.010

Severe Badly sloughed banks of natural channels:

badly eroded or sloughed sides of canals

or drainage channels; unshaped, jagged

and irregular surfaces of channels excavated

in rock 0.020

Source for Tables b-f: Estimating Hydraulic Roughness Coefficients

Step 3. Selection of modifying value for variations in the shape and size of cross sections. In

considering this factor, judge the approximate magnitude of increase and decrease in

successive cross sections as compared to the average. Gradual and uniform changes do not

cause significant turbulence. Turbulence increases with the frequency and abruptness of

alternation from large to small channel sections.

Shape changes causing the greatest turbulence are those for which flow shifts from side to

side in the channel. Select modifying values based on Table 8.04c.

Table 8.04c. Modifying Value for Roughness Coefficient Due to Variations of Channel

Cross Section

Character of Variation Modifying

Value

Changes in size or shape occurring

gradually 0.000

Large and small sections alternating

occasionally, or shape changes causing

occasional shift of main flow from side

to side 0.005

Large and small sections alternating

frequently, or shape changes causing

frequent shift of main flow from side

to side 0.010-0.015

Step 4. Selection of modifying value for obstructions. This factor is based on the presence

and characteristics of obstructions such as debris deposits, stumps, exposed roots, boulders,

and fallen and lodged logs. Take care that conditions considered in other steps not be

double-counted in this step.

In judging the relative effect of obstructions, consider the degree to which the obstructions

reduce the average cross-sectional area at various depths and the characteristic of the

obstructions. Shaped-edged or angular objects induce more turbulence than curved,

smooth-surfaced objects. Also consider the transverse and longitudinal position and

spacing of obstruction in the reach. Select modifying value based on Table 8.04d.

Table 8.04d. Modifying Value for Roughness Coefficient Due to Obstruction in the

Channel


69

Relative Effect Modifying

of Obstruction Value

Negligible 0.000

Minor 0.010 to 0.015

Appreciable 0.020 to 0.030

Severe 0.040 to 0.060

Step 5. Selection of modifying value for vegetation. The retarding effect of vegetation is due

primarily to turbulence induced as the water flows around and between limbs, stems and

foliage and secondarily to reduction in cross section. As depth and velocity increase, the

force of flowing water tends to bend the vegetation. Therefore, the ability of vegetation to

cause turbulence is related to its resistance to bending. Note that the amount and

characteristics of foliage vary seasonally. In judging the retarding effect of vegetation,

consider the following: height of vegetation in relation to depth of flow, its resistance to

bending, the degree to which the cross section is occupied or blocked, and the transverse

and longitudinal distribution of densities and height of vegetation in the reach. Use Table

8.04e as a guide.

Table 8.04e. Modifying Value for Roughness Coefficient Due to Vegetation in the Channel

Vegetation and Flow Conditions Range in Modifying Value

Comparable to:

Low Effect 0.005 to 0.010

Dense growths of flexible turf grass or

weeds, such as Bermudagrass and Kentacky

bluegrass. Average depth of flow 2 to 3 times

the height of the vegetation.

Medium Effect 0.010 to 0.025

Turf grasses where the average depth of flow

is 1 to 2 times the heigth of vegetation

Stemmy grasses, weeds or tree seedlings

with moderate cover where the average

depth of flow is 2 to 3 times the height

of vegetation

Brushy growths, moderately dense, similar

to willow 1 to 2 years old, dormant season,

along side slopes of channel with no significant

egetation along the channel bottom, where the

hydraulic radius is greater then 2 ft

High Effect 0.025 to 0.050

Grasses where the average depth of flow is

about equal to the height of vegetation

Dormant seasons, willow or cottonwood

tree 8-10 year old, intergrown with some

weed and brush; hydraulic radius 2 to 4 ft

1. yr old, intergrown with some weeds in

70

full foliage along side slopes; no significant

egetation along channel bottom; hydraulic

radius 2 to 4 ft

Grasses where average depth of flow is less

than one-half the height of vegetation

Very High Effect 0.050 to 0.100

Growing season, bushy willows about 1-yr

old, intergrown with weeds in full foliage

along side slopes; dense grown of cattails

or similar rooted vegetation along channel

bottom; hydraulic radius greater than 4 ft

Growing season, tree intergrown with weeds

and brush, all in full foliage; hydraulic radius

greater than 4ft

Step 6 Computation of n for the reach. The first estimate of roughness for the reach

n , is obtained by neglecting meandering and adding the basic n value obtained in step 1

and modifying value from steps 2 through 5.

Step 7. Meander. The modifying value for meandering is not independent of the other

modifying values. It is estimated from the n obtained in step 6, and the ratio of the

meandering length to the straight length. The modifying value for meandering may be

selected from Table 8.04f.

Table 8.04f.Modifying Value for Roughness Coefficient Due to Meander of the Channel

Meander Ratio Degree of Modifying

Meandering Value

0.0 to 1.2 Minor 0.000

1. 2 to 1.5 Appropriable 0.15 n

1. 5 and greater Severe 0.30 n

Step 8. Computation of n for a channel reach with meandering. Add the modifying value

obtained in step 7, to n , obtained in step 6.

The procedure for estimating roughness for an existing channel is illustrated in Sample

Problem 8.04a.

Sample Problem 8.04a. Estimation of roughness coefficient for an existing channel.

Description of reach:


71

Soil - Natural channel with lower part of banks and bottom yellowish gray

clay, upper part light silty clay.

Side slopes - Fairly regular; bottom uneven and irregular.

Cross section - Very little variation in the shape; moderate, gradual

ariation in size. Average cross section approximately trapezoidal with

side slopes about 1,5:1 and bottom width about 10 ft. At bankfull stage,

the average depth is about 8.5 ft and the average top width is about 35 ft.

Vegetation - Side slopes covered with heavy growth of poplar tree,

2. to 3 inches in diameter, large willows, and climbing vines; thick,

bottom growth of waterweed; summer condition with the vegetation

in full foliage.

Alignment - Significant meandering; total length of meandering

channel, 1120 ft; straight line distance, 800 ft.

Solution:

Step Description

Number n Value

1. Soil materials indicate minimum basic n 0.02

Modification for:

2. Moderately irregular surface 0.01

3. Change in size and shape judged insignificant 0.00

4. No obstructions indicted 0.00

5. Dense vegetation 0.08

6. Straight channel subtotal, n = 0.11

7. Meandering appreciable,

meandering ratio: 1120/800 = 1.4

Select 0.15 from Table 8.04f

8. Modified value =(0.15)(0.11) = 0.0165 or 0.02

Total roughness coefficient n = 0.13

Out-of-Bank Condition Channel and Flood Plain Flow

Work with natural floodways and streams often requires consideration of a wide range of

discharges. At high stages, both channel and overbank or flood plain flow may occur.

Usually, the retardance of the flood plain differs significantly from that of the channel, and

the hydraulic computations can be improved by subdividing the cross selection and

assigning different n values for flow in the channel and the flood plain. If conditions

72

warrant, the flood plain may be subdivided further. Do not average channel n with flood

plane n. The n value for in-bank flow in the channel may be averaged.

To compute a roughness coefficient for flood plain flow, consider all factors except

meandering. Flood plain n values normally are greater than channel values, primarily due

to shallower depths of flow. The two factors requiring most careful consideration in the

flood plain are obstructions and vegetation. Many flood plains have fairly dense networks

of obstructions to be evaluated. Vegetation should be judged on the basis of growing-season

conditions.

The overland flow portion of flow time may be determined from Figure 8.03a.The flow

time (in minutes) in the channel can be estimated by calculating the average velocity in feet

per minute and dividing the length (in feet) by the average velocity.

Table 8.03a Value of Runoff Coefficient (C) for Rational Formula

Land Use C Land Use C

Business: Lawns:

Downtown areas 0.70-0.95 Sandy soil, flat, 2% 0.05-0.10

Neighborhood areas 0.50-0.70 Sandy soil, ave., 2-7% 0.10-0.15

Sandy soil, steep, 7% 0.15-0.20

Residential: Heavy soil, flat, 2% 0.13-0.17

Single-family areas 0.30-0.50 Heavy soil, ave., 2-7% 0.18-0.22

Multi units, detached 0.40-0.60 Heavy soil, steep, 7% 0.25-0.35

Multi units, attached 0.60-0.75

Suburban 0.25-0.40 Agricultural land:

Bare packed soil

Industrial: Smooth 0.30-0.60

Light areas 0.50-0.80 Rough 0.20-0.50

Heavy areas 0.60-0.90 Cultivated rows

Heavy soil no crop 0.30-0.60

Parks, cemeteries 0.10-0.25 Heavy soil with crop 0.20-0.50

Sandy soil no crop 0.20-0.40

Play grounds 0.20-0.35 Sandy soil with crop 0.10-0.25

Pasture

Railroad yards areas 0.20-0.40 Heavy soil 0.15-0.45

Sandy soil 0.05-0.25

Unimproved areas 0.10-0.30 Woodlands 0.05-0.25

Streets:

Asphalt 0.70-0.95

Concrete 0.80-0.95

Brick 0.70-0.85

Drives and walks 0.75-0.85

Roofs 0.75-0.85

NOTE: The designer must use judgment to select the appropriate C value within the range

for the appropriate land use. Generally, large areas with permeable soils, flat slopes, and

dense vegetation should have lowest C values. Smaller areas with slowly permeable soils,

steep slopes, and sparse vegetation should be assigned highest V value.

Sources: American Society of Civil Engineers


73

Step 4. Determine the rainfall intensity, frequency, and duration (Figure 8.03b through

8.03g - source: North Carolina State Highway Commission; Jan.1973). Select the chart for

the locality closest to your location. Enter the "duration" axis of the chart with the

calculated time of concentration,. . More vertically until you intersect the curve of the

appropriate design storm, then move horizontally to read the rainfall intensity factor, i, in

inches per hour.

Step 5. Determine peak discharge, Q , by multiplying the previously determined

factors using the rational formula (Sample Problem 8.03a)

Sample Problem 8.03a Determination of peak runoff rate using the rational method.

Q = CiA

Given:

Drainage area: 20 acres

Graded areas: 12 acres

Woodland: 8 acres

Maximum slope length: 400 ft

Average slope: 3% area bare

Location: Raleigh, NC

Find:

Peak runoff rate from 10-yr frequency storm

Solution:

(1) Drainage area: 20 acres (given)

(1) Determine runoff coefficient, C.

Calculate Weighted Average

Area C from Table 8.03a

Graded 12 x 0.45 = 5.4

Woodland 8 x 0.15 = 1.2

20 6.6

C = 6.6/20 = 0.33

1. Find the time of concentration, from Figure 8.03a using maximum

length of travel = 400ft and height of most remote point above outlet

= 400 ft x 3% = 12 ft; assuming overland flow on bare earth.

= 3.2 minutes.

NOTE: Any time of flow in channel should be added to the overland flow to

determine .

(1) Determine the rainfall intensity factor, i.

i = 8.0 inches/hr (from Figure 8.03e) using 10-yr storm,

5 min. duration.

(1) Q = C(i)(A)

Q = 0.33 (8.0)(20) = 52.8 cfs; Use 53 cfs

74

Table 8.05a

Maximum Allowable Design Velocity

For Vegetated Channels

Typical Soil Grass Lining Permissible Velocity

Channel Slope Characteristic for Established Grass

Application Lining (ft/sec)

0-5% Easily Erodible Bermudagrass 5.0

Non_plastic Tail fescue 4.5

(Sand & Silts) Bahiagrass 4.5

Kentucky bluegrass 4.5

Grass-legume mixture 3.5

Erosion Resistant Bermudagrass 6.0

Plastic Tall fescue 5.5

(Clay mixes) Bahiagrass 5.5



5-10% Easily Erodible Bermudagrass 4.5







(Clay Mixes) Bahiagrass 5.0



>10% Easily Erodible Bermudagrass 3.5






(Clay Mixes) Bahiagrass 3.5


Source: USDA-SCS Modified

NOTE:

Selecting Channel Cross-Section Geometry

To calculate the required size of an open channel, assume the design flow is uniform and

does not vary with time. Since actual flow conditions change throughout the length of a

channel, subdivide the channel into design reaches and design each reach to carry the

appropriate capacity.


75

The three most commonly used channel cross-section are "V"-shaped, parabolic, and

trapezoidal. Figure 8.05b gives mathematical formulas for the area, hydraulic radius and

top width of each of these shapes.

Table 8.05b Manning's n for Structure Channel Linings

Channel Lining Recommended

n values

Asphaltic concrete, machine placed 0.012

Asphalt, exposed prefabricated 0.015

Concrete 0.015

Metal, corrugated 0.024

Plastic 0.013

Shotcrete 0.017

Gabion 0.030

Earth 0.020

Erosion Control Blankets 0.030

Source: American Society of Civil Engineers (modified)

Design Procedure-Permissible Velocity

The following is a step-by-step procedure for designing a runoff conveyance channel using

Manning's equation and the continuity equation:

Step1. Determine the required flow capacity, Q, by estimating peak runoff rate for the

design storm (Appendix 8.03).

Step2. Determine the slope and select channel geometry and lining.

Step3. Determine the permissible velocity for the lining selected, or the desired velocity, if

paved. (see Table 8.05a,pg. 8.05.4)

Step 4. Make an initial estimate of channel size - divide the required Q by the permissible

velocity to reach a "first try" estimate of channel flow area. Then select a geometry, depth

and top width to fit site conditions.

Step 5. Calculate the hydraulic radius, R, from channel geometry (Figure 8.05b,pg.8.05.5).

Step 6. Determine roughness coefficient n.

Structural Lining - see Table 8.05, pg. 8.05.6

Grass Lining:

. Determine retardance class for vegetation from Table 8.05c, pg.8.05.8

To meet stability requirement, use retardance for newly mowed condition

( generally C and D). To determine channel capacity, use at least one retardance class

higher.

. Determine n from Figure 8.05c, pg.8.05.7

.

Step 7. Calculate the actual channel velocity and required, V, using Manning's equation

(Figure 8.05a, pg. 8.05.3), and calculate channel capacity, Q, using the continuity equation.

Step 8. Check results against permissible velocity and required design capacity to

determine if design is acceptable.

Step 9. If design is not acceptable, alter channel dimension as appropriate. For trapezoidal

channels, this adjustment is usually made by changing the bottom width.

Sample Problem 8.05a Design of a grass-lined channel

Channel summary

Trapezoidal shape, Z = 3, B = 3 ft, d = 1,5 ft, grade = 2%

76

Note: In Sample Problem 8.05a the "n-value" is first choosen based on a permissible

velocity and not a design velocity criteria. Therefore the use of table 8.05c may not be

accurate as individual retardance class charts when a design velocity is the determining

factor.

Tractive Force Procedure

The design of riprap-lined channel and temporary channel linings is based on analysis of

tractive force.

NOTE: The procedure is for uniform flow in channels and is not to be used for design of

deenergizing devices and may not be valid for larger channels.

To calculated the required size of an open channel, assume the design flow is uniform and

does not vary with time. Since actual flow conditions change through the length of a

channel, subdivide the channel into design reaches as appropriate.

PERMISSIBLE SHEAR STRESS

The permissible shear stress, , is the force required to initiate movement of the lining

material. Permissible shear stress for the liner is not related to the erodibility of the

underlying soil. However, if the lining is eroded or broken, the bed material will be exposed

to the erosive force of the flow.

COMPUTING NORMAL DEPTH

The first step in selecting an appropriate lining is to compute the design flow depth (the

normal depth) and determine the shear stress.

Normal depth can be calculated by Manning's equation as shown for trapezoidal channel

in Figure 8.05d. Values of the Manning's roughness coefficient for different ranges of depth

are provided in Table 8.05e for temporary lining and Table 8.05f for riprap. The coefficient

of roughness generally decrease with increase flow depth.

Table 8.05e Manning's Roughness Coefficient for Temporary Lining Materials

n value for Depth Ranges

0-0.5 ft 0.5-2.0 ft >2.0 ft

Lining Type

Woven Paper Net 0.016 0.015 0.015

Jute Net 0.028 0.022 0.019

Fiberglass Roving 0.028 0.021 0.019

Straw with Net 0.065 0.033 0.025

Curled Wood Mat 0.066 0.035 0.028

Synthetic Mat 0.036 0.025 0.021

Adapted from: FHWA-HEC 15, pg.37-April 1988

Table 8.05f Manning's Roughness Coefficient

n-value

n value for Depth Ranges

Lining Category Lining Type 0-0.5 ft 0.5-2.0 ft 2.0 ft

(0-15 cm) (15-60cm) (>60cm)

Rigid Concrete 0.015 0.013 0.013

Grouted Riprap 0.040 0.030 0.028

Stone Masonry 0.042 0.032 0.030

Soil Cement 0.025 0.022 0.020


77

Asphalt 0.018 0.016 0.016

Unlined Bare Soil 0.023 0.020 0.020

Rock Cut 0.045 0.035 0.025

Gravel Riprap 1-inch (2.5 cm) 0.044 0.033 0.030

2-inch (5-cm) 0.066 0.041 0.034

Rock Riprap 6-inch (15-cm) 0.104 0.069 0.035

12-inch (30-cm) -- 0.078 0.040

Note:Values listed are representative values for the respective depth ranges. Manner's

roughness coefficient, n, vary with the flow depth.

DETERMINING SHEAR STESS

Shear stress, T, at normal depth is computed for lining by the following equation:

T = yds

= Permissible shear stress

where:

T = shear stress in

y = unit weight of water, 62.4

d = flow depth in ft

s = channel gradient in ft/ft.

If the permissible shear stress, , given in Table 8.05g is greater than the computed shear

stress, the riprap or temporary lining is considered acceptable. If a lining is unacceptable,

select a lining with a higher permissible shear stress and repeat the calculations for normal

depth and shear stress. In some cases it may be necessary to alter channel dimensions to

reduce the shear stress.

Computing tractive force around a channel bend requires special considerations because

the change in flow direction imposes higher shear stress on the channel bottom and banks.

The maximum shear stress in a bend, , is given by the following equation:

where:

The value of is related to the radius of curvature of the channel at its center line, ,

and the bottom width of the channel, B, Figure 8.05e. The length of channel requiring

protection downstream from a bend, , is a function of the roughness of the lining

material and the hydraulic radius as shown in Figure 8.05f.

Table 8.05g Permissible Shear Stresses for Riprap and Temporary Liners

Permissible Unit Shear Stress, T

Lining Category Lining Type

Temporary Woven Paper Net 0.15

78

Jute Net 0.45

Fiberglass Roving:

Single 0.60

Double 0.85

Straw with Net 1.45

Curled Wood Mat 1.55

Synthetic Mat 2.00

Erosion Control Blankets 2.25

Gravel Riprap 1 0.33

2. 0.67

Rock Riprap 6 2.00

9 3.00

12 4.00

15 5.00

15 6.00

21 7.80

24 8.00

Adapted From FHWA, HEC-15, April 1983, pgs. 17 & 37.

Design Procedure-Temporary Liners

The following is a step-by-step procedure for designing a temporary liner for a channel.

Because temporary liners have a short period of service, the design Q may be reduced. For

liners that are needed for six months or less, the 2-yr frequency storm is recommended.

Step 1. Select a liner material suitable for site conditions and application. Determine

roughness coefficient from manufacturer's specifications or Table 8.05e, pg.8.05.10.

Step 2. Calculate the normal flow depth using Manning's equation.Check to see that depth

is consistent with that assumed for selection of Manning's in Figure 8.05d, pg.8.05.11.For

smaller runoffs Figure 8.05d is not as clearly defined. Recommended solutions can be

determined by using the Manning equation.

Step 3. Calculate shear stress at normal depth.

Step 4. Compare computed shear stress with the permissible shear stress for the liner.

Step 5. If computed shear is greater than permissible shear, adjust channel dimension to

reduce shear or select a more resistant lining and repeat step 1 through 4.



79

Natural Gas Pipeline Rupture - Depth, Radius, & Width of

Crater

A. GASUNIE MODEL

This model applies to a guillotine rupture wherein two separate pipe ends exists after the

rupture.

Figure 1

80

The crater angles are determined from empirical equations:

Considering crater and dimensions shown in Figure 1. The equation of the ellipse is given

by

Differentiating this at the ground level and substituting for x gives

Evaluating this on the ground level and half crater depth gives

These can be solved simultaneously

The width of crater W is given by

B. NEN 3651 MODEL RADIUS OF THE CRATER

Model may be applied for guillotine type rupture, NEN 3651 define radius of the crater as:

Note: Units for pipe internal pressure p0 are in bars.

C. PRCI/GASUNIE/BATTELLE COMBINED MODEL

This model may be applied for guillotine type rupture only. Computation of the crater

depth in combined PRCI/Gasunie/Battelle model is the same as described above for

Gasunie model.

The crater width is calculated as:


81

Reference:

1. Schram, W., “Prediction of Crater Caused by Underground Pipeline Rupture”,

N.V. Nederalandse Gasunie, Report TR/T 97.R.2515

2. NEN 3651, Annex A: “Determining Disturbance Zone Dimension”

3. PRCI L51861, “Line Rupture and Spacing of Parallel Lines”, Battelle Memorial

Institute


82

Maximum Impact Load and Penetration Depth

A. Maximum Impact Load

B. Penetration Depth


83

Reference: “Guidelines for the Design of Buried Steel Pipe” American Lifeline Alliance


84

Pipeline Anchor Force Analysis

Tensile stress due to Poisson effect:

Compressive stress due to temperature change:

Net longitudinal stress at the beginning point ( A ) of the transition:

Net longitudinal stress at the end point ( B ) of transition:

Net strain at point B, will be:

Soil resistance force based on Wilburs formula for average soil:

Length of transition zone:


85

Total pipe movement at point B will be:

Anchor force:

Reference:

"Pipe Line Industry", Wilbur, W.E., February 1963

"Theory of Elasticity", Timoshenko, S.


86

API - 1117 Movement of In-Service Pipelines

TOTAL LONGITUDINAL STRESS

The total longitudinal stress in the pipe can be estimated

With the following equation:

Where:

LONGITUDINAL TENSILE STRESS DUE TO INTERNAL PRESSURE

The longitudinal tensile stress in the pipe due to internal pressure may be estimated with

the following equation:

Where:

LONGITUDINAL TENSILE STRESS DUE TO TEMPERATURE CHANGE

The longitudinal tensile stress in the pipe due to a change

in the temperature may be estimated with following

equation:

Where:

If the pipe's temperature at installation time is not known,


87

it should be reasonably estimated.

LONGITUDINAL FLEXURE STRESS DUE TO EXISTING ELASTIC CURVATURE

When a pipeline is laid to conform elastically to a given trench profile, the pipeline will

experience induced flexural stress in amount proportional to its curvature. In hilly terain,

where slopes are unstable, or where soils are subject to frost heave or liquefaction, the

pipeline is likely to experience stress of unpredictable and varying magnitude. This stress

(S )can range from near-yield-strength levels in tension to near-bulking levels in

compression. This existing stress should be considered prior to a movement operation.

EXISTING LONGITUDINAL STRESS

The existing longitudinal stress in a pipeline will normally be in the range of-10,000 psi to

20,000 psi. In the flat or gently rolling terrain where soils are not subject to frost heave or

liquefaction, the pipeline will experience only the longitudinal tensile stress due to internal

pressure and temperature as discussed above.

The existing longitudinal stress in the pipe may be estimated

With following equation:

Where:

S = longitudinal stress in the pipe due to existing elastic curvature, in psi.

LONGITUDINAL STRESS DUE TO BENDING

The longitudinal stress in the pipe due to bending may be

estimated with following equation:

Where:

w = net uniformly distributed load required to achieve the desired mid-span vertical

deflection of the pipe [not full weight of the pipe and fluid], in pounds per inch.

L = minimum trench length required to reach the mid-span vertical deflection of the

pipe , in inches.

S = elastic section modulus of the pipe, in inches .

LONGITUDINAL STRESS DUE TO ELONGATION

The longitudinal stress in the pipe due to elongation caused by the movement operation

may be estimated with the following equation:

Where:

= mid-span deflection of the pipe, in feet.

88

L = minimum trench length required to reach the mid-span deflection of the pipe , in

feet.

The effects of this stress may be offset by an elastic compressive stress existing in the

pipeline prior to the moving because of slack.

AVAILABLE LONGITUDINAL BENDING STRESS

The longitudinal stress available for bending may be estimated with the following equation:

Where:

S = longitudinal stress available for bending, psi.

F = design factor.

SMYS = specified minimum yield strength of the pipe, in psi.

TRENCH LENGTH

The minimum trench length required to achieve a particular mid-span deflection of the

pipe without exceeding the longitudinal stress limit can be determined with the following

equation, based on elastic free deflection theory, which treats the pipe as a single-span

beam that is fixed at both ends andthat has a uniformly distributed load:

L=

TRENCH (OR DISPLACEMENT) PROFILE

A profile for the moved portion of the pipeline should be designed to minimize induced

bending stress concentrations. Therefore, to obtain acceptable longitudinal stress

distribution due to bending, the deflection at any point along the trench profile can be

determined with the following equation:

Where:

= vertical deflection of the pipe at distance x, in feet.

x = distance along the length of the trench from the

starting point of the pipe deflection, in feet.

SUPPORTING SPACING

Based on a four-span, uniformly loaded beam, the maximum free span between supports

can be determined with the following equation:

L =

Where:

L = maximum free span between pipe supports, in feet.

d = inside diameter of the pipe, in inches.

Reference: API RP 1117 "Movement of In-Service Pipeline", Second Edition, August 1996


89


90

Pipe Requirements for Horizontally Drilled Installation

1. Determine Hoop Stress:

1. Determine Overburden Stress:

1. Determine Total Circumferential Stress:

1. Determine Bending Stress:

1. Determine Total Combined Stress and select max value:


91

1. Determine calculated design factor:

1. Determine maximum pull force:

1. Determine minimum bend radius - entry & exit at installation:

1. Maximum SMYS for hydrostatic pressure:

1. Determine maximum cantilever length

1. Determine maximum allowable hydrostatic test pressure:


92

Buoyancy Analysis and Concrete Coating Thickness

1. Determine bare pipe weight:

2. Determine total volume of pipe in air including corrosion and concrete coating:

3. Determine Volume of corrosion coating:

4. Determine volume of concrete coating:

5. Determine total weight of pipe in air, including weight of corrosion and concrete

coating:

6. Determine weight of displaced water

7. Determine the difference :


93

8. Determine bulk specific gravity:


94

Buoyancy Analysis and Concrete Weights Spacing

Buoyant Force

Weight of Steel Pipe in the Air

Weight of Pipe Coating in the Air

Weight of Product in the Pipe

Downward Force of the Pipe

Net Controlling Force


95

Downward Force of the Concrete Weight

Concrete Weight Spacing

Unit Weights:

Fresh water 62.42

Salt water 64.0

Concrete 140

Steel 490

PE Coating 59.30

FBE Coating 89.89

Wood lagging 26.84

Reference: “Pipeline Geo-Environmental Design and Geohazard Management”, ASME,

2008, Edited by Moness Rizkalla


96

Bending Stress and Deflection in Pipelines

FIXED ENDS SUPPORTS

y = maximum deflection, feet

S = maximum bending stress, PSI

W= unit weight, pounds per foot

L = length, feet

E = modulus of elasticity, PSI

steel = 30,000,000

plastic(dupont) = 100,000

plastic(plexco) = 125,000

cast iron = 15,000,000

copper = 15,000,000

D = outside diameter, inches

d = inside diameter, inches

SIMPLE SUPPORTS y = 5 times y for fixed ends

S = 1.5 times S for fixed ends

CANTILEVER SUPPORT y = 48 times y for fixed ends

S = 6 times S for fixed ends

S and y on the schematics indicate the points of

MAXIMUM stress and deflection.



97

Maximum Allowable Pipe Span Length

Step 1: Variables Definition D - Pipe Outside Diameter [in]

W - Weight [lb/ft], includes water weight if hydrostatic testing is specified

MOAP - Maximum Allowable Operating Pressure [psi],

MOP - Maximum Operating Pressure [psi],

t - Pipe Wall Thickness [in]

SMYS - Specified Minimum Yield Strength or Grade of Steel [psi] ,

E - Modulus of Elasticity ( 29000 ksi )

H - Hoop Stress, [psi]

B - Bending Stress [psi]

M - Bending Moment [ft-lb]

L - Span Length [ft]

d - Deflection [in]

Step 2: Calculate Hoop Stress

Where P = MOP

Step 3: Calculate Maximum Allowable Bending Stress Solve Von Mises Equation through Quadratic Equation, and than solve for

Bending Stress B

Step 4: Calculate Maximum Allowable Bending Moment

Step 5: Calculate Maximum Span Length L, due to bending

Step 6: Calculate Maximum Span Length L, due to deflection

98

Important Notes : Maximum Operating Pressure (MOP) Must Be Less Then Maximum Operating Pressure

(MAOP)

Maximum Allowable Operating Pressure is calculated in accordance to DOT Code Part 192

using design factors



99

Blasting Analysis

SCOPE

This procedure describes the method for calculating the stresses caused by underground blasting

near an existing pipeline(s). The equations used follows guidelines set forth in CFR Title 49, Part

192.

BASIC CONSIDERATIONS

Blasting near an existing operating pipeline frequently occurs for a variety of reasons. Whenever

these underground explosion occur, they create circumferential and longitudinal stresses in

adjacent pipelines.

These stresses must be estimated to determine the possibility of damaging the pipelines.

This procedure describes the method for calculating the combined stresses on a pipeline in the

vicinity of blasting, those stresses being hoop stress due to internal pressure in the pipeline and

circumferential and longitudinal stresses due to blasting. In some instances, blasting may occur

near pipelines that are under the influence of circumferential and longitudinal stresses caused by

excessive backfill overburden (>10 Ft. of cover) or surface traffic. These situations require

special analysis and are not addressed in this standard procedure.

This procedure assumes that the blasting occurs at one location - a point charge. A blasting plan

may consists of a series of point charge blasts with a small delay between each blast. A biaxial

stress state exists when blasting occurs. These stresses are combined stress state.

Knowledge of soil (rock) conditions and construction methods is necessary to make sound

engineering judgements about each blasting situation. The following information is usually

required:

1. Description (trade name) of the explosive.

1. Method of detonation.

1. Delay time and weight of charge per delay.

1. Distance from pipeline.

1. Alignment Drawing No.and Survey Station or Mile Post.

1. Predominant rock type between the detonation point and the pipelines.

1. Diameter, wall thickness and SMYS of all pipelines in the vicinity of the blasting.

1. MAOP and the actual operating pressure of all pipelines in the vicinity of the blasting.

1. Class Location.

Frequently a series of blasts will be detonated with a small delay between each blast. It is

necessary to analyze the delay time with respect to seismic velocity to insure that each shock

100

wave arrives at the pipeline separately. In general, a minimum delay time of 25 milliseconds

(0.025 seconds) will assure that there is no compounding of shock waves. If seismic velocities

are low (1,000 - 2,500 ft./sec. ) a longer delay time may be required. Conversely, if delay times

are significantly less than 25 milliseconds, information about the expected seismic velocities

should be obtained. A sample calculation detailing the use of delay times and seismic velocities

is included with the example calculations.

II. EQUATIONS FOR CHARGE BLASTING ANALYSIS

The hoop stress due to internal pressure is calculated as follows:

The circuferential and longitudinal stresses caused by a point charge underground explosion are

calculated as follow:

The hoop stress and circumferential stress are combined as follows:

The combined stress level (S) is calculated as follow:

The longitudinal bending stress occurs in tension on the outside of the bend and in

compression on the inside of the bend. Tensile stress is represented with a positive value for ;

conversely, compressive stress takes a negative value for . The negative value for is used


101

when calculating the combined stress level (S). This will result in a larger ( more conservative)

combined stress level.

The allowable combined stress design factor (DFa) should be applied to the SMYS as follows:

S, psi < SMYS x DFa, where

S = Combined stress level, psi

SMYS = Specified Minimun Yield Strength of pipe, psi

DFa =Allowable Combined Stress Design Factor

The calculated combined stress design factor (DFc) should be determined as follows:

An unsafe blasting condition may be rectified in several ways. They include reducing the pounds

of explosive per delay, increasing the distance away from pipeline, using an explosive with a

lower energy release ratio, or reducing the pressure in the pipeline. It is normally impractical to

reduce the pipeline pressure.


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Bending Stress in Pipelines Caused by Fluid Flow Around Pipeline

S = bending stress, PSI

w = unit weight of fluid, pounds per cubic feet

@ 59 degree and 14.7 PSI:

air = 0.07651

water = 62.4

D =outside diameter of pipe, inches

d = inside diameter of pipe, inches

V = velocity of fluid, feet per second

L= length of pipe, feet

BENDING STRESS IN PILING

CAUSED BY FLUID FLOW

AROUND PILING

D = outside diameter of piling, inches



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THERMAL EXPANSION OF PIPELINES - LINEAR

E = elongation, in.

C = coefficient of linear expansion, inches per in per degrees F

L = length, feet

MATERIAL COEFFICIENT

steel 6.80E - 06

cast iron 6.60E - 06

copper 9.00E - 06

plastic 9.0E - 05

water 1.15E - 04

LONGITUDINAL STRESS

DUE TO TEMPERATURE CHANGES

S = stress, psi

E = modulus of elasticity, psi

C = coefficient of linear expansion, inches per inch per degrees F


104

Thrust at Blow-off


105

Steel Pipeline Crossings

API 1102 - PC PISCES

A.) PROGRAM SCOPE

API 1102 - PC PISCES (Personal Computer Pipeline Soil Crossing Evaluation System)

program is based on the design methodology resulting from the research and has been

implemented in the program to aid pipeline designers in analyzing existing uncased

pipelines and designing new uncased pipelines that cross beneath railroads and highways.

The details of the full design methodology can be found in “Technical Summary and

Database for Guidelines for Pipelines Crossing Beneath Railroads and Highways” (GRI-

91/0285, Final Report) and should have been read and understood. The design

methodology used in program follows directly the approach given in API RP 1102. Concise

summaries of the Cornell/GRI Guidelines are given in “Guidelines for Pipelines Crossing

Beneath Highways” (Stewart, et al., 1991b) and “Guidelines for Pipelines Crossing Beneath

Highways”. API RP 1102 should be available to the user for additional documentation and

preferences, and supplement the information provided by the program help and graphical

display of the design curves.

This design methodology relates to steel pipelines installed using trenchless construction

methods, in particular auger boring, with the crossing perpendicular to the railroad or

highway. The design methodology used in the program is such the pipelines having

diameters of D = 2 to 42 in. (51 to 1067 mm) can be analyzed. The wall thickness to

diameter ratios must be within the range of tw/D = 0.01 to 0.08.

Railroad crossings can be analyzed for depths of cover H = 6 to 14 ft (1.8 to 4.3 m).

Highway crossings can be analyzed for depth of cover H = 4 to 10 ft (in accordance with

API 1102) and H = 3 to 10 ft (PC-PISCES). The loading condition for railroads is based for

four axel distributed to the track surface, and would develop from the trailing and leading

axles sets form sequential cars. Highway loadings are based on both single and tandem-axle

truck loading configurations.

B.) LIST OF SYMBOLS

Bd - Bored diameter of crossing

Be - Burial factor for circumferential stress from earth load

D - Pipe outside diameter

E - Longitudinal joint factor

E' - Modulus of soil reaction

Ee - Excavation factor for circumferential stress from earth load

Er - Resilient modulus of soil

Es - Youngs modulus of steel

F - Design factor

Fi - Impact factor

FS1- Factor of safety for Seff

FS2 - Factor of safety for girth welds

FS3- Factor of safety for longitudinal welds

GHh- Geometry factor for cyclic circumferential stress from highway vehicular load

GHr - Geometry factor for cyclic circumferential stress from rail load

106

GLh - Geometry factor for cyclic longitudinal stress from highway vehicular load

GLr - Geometry factor for cyclic longitudinal stress from rail load

H - Depth to the top of the pipe

KHe - Stiffness factor for circumferential stress from earth load

KHh - Stiffness factor for cyclic circumferential stress from highway vehicular load

KHr - Stiffness factor for cyclic circumferential stress from rail load

KLh - Stiffness factor for cyclic longitudinal stress from highway vehicular load

KLr - Stiffness factor for cyclic longitudinal stress from rail load

L - Highway axle configuration factor

LG - Distance of girth weld from centerline

MAOP - Maximum allowable operating pressure

NH- Double track factor for cyclic circumferential stress

NL - Double track factor for cyclic longitudinal stress

Nt - Number of tracks at railroad crossing

Ps - Single axle wheel load

Pt - Tandem axle wheel load

P - Internal pipe pressure

R - Highway pavement type factor

RF- Longitudinal stress reduction factor for fatigue

Seff- Total effective stress

SFG- Fatigue resistance of girth weld

SFL - Fatigue resistance of longitudinal weld

SHe - Circumferential stress from earth load

SHi - Circumferential stress from internal pressure

SHiB - Circumferential stress from internal pressure calculated using the Barlow formula

S1- Maximum circumferential stress

S2- Maximum longitudinal stress

S3 - Maximum radial stress

SMYS - Specified minimum yield strength

T- Temperature derating factor

T1- Installation temperature

T2- Operating temperature

tw- Pipe wall thickness

w - Applied design surface pressure

T- Coefficient of thermal expansion

r- Unit weight of soil

SHh - Cyclic circumferential stress from highway vehicular load

SHr - Cyclic circumferential stress from rail load

SLh - Cyclic longitudinal stress from highway vehicular load

SLr - Cyclic longitudinal stress from rail load

s - Poissons ratio of steel

C. PROGRAM AND VARIABLES LIMITATIONS

C.1.) DIAMETER.

The diameter, D, is the outside pipe diameter, and has units of inches. The range of D is

2.0000 to 42.000 in. The default value is D = 12.750 in.

C.2.) MAXIMUM ALLOWABLE OPERATING PRESSURE, MAOP


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The maximum allowable operating pressure, MAOP, is used as the design internal pressure

for calculating circumferential stress due to internal pressurization, and has units of psi.

The range for MAOP is 0000 to 5000 psig.

C.3.) SPECIFIED MINIMUM YIELD STRENGTH, SMYS

The specified minimum yield strength, SMYS, has a range of allowable values covering

steel grades A25 (SMYS = 25000 psi) to X-80 (SMYS = 80000 psi). The SMYS is also used

to establish the girth and longitudinal weld fatigue endurance limits.

C.4.) DESIGN FACTOR, F

Although 49 CFR 192 or 195, establishes a design factor, F, the user can input another F

value. The range for F is from 0.10 to 1.00. The default design factor is F = 0.72.

C.4.) LONGITUDINAL JOINT FACTOR, E

The longitudinal joint factor, E, depends on the type of pipe welds. The input screen limits

E to either 0.60, 0.80, or 1.00, consistent with the values given in 49CFR192, Section

192.113. The default value is E = 1.00.

C.5.) INSTALLATION TEMPERATURE, T1

The installation temperature, T1 is given in F . This value is used with T2 to determine

thermal stress effects. The range of T1 is from -20 to 450 F.

C.6.) OPERATING TEMPERATURE, T2

The operating temperature, T2 is give in F. The T2 value is used to determine the

temperature derating factor, T. T2 also is used with T1 to determine thermal stress effects.

The range for T2 is from -20 to 450 F.

C.7.) WALL THICKNESS, tw

The pipe wall thickness, tw has units of inches. The wall thickness to diameter ratios must

be within the range of tw/D = 0.01 to 0.08.

C.8.) DEPTH OF CARRIER PIPE, H

The depth of the carrier pipe, H, given it ft, is measured from the top of tie to the pipeline

crown for railroads and from the top of pavement to the pipeline crown for highways. The

limits on H are:

6ft <= H <= 14 ft for railroads, and

4ft <= H <= 10 ft for highways (API 1102); 3ft <= H <= 10 ft for highways (PC-PISCES)

These are the depth limits for the live load design curves. The depth, H, also is used to

establish the impact factor, Fi used in the design methodology.

C.9.) BORED DIAMETER, Bd

The bored diameter, Bd (Bd in RP 1102), has units of inches. The minimum value is Bd =

D, and the maximum value is Bd = D + 6 in. The default value is Bd = D + 2 in.

C.10.) SOIL TYPE FOR THE EARTH LOAD

The soil type for the earth load calculations is either A or B. See Figure 4 in API RP 1102,

C.11.) MODULUS OF SOIL REACTION. E'

The modulus of soil reaction, E', has units of ksi. The minimum value allowed is E = 0.2 ksi,

and the maximum recommended value for auger bored installations is E = 2.0 ksi. The

maximum input value for E is 8.0 ksi. When an E value greater than 2.0 ksi is used, a

warning will be displayed that the value is beyond the normal range of E' for auger bored

installations. See details in API RP 1102.

C.12.) SOIL RESILIENT MODULUS, Er

The soil resilient modulus, Er has units of ksi. The minimum allowable value is Er = 5.00

ksi, and the maximum allowable value is Er = 20.0 ksi. These are the limits for the live load

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design curves. See Table 3 in API RP 1102 or The default value is Er = 10.0 ksi, as

recommended in API RP 1102.

C.13.) SOIL UNIT WEIGHT, r

The soil unit weight, r, has units of pcf, and can range from 0 to 150 pcf. The default value

is r = 120 pcf.

C.14.) TYPE OF LONGITUDINAL WELD

The type of longitudinal weld is used with the SMYS to establish the longitudinal weld

fatigue endurance limit, SFL. The choices for the type of longitudinal seam weld are SAW

or ERW. See Table 3 in API RP 1102 for the influence of longitudinal weld type and SMYS

on the seam weld fatigue endurance limits. The default type of longitudinal weld is SAW.

C15.) GIRTH WELD DISTANCE, LG (RAILROAD ONLY)

The girth weld distance, LG has units of ft and can range from 00 to 99 ft. The LG distance

is used to determine the longitudinal stress reduction factor, RF , needed for the girth weld

fatigue calculations. See Figure 18 A and 18 B in API RP 1102 for the RF values as

dependent on LG, H, and D. When a double track crossing is being analyzed, the

recommended value for LG is less than 5 ft. For LG less than 5 ft, longitudinal stress

reduction factors are not used.

C.16.) NUMBERS OF TRACKS, Nt (RAILROAD ONLY)

The number of tracks, Nt is used to determine whether a single or double track railroad

crossing will be analyzed. The Nt value determines the single or double track NH and NL

factors for circumferential and longitudinal live load pipelines stresses, respectively. The

default value is Nt = 1.

C.17.) E - TYPE RAIL LOADING (RAILRAOD ONLY)

The E - Type rail loading is used to determine the applied surface stress, w, for railroad

crossings. The range for the E type lading is from E - 00 to E - 99. can also be entered,

which causes the surface load, w, to be 1.0 psi. The default value is E - 80 loading, as

recommended in API RP 1102.

C.18.) DESIGN SINGLE WHEEL LOAD, Ps (HIGHWAY ONLY)

The design single wheel load, Ps , has units of kips, and can range from 0.00 to 20.0 kips.

The pavement type, design wheel loads, diameter, and depth are used to establish the

pavement type factor, R, and axle configuration factor, L. The default value is Ps = 12.0

kips, as recommended in API RP 1102.

C.19.) DESIGN TANDEM WHEEL LOAD, Pt (HIGHWAY ONLY)

The design tandem wheel load, Pt (, has units of kips, and can range from 0.00 to 20.0 kips.

The pavement type, design wheel loads, diameter, and depth are used to establish the

pavement type factor, R, and axle configuration factor, L. The default value is Ps = 10.0

kips, as recommended in API RP 1102.

C.20.) PAVEMENT TYPE (HIGHWAY ONLY)

The pavement type for highway crossings can be either flexible , none, or rigid . The

pavement type, design wheel loads, diameter and depth are used to establish the pavement

type factor, R, and axle configuration factor, L. The default pavement type is flexible.

C.21.) YOUNGS MODULUS, Es

Youngs modulus of the steel carrier pipe, Es (Es in RP 1102), has units of ksi. The range is

from 29 000 to 31 000 ksi. The default value is Es = 30 000 ksi.

C.22.) POSSIONS RATIO, s


109

Possions ratio of the steel carrier pipe, s , is used to assess thermal and longitudinal

stresses due to the circumferential earth load and internal pressure stresses. The allowable

range is from 0.25 to 0.30. The default value is s = 0.30.

C.23.) COEFFICIENT OF THERMAL EXPANSION, T

The coefficient of thermal expansion of the steel carrier pipe T , is given for temperature

is F, and is used to assess longitudinal thermal stresses. The range is from 0.0000060 to

0.0000080 per F. The default value is T = 0.0000065 per F.

D. DESIGN CURVES

110


111

112


113

114


115

116


117

118


119

120


121

122



123

Wheel Load Analysis

SCOPE:

The Wheel Load Analysis Program was designed to calculate the overburden and vehicle

loads on buried pipe with a Single Layer System (soil only) or a Double Layer Systems

(timbers, pavement and soil). The information used to design this program was taken from

the Battelle Petroleum Technology Report on "Evaluation of Buried Pipe Encroachments"

which considered the theoretical work done by M.G. Spangler on overburden and vehicle

loads on buried pipe.

REQUIRED INFORMATION:

1. Values for all of the following variables:

H - cover, vertical depth from the ground to the top of the pipe (ft.)

B - trench width (ft.)

Ds - weight per unit volume of backfill (lbs./ft.³)

D - outside diameter of the pipe (in.)

Lw - concentrated surface load (lbs.) (Wheel Load) (see Section 4, Page 11)

H1 - thickness of the pavement layer (in.) (see Figure 2)

SMYS - specified minimum yield stress of the pipe (psi.)

P - pipe internal pressure (psi.)

T - pipe wall thickness (in.)

2. The Design Class of the pipeline being analyzed (1-3) which is used to find the

Maximum Allowable Combined Stress (% SMYS), see Table I.

3. The Soil Type which is used to find the friction force coefficients (Km), see Table II.

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4. The Pavement Type which is used to find the impact factor (I), see Table III, and the

elastic constants for layered media analysis (E1, E2, G1, & G2), see Table IV &

Figure 2.

5. The Crossing Construction Type which is used to find the bedding constants for

buried pipe (Kb & Kz), see Table V & Figure 3.

REQUIRED INFORMATION IF LONGITUDINAL BENDING STRESS OCCURS:

6. All the above information along with values for the following variables:

X - longitudinal distance over which deflection occurs (ft.)

Y - vertical deflection (in.)

Table I


125

Maximum Allowable Combined Stress

Maximum Maximum

Design Operating Allowable Allowable

Class Class Internal Combined

Stress Stress

(%) (%)

1. 1. 72 80

1. 72 80

2 2 62 72

2 3. 62 72

3 3 50 62

3 4. 50 62

Figure 1 shows a cross sectional view of a pipe buried in a trench. As a first estimate of the

soil load on the pipe it could be assumed that the backfill soil slides down the trench walls

without friction. Additionally assume that all soil above the pipe is supported by the pipe

itself and that the backfill soil on either side of the pipe does not assist in this support.

These assumptions are very conservative but they help a great deal in initial understanding

of the method of solution. The assumptions yield a soil load on the pipe equal to the weight

of the backfill soil above the pipe. This analysis provides an estimate of soil loads on the

buried pipe if nothing else is known about the system.

The basic analysis developed by M.G. Spangler follows similar arguments to that given

above. In this analysis, Spangler includes frictional forces between the trench wall and the

backfill. This permits the weight of the overburden to be partially carried by the

surrounding soil and reduces the total soil load on the pipe. The resulting equations for

calculating the pipe load due to overburden are as follows:

Cd - trench coefficient.

B - trench width (ft.).

H - cover, vertical depth from the ground to the top of the pipe (ft.).

Km - coefficient of friction force between the backfill soil and the trench wall.

Cd determines how much load is carried by the pipe. If there is no soil friction Cd becomes

equal to H/B and the entire backfill load must be supported by the pipeline.

The term Km provides a coefficient of friction force between the backfill soil and the

trench wall. A high value of Km implies that friction between the backfill and trench wall is

high and the weight of the backfill is supported largely by the wall friction. A low value

implies that there is little friction encountered and the backfill is allowed to settle more

such that the weight must be supported by the pipe. Table II provides values of Km used in

the program for five different soil types. Also in Table II are examples of values for Ds, the

126

density which is the weight per unit of backfill, which may be used if an actual value is not

known. Note: If a value for Ds is already given use that value instead of the one in Table II.

Table II

Friction Force Coefficients For Various Soils

Soil Type Km Ds

(lbs/ft³)

(1) Granular Materials without Cohesion 0.1924 90-100

(2) Sand and Gravel 0.165 110-120

(3) Saturated Top Soil 0.150 110-120

(4) Clay 0.130 110-120

(5) Saturated Clay 0.110 120-130

The soil types and coefficients given in this table represent the range that could normally

be expected. Saturated clay has little internal friction so that it has the smallest value for

Km. This implies that almost all of the soil load is carried by the pipe. Granular materials

have a great deal more internal friction. Their value of Km is higher which leads us to the

conclusion that the pipe carries less of the backfill load. Spangler, in his work, recommends

using the value for clay in most instances. Higher values may be used when there is

adequate evidence that the internal friction is higher and warrants a higher value of Km.

Spangler's recommendation provides a conservative estimate for common buried pipe

situations. Marsh and bog areas, however, have friction properties more similar to

saturated clay such that a value for Km equal to 0.110 should be used in these areas.

Wc - load per unit length of the pipe due to overburden (lbs./in.).


Ds - density which is the weight per unit of backfill (lbs./ft.³).



A Pavement Type must be determined in order to select an Impact Factor (I) to be used in

the Wv equation. Table III provides Impact Factor values for the three different pavement

types used in this program. A Pavement Type is also used to select the elastic constants for

layered media analysis. The variables E1 & G1 will be used to represent the elastic

constants for the top layer and E2 & G2 will be used to represent the elastic constants for

the soil. See Figure 2 for a visual explanation of the elastic constants for the top layer and

the soil. These values will also be used in the Wv equation. Table IV provides the values for

the three different pavement materials used in this program.

Table III

Impact Factor

Pavement Type Factor

(I)

No Pavement 1. 5


127

Asphalt 1. 3

Timber Mats (2" x 12" minimum) 1.2

Concrete 1.0

Wv - average load per unit length of pipe for vehicular load (lbs./in.).

D - outside diameter of the pipe (in.).

E1 - modulus of elasticity of the top (timber or pavement) layer (lbs./in.²).

E2 - modulus of elasticity of the soil cover (lbs./in.²).

G1 - Poisson's ratio of the top (timber or pavement) layer.

G2 - Poison's ratio of the soil cove

H - thickness of the pavement layer plus the depth of the soil from the pavement interface

to thetop of the pipe (ft.). (See Figure 2)

H1 - thickness of the pavement layer ("0" is used when there is no pavement) (in.).

H2 - depth of the soil from the pavement interface to the top of the pipe (ft.).

I - impact factor.

Lw - concentrated surface load (a value of 16,000 lbs. is recommended when the maximum

is unknown), wheel load in lbs..

Examination of equation Wv shows that this equation also may be used with a Single Layer

System because the Pavement Material on the Top Layer chosen is "Soil", which makes E1

equal to E2, G1 equal to G2, and H1 equal to zero which cancels out the second and third

part of the equation. Thus when there is no pavement layer the revised equation will

provide a solution for soil cover only. Table IV provides the values for E1, E2, G1 & G2

that will be used in the program.

Table IV

Elastic Constants for Layered Media Analysis

Pavement E

Material (psi.) G

(1) No Pavement (Soil Only) 1. 5 x 104 0.35

(2) Asphalt 1. 0 x 105 0.40

(3) Timber Mats (2" x 12" 1. 2 x 106 0.25

(4) Concrete 2. 0 x 10 6 0.15

Sc - circumferential stress due to pipe wall deflection (PSI).


E - pipe material modulus of elasticity (2.9 x 107).

128

Kb - bending coefficient which is a function of the crossing construction types.

Kz - deflection coefficient which is a function of the crossing construction types.

P - pipe internal pressure (PSI).

T - pipe wall thickness (in.).

Wc - load per unit length of pipe due to overburden (lbs./in.).

Wv - average load per unit length of pipe for vehicular load (lbs./in.).

Note that the equation Sc includes pressure in the denominator so that bending stresses are

reduced by increasing pressure.

Equation Sc, as well as equation St, have two constants which depend upon the bedding

material upon which the pipe is placed. This bedding material is based on the crossing

construction type. When the pipe is placed on a rigid bedding such as an Open Cut-Rock,

little soil deformation occurs so that the load application area on the bottom is very small.

However if the pipe is placed on soil, the support conforms to the pipe somewhat and the

load is distributed over a larger area (See Figure 3). The latter case produces less pipe

stress and is preferable. Spangler's formulation includes both of these possibilities in order

to provide a conservative estimate for the rigid bedding case without penalizing the soil

bedding case. It does so by varying the constants Kb and Kz. Spangler's recommended

values for the constants are provided in Table V.

Table V

Bedding Constants for Buried Pipe

Width of

Uniform Crossing

Soil Reaction Construction

(Degrees) _ Type Kz Kb

0 (1) Open Cut-Rock 0.110 0.294

30 (2) Open Cut 0.108 0.235

90 (3) Bored 0.096 0.157

Sh - hoop stress due to internal pressure (PSI).




St is the total circumferential stress in the pipe wall due to pressure (hoop) stress and

bending stresses resulting from circumferential flexure caused by external loads measured

in PSI. The first term on the right hand side of the equation is the formula for hoop stress

due to internal pressure (Sh) and the second term is the formula for circumferential stress

due to pipe wall deflection (Sc).

Longitudinal Bending Stress (Sb) is when the overburden and vehicle loads on buried

pipelines will cause pipe settlement into the soil in the bottom of the trench. This settlement

occurs because soil is not as stiff as the pipe and will deform easily as the pipe is "pushed"

downward. Under uniform soil conditions and overburden loading, the pipe will settle


129

evenly into the trench bottom along its entire length. Soil is not generally uniform,

however, and regions of "softer" soil will occur adjacent to regions of stiff soil, so that the

pipe will settle unevenly and hence bending will occur. A load that is applied on only one

portion of a pipeline will cause the section of pipe under the load to settle more than the

unloaded pipe, such that bending will also result. Longitudinal bending stress occurs in

tension on the outside of the bend and in compression on the inside of the bend. Tensile

stress is represented with a positive value for Sb; conversely, compressive stress takes a

negative value for Sb. The longitudinal bending stress is calculated as follows:

Sb - longitudinal bending stress (PSI).



X - longitudinal distance over which deflection occurs (ft.).

Y - vertical deflection (in.).

A negative value will be used when calculating the total combined stress (S). This will result

in a larger (more conservative) combined stress. Note: If longitudinal bending stress does

occur, click onto the designated box next to "Longitudinal Bending Stress" . If the box is

not marked then the program will assume "0" for Sb.

S - total combined stress by Von Mises (PSI).


St - total circumferential flexure caused by external loads (PSI).

Note that if longitudinal bending stress is not present then the S will equal St.

The final calculation is % SMYS. This is calculated to determine if the current conditions

exceed the Maximum Allowable Combined Stress determined by Transcontinental Gas

Pipe Line Corporation.


SMYS - specified minimum yield stress of the pipe (PSI).

References:

ASME B31.8 "Gas Transmission and Distribution Systems"

"Evaluation of Buried Pipe Encroachments", BATTELLE, Petroleum Technology Center,

1983


130

Track Load Analysis

SCOPE:

The Track Load Program was designed to calculate the overburden and track loads on

buried pipe with a Single Layer System (soil only). The information used to design this

program was taken from the Battelle Petroleum Technology Report on "Evaluation of

Buried Pipe Encroachments" which considered the theoretical work done by M.G.

Spangler on overburden and vehicle loads on buried pipe.

REQUIRED INFORMATION:

1. Values for all of the following variables:

H - cover, vertical depth from the ground to the top of the pipe (ft.)

B - trench width (ft.)

Ds - weight per unit volume of backfill (lbs./ft.³)

D - outside diameter of the pipe (in.)

SMYS - specified minimum yield stress of the pipe (psi.)

P - pipe internal pressure (psi.)

T - pipe wall thickness (in.)

2. Values for the following information about the track:

Lt - operating weight of the object crossing the pipeline with tracks (lbs.)

Tw - width of standard track shoe (in.)

Tl - length of track on the ground (ft.)

Tg - track gauge (ft.)

3. The Design Class of the pipeline being analyzed (1-3) which is used to find the

Maximum Allowable Combined Stress (% SMYS), see Table I.

4. The Soil Type which is used to find the friction force coefficients (Km), see Table II.

5. The Crossing Construction Type which is used to find the bedding constants for

buried pipe (Kb & Kz), see Table V & Figure 3.


131

REQUIRED INFORMATION IF LONGITUDINAL BENDING STRESS OCCURS:

6. All the above information along with values for the following variables:

X - longitudinal distance over which deflection occurs (ft.)

Y - vertical deflection (in.)

In compliance with the Transcontinental Gas Pipe Line Corporation specification on Road

Crossing Analysis Procedure, the following table will be used to determine the maximum

allowable stress for a particular design class which will be given as a variable:

Table I

Maximum Allowable Combined Stress

Maximum Maximum

Design Operating Allowable Allowable

Class Class Internal Combined

Stress Stress

(%) (%)

1. 1. 72 80

1. 72 80

2 2 62 72

2 3. 62 72

3 3 50 62

3 4. 50 62

132

As a first estimate of the soil load on the pipe it could be assumed that the backfill soil

slides down the trench walls without friction. Additionally assume that all soil above the

pipe is supported by the pipe itself and that the backfill soil on either side of the pipe does

not assist in this support. These assumptions are very conservative but they help a great

deal in initial understanding of the method of solution. The assumptions yield a soil load on

the pipe equal to the weight of the backfill soil above the pipe. This analysis provides an

estimate of soil loads on the buried pipe if nothing else is known about the system.

The basic analysis developed by M.G. Spangler follows similar arguments to that given

above. In this analysis, Spangler includes frictional forces between the trench wall and the

backfill. This permits the weight of the overburden to be partially carried by the

surrounding soil and reduces the total soil load on the pipe. The resulting equations for

calculating the pipe load due to overburden are as follows:

Cd - trench coefficient.




Cd determines how much load is carried by the pipe. If there is no soil friction Cd becomes

equal to H/B and the entire backfill load must be supported by the pipeline.

The term Km provides a coefficient of friction force between the backfill soil and the

trench wall. A high value of Km implies that friction between the backfill and trench wall is

high and the weight of the backfill is supported largely by the wall friction. A low value

implies that there is little friction encountered and the backfill is allowed to settle more

such that the weight must be supported by the pipe. Table II provides values of Km used in

the program for five different soil types. Also in Table II are examples of values for Ds, the

density which is the weight per unit of backfill, which may be used if an actual value is not

known. Note: If a value for Ds is already given use that value instead of the one in Table II.

Table II

Friction Force Coefficients For Various Soils

Soil Type Km Ds

(lbs/ft³)

(1) Granular Materials without Cohesion 0.1924 90-100

(2) Sand and Gravel 0.165 110-120

(3) Saturated Top Soil 0.150 110-120

(4) Clay 0.130 110-120

(5) Saturated Clay 0.110 120-130

The soil types and coefficients given in this table represent the range that could normally

be expected. Saturated clay has little internal friction so that it has the smallest value for

Km. This implies that almost all of the soil load is carried by the pipe. Granular materials

have a great deal more internal friction. Their value of Km is higher which leads us to the

conclusion that the pipe carries less of the backfill load. Spangler, in his work, recommends

using the value for clay in most instances. Higher values may be used when there is

adequate evidence that the internal friction is higher and warrants a higher value of Km.


133

Spangler's recommendation provides a conservative estimate for common buried pipe

situations. Marsh and bog areas, however, have friction properties more similar to

saturated clay such that a value for Km equal to 0.110 should be used in these areas.

Wc - load per unit length of the pipe due to overburden (lbs./in.).


Ds - density which is the weight per unit of backfill (lbs./ft.³).



The Impact Factor (I) for a track load calculation with a single layer system is always going

to be 1.5. The reason for this is that the impact factor for soil is 1.5 and that is the only

thing that separates the track from the pipe in a single layer system.

Calculating track load is somewhat different from calculating a wheel load because the

load of a track expands over a larger area rather than a single point as does the wheel load.

The information needed from the track are the operating weight (Lt) of the object crossing

the pipeline with tracks is measured in lbs., the width of the standard track shoe (Tw)

measured in inches, the length of the track on the ground (Tl) measured in ft., and the

track gauge (Tg) measured in ft .

The weight of a track can be considered as a uniformly distributed load applied at the top

of the soil over an area equal to the length of the track on the ground times the width of the

standard track shoe. On the basis of this assumption, the unit pressure at a point on the top

of the line pipe or casing pipe directly beneath the center of the area may be estimated by

means on Newmarks Integration of Boussinesq equation. Newmark determined the

pressure at a point in the undersoil at any elevation below one corner of the rectangular

area over which unit loads are uniformly applied, and gave influence coefficients

corresponding to the Influence Factor m and Influence Factor n.


Tw - width of standard track shoe (in.).


Tl - length of the track on the ground (ft.).

These two factors are used by M.G. Spangler in the table called "Influence Coefficients for

Solution of Holl's and Newmark's Integration of the Boussinesq Equation for Vertical

Stress", see Table VI. Both of the influence factors will be rounded off to the nearest 0.01 in

order to cross reference Table VI.

134

Qd - maximum static pressure on the pipe directly under the center of the object with

tracks

(lbs./ft.²).

Ic - Influence Coefficient selected from Table VI.

Lt - operating weight of the object crossing the pipeline with tracks (lbs.)

Tl - length of the track on the ground (ft.).

Tw - width of standard track shoe (in.).

The equation for Qd is widely employed in structural work to estimate the unit pressure on

a deep soil stratum below a foundation, it appears to be appropriate for this problem. The

constant equal to 0.5 will be multiplied by Lt to get the operating load of one track.

Wt - total track load on the pipe (lbs./in.).


I - impact factor of 1.5.

Qd - calculated result from equation Qd (lbs./ft.²).

Dividing the part of the equation (I * Qd) by twelve gives the load per linear inch of pipe.

Dividing the outside diameter of the pipe by twelve converts D, which is measured in

inches, into units of feet.

Sc - circumferential stress due to pipe wall deflection (PSI).



Kb - bending coefficient which is a function of the crossing construction types.


135

Kz - deflection coefficient which is a function of the crossing construction types.



Wc - load per unit length of pipe due to overburden (lbs./in.).

Wt - total track load on the pipe (lbs./in.).

Note that the equation Sc includes pressure in the denominator so that bending stresses are

reduced by increasing pressure.

Equation Sc, as well as equation St, have two constants which depend upon the bedding

material upon which the pipe is placed. This bedding material is based on the crossing

construction type. When the pipe is placed on a rigid bedding such as an Open Cut-Rock,

little soil deformation occurs so that the load application area on the bottom is very small.

However if the pipe is placed on soil, the support conforms to the pipe somewhat and the

load is distributed over a larger area (See Figure 3). The latter case produces less pipe

stress and is preferable. Spangler's formulation includes both of these possibilities in order

to provide a conservative estimate for the rigid bedding case without penalizing the soil

bedding case. It does so by varying the constants Kb and Kz. Spangler's recommended

values for the constants are provided in Table V.

Table V

Bedding Constants for Buried Pipe

Width of

Uniform Crossing

Soil Reaction Construction

(Degrees) _ Type Kz Kb

0 (1) Open Cut-Rock 0.110 0.294

30 (2) Open Cut 0.108 0.235

90 (3) Bored 0.096 0.157

Sh - hoop stress due to internal pressure (PSI).




St is the total circumferential stress in the pipe wall due to pressure (hoop) stress and

bending stresses resulting from circumferential flexure caused by external loads measured

in PSI. The first term on the right hand side of the equation is the formula for hoop stress

due to internal pressure (Sh) and the second term is the formula for circumferential stress

due to pipe wall deflection (Sc).

Longitudinal Bending Stress (Sb) is when the overburden and vehicle loads on buried

pipelines will cause pipe settlement into the soil in the bottom of the trench. This settlement

occurs because soil is not as stiff as the pipe and will deform easily as the pipe is "pushed"

downward. Under uniform soil conditions and overburden loading, the pipe will settle

evenly into the trench bottom along its entire length. Soil is not generally uniform,

136

however, and regions of "softer" soil will occur adjacent to regions of stiff soil, so that the

pipe will settle unevenly and hence bending will occur. A load that is applied on only one

portion of a pipeline will cause the section of pipe under the load to settle more than the

unloaded pipe, such that bending will also result. Longitudinal bending stress occurs in

tension on the outside of the bend and in compression on the inside of the bend. Tensile

stress is represented with a positive value for Sb; conversely, compressive stress takes a

negative value for Sb. The longitudinal bending stress is calculated as follows:




X - longitudinal distance over which deflection occurs (ft.).

Y - vertical deflection (in.).

A negative value will be used when calculating the total combined stress (S). This will result

in a larger (more conservative) combined stress. Note: If longitudinal bending stress does

occur, click onto the option box. If the box is not marked then the program will assume "0"

for Sb.



St - total circumferential flexure caused by external loads (PSI)

Note that if longitudinal bending stress is not present then the S will equal St.

The final calculation is % SMYS. This is calculated to determine if the current conditions

exceed the Maximum Allowable Combined Stress determined by Transcontinental Gas

Pipe Line Corporation.


SMYS - specified minimum yield stress of the pipe (PSI).

References:

ASME B31.8 "Gas Transmission and Distribution Systems"

"Evaluation of Buried Pipe Encroachments", BATTELLE, Petroleum Technology Center,

1983



137

Design of Uncased Pipeline Crossings

This method is proven and acceptable and can be used in the cases when the crossing

conditions for design are out of the scope and the limitations of API RP 1102 and PC-

PISCES.

Reference: GPTC Guide for Transmission and Distribution Systems, A.G.A.


139

Pipeline Testing & Miscellaneous

API 1104 - Appendix A: Weld Imperfection Assessment

Please see API Standard 1104, Welding of Pipelines and Related Facilities, Appendix A,

Option 2 for the background of the assessment procedure.


140

API 1104 - Appendix A: Weld Imperfection Assessment

Please see API Standard 1104, Welding of Pipelines and Related Facilities, Appendix A,

Option 2 for the background of the assessment procedure.



141

Gas Pipeline Pressure Testing - Maximum Pressure Drop


142

NiSource Blowdown Calculations

The details of calculation procedure for this application are provided in electronic

document SWRI Report No. 87-2 and can be accessed by clicking the button “SWRI

Report No. 87-2”.



143

Purging Calculations

Method "A"

1. Find flow rate through the blow-off valve by using the formula for critical velocity,

Q = K

where Q = flow rate, MSCFH

K = flow coefficient, MSCF/(h x psi absolute)

P2 = pressure just upstream of blow-off valve, psi

2. From rearranged Weymouth formula to find an estimate pressure value of necessary to

maintain this flow rate:

3. Recommended purge time is 2T. The minimum purge time in minute is

or

where D = inside diameter of pipe, in

L = length of purge section, mi

C

C = (0.0361)D (1-h Weymouth coefficient in MSCF/h x mi)

Pm = average pressure, psi absolute

P1 = pressure at upstream end of section, psi absolute

P 2= pressure at downstream end of section, psi absolute (just

upstream of blow-off valve)

K = 1-h blow-off coefficient for standard blow-off sizes,

MSCF/ ( h x psi absolute)

One-Hour-Blow-off Coefficient for Standard Blow-off Sizes: Blow-off size, in. K, MSCF /(h x psi absolute)

144

1 0.75

2 3.0

3 6.0

4 13.5

6 24.0

8 47.0

10 72.0

where c = conversion constant = 60/14.73 = 4.07

V = actual volume of pipe section purged, thousand ft , where

pipe section is assumed to be filed with air prior to purge

K = blow-off coefficient, MSCF /(h x psi absolute)


P1 = pressure at downstream end of section, psi absolute, just

upstream of blow-off valve

The volume of gas lost, MSCF, is

where V = actual volume of pipe action purged, thousand ft ,where

pipe section is assumed to be filled with air prior to purge;

equal to (0.028798)D , D in inches, L in miles


P2 = pressure at downstream end of section, psi absolute

( just upstream of blow-off valve)

C , with C = (0.0361)D , D in inches, L in miles

K = 1-hour blow-off coefficient for standard blow-off sizes,

MSCF/(h x psi absolute)

Method "B"

where V = actual volume of pipe purged, thousand ft , where

pipe section is assumed to be filled with air prior to purge;

equal to(0.028798)D L, D in inches, L in miles

P = pressure of downstream end of section, psi absolute

( just upstream of blow-off valve)

t = actual time of purge, minutes

K = 1-h blow-off coefficient for standard blow-off sizes,

MSCF/ (h x lb/in absolute)



145

Pack in Pipeline

Pack in pipeline - Isolated pipe section Gas packed in isolated section of the pipeline can be calculated in the same way where,

P1 = P2 = Ps

146

Compressibility factor Z is calculated using procedure from Engineering Data Book, Volume II,

Gas Processor Association, Revised Tenth Edition, 1994

References:

1. Pipeline Design for Hydrocarbons Gases and Liquids, Committee of pipeline planning,

American Association of Civil Engineers, 1975

2. Engineering Data Book, Volume II, Gas Processor Association, Revised Tenth Edition,

1994

3. Pipeline Design & Construction, A Practical Approach, American Society of Mechanical

Engineers, 2000


147

Pipeline Corrosion

EVALUATION OF MAOP IN CORRODED AREAS - ANSI B.31.G -1991

Computation of A

If the measured maximum depth of the corroded area is greater than 10 % of the nominal wall

thickness, and the measured longitudinal extent of the corroded area is greater than the value

determined by Equation (2), calculate:

where

Lm = measured longitudinal extent of the corroded area(inches).

D = nominal outside diameter of the pipe(inches).

t = nominal wall thickness of the pipe, in. Additional wall thickness required

for concurrent external loads shall not be included in calculation.

COMPUTATION OF P’

(a) For values of Less Than or Equal to 4.0.

where

= the safe maximum pressure for the corroded area

d = measured maximum depth of corroded area, in.

may not exceed P

P = the greater of either the established MAOP or

Where

S = specified minimum yield strength (SMYS), psi

F = appropriate design factor from ASME B31.4, ASMEB31.8, or ASME B31.11

T = temperature derating factor from the appropriate B31 Code(if not listed, T = 1)


T = nominal wall thickness of the pipe(inches). Additional wall thickness required

for concurrent external loads shall not be included in the calculations.

(b) For Value of A Greater Than 4.0

MAOP and

If the established MAOP is equal to or less than , the corroded region may be used for service at

that MAOP. If the established MAOP is greater than , then a lower MAOP should be established

not to exceed , or the corroded region should be repaired or replaced.


148

DETERMINATION OF MAXIMUM ALLOWABLE LONGITUDINAL EXTENT OF

CORROSION - ANSI B.31.G - 1991

The depth of a corrosion pit may be expressed as a percent of nominal wall thickness of pipe by:

% pit depth = 100 (1)

where

d = measured maximum depth of the corroded area(inches).

t = nominal wall thickness of pipe(inches). Additional wall thickness required for concurrent

external loads shall not be included in the calculation.

A contiguous corroded area having a maximum depth of more then 10 % but less than 80 % of

the nominal wall thickness of the pipe should not extend along the longitudinal axis of the pipe

for a distance greater than that calculated from:

(2)

where

L = maximum allowable longitudinal extent of the corroded area(inches).


B = a value which may be determined from :

(3)

except that B may not exceed the value 4. If the corrosion depth is between 10% and 80%, use B

= 4.0 in Equation (2).


Pipeline Corrosion

149

Rate of Electrical Current Flow Through the Corrosion Cell


150

Relationship Between Resistance and Resistivity


Pipeline Corrosion

151

Electrolyte Resistance from the Surface of an Electrode to any Distance


152

Ohm's Law for Corrosion Current


Pipeline Corrosion

153

Electrical Resistance of a Conductor


155

Cathodic Protection

Estimated Life of a Magnesium Anode


156

Resistance to Earth of an Impressed Anode Ground Bed


Cathodic Protection

157

Rudenberg Formula

Vx - Potential at x in volt caused by grounds anode current

I - Ground anode current in amperes

- Earth resistivity in ohm-centimeters

y - Length of anode in earth in feet

x - distance from ground anode in feet

If x greater then 10y then,


158

Single Vertical Anode Resistance to Earth and Typical Installation

R - Anode resistance to earth [ohm]

- Soil resistivity [ohm-cm]

L - Anode length [ft.]

d - Anode diameter [ft.]

s - Anode spacing in feet

h - Earth surface - Anode [ft.]


Cathodic Protection

159

Resistance to Earth of Multiple Vertical Anodes in Parallel





N - Number of anodes in parallel




160

Single Horizontal Anode Resistance to Earth and Typical Installation








Cathodic Protection

161

Required Number of Anodes and Total Current Requirement


162

Cathodic Protection Attenuation Calculation

Cathodic Protection

163

For typical pipeline with multiple drain points (anodes) with uniform spacing of 2L The

potential and current are given:

Reference:

1. Uhlig's Corrosion Handbook (2nd Edition) Edited by: Revie, R. Winston © 2000

John Wiley & Sons

2. ISO 15589-2 Petroleum and Natural gas Industries Cathodic Protection Pipeline

Transportation Systems

3. Pipeline Corrosion and Cathodic Protection, Third Edition, Gulf Publishing

Company


164

Power Consumption of a Cathodic Protection Rectifier

Note : The formula is approximate, and based on 48% efficiency of rectifier.


165

Polyethylene Pipe Design and Pipeline

Crossings

Dead Load on PE Pipe - Prism, Marston and Combined

Load

A. Prism Load

B . Marston Load (ASCE Manual No.60)

Typical Value for

Soil Typical Value for

Saturated clay 0.110

Ordinary clay 0.130

Saturated top soil 0.150

Sand and gravel 0.165

166

Clean granular soil 0.192

C. Combined Prism and Marston Load

For flexible pipe, a more conservative method is to use a soil pressure load in between

prism and Marston load:

Reference:

1. “Soil Engineering”, Third Edition, Spangler, M.G. and Handy, R.L., Intext

Educational Press

2. “Structural Mechanics of Buried Pipes”, Watkins, R.K, and Loren, R, A,

3. “Polyethylene Pipe Handbook: Design of PE Piping Systems”, Second Edition,

Plastic Pipe Institute, Inc.


Polyethylene Pipe Design and Pipeline Crossings

167

Spangler's Modified Iowa Formula for PE Pipe

Reference:


Educational Press





168

Modulus of Soil Reaction (E') - Average Values for Iowa

Formula

Reference: “Modulus of Soil Reaction Values for Buried Flexible Pipe”, Journal of the

Geotechnical Engineering Division, ASCE, Vol. 103, No GT 1, Howard, A.K.



169

Modulus of Soil Reaction (E') - Values of E' for Pipe

Embedment

Reference:

“Evaluation of Modulus of Soil Reaction E and its Variation with Depth”, Report No.

UCB/GT/82-02,


170

Values of E'n Native Soil Modules of Soil Reaction



171

Soil Support Factor (Fs)

Reference:

“Polyethylene Pipe Handbook: Design of PE Piping Systems”, Second Edition, Plastic Pipe

Institute, Inc.


172

Pipe Wall Compressive Stress (PE Pipe Crushing)

Reference:





173

Distributed Static Surcharge Load Directly over Buried PE

Pipe

1. Dead/Earth Load

A. Prism Load



174



2. Distributed Static Surchage Load

This method is using Boussinesq equation for pressure acting on pipe crown.

Influence coefficient is selected from the table below:


175

3. Pipe Deflection is calculated using Spangler's Modified Iowa Formula:

4. Pipe Wall Compressive Stress

176

Reference:


Educational Press






177

Distributed Static Surcharge Load not over Buried PE Pipe

1. Dead/Earth Load

A. Prism Load



178



2. Distributed Static Surchage Load not over PE Pipe

This method is using Boussinesq equation for pressure acting on pipe crown.


179

Influence coefficient is selected from the table below:


180


Reference:


Educational Press






181

Live Load: Aircraft Load on Buried PE Pipe

1. Dead/Earth Load

A. Prism Load



182



2. Live Load: Aircraft Load on Buried PE Pipe



183


Reference:

184


Educational Press





185

Index

A

A.G.A - Fully Turbulent Flow .................. 47

AccidentalFullBore ................................... 40

AccidentalSmallHole ................................ 37

Adobe .......................................................... 1

API 1102 - Steel Pipelines Crossing

Railroads and Highways ..................... 105

API 1104 - Appendix A

Weld Imperfection Assessment .. 139, 140

API 1117 - Movement of In-Service

Pipeline ................................................. 86

B

Blasting Analysis ...................................... 99

Buoyancy Analysis and Concrete Coating

Thickness .............................................. 92

Buoyancy Analysis and Concrete Weight

Spacing .................................................. 94

Bureau of Reclamation Average E' Values

for Iowa Formula ................................ 168

C

Cathodic Protection Attenuation Calculation

............................................................. 162

Centrifugal Compressor - Adiabatic Head 23

Centrifugal Compressor - Fan Laws ......... 29

Centrifugal Compressor - Required

Adiabatic Horsepower .......................... 25

Centrifugal Compressor - Required

Polyitropic Horsepower ........................ 27

Colebrook - White..................................... 48

Compressor Station Piping - Diameter and

Gas Velocity.......................................... 34

D

Dead Load on PE Pipe - Prism, Marston and

Combined Load ................................... 165

Design Pressure - Plastic Pipe............. 64, 65

Design Pressure - Steel Pipe ... 57, 58, 62, 63

Discharge Temperature ............................. 33

Distributed Static Surcharge Load not over

PE Pipe ................................................ 178

Distributed Static Surcharge Load over PE

Pipe ..................................................... 173

E

Electrical Resistance of a Conductor ...... 153

Electrolyte Resistance from the Surface of

an Electrode to any Distance............... 151

Estimated Life of a Magnesium Anode .. 155

F

Flume Design ............................................ 67

186

G

Gas Pipeline Pressure Testing - Maximum

Pressure Drop ...................................... 141

Gas Properties Calculations ........................ 9

GPTC Guide Pipeline Crossings ............. 137

H

Hoop Stress ............................................... 66

Hot Tap Sizing .......................................... 13

I

IGT ............................................................ 49

ImpactLoad ............................................... 82

L

Live Load

AASHTO H20 Load on Buried PE Pipe -

Flexible or no Pavement

Aircraft Load on Buried PE Pipe .... 183

Local Atmospheric Pressure ..................... 35

M

MaxSpan ................................................... 97

Mueller - High Pressure ............................ 50

Mueller - Low Pressure ............................. 51

Multiple Vertical Anode in Parallel ........ 159

N

NiSource Blowdown Calculations .......... 142

O

Ohm's Law for Corrosion Current .......... 152

Orifice Meters ........................................... 12

Outlook Express .......................................... 6

P

Pack in Pipeline................................. 41, 145

Panhandle - A ............................................ 52

Panhandle - B ............................................ 53

Pipe Requirements for Horizontally Drilled

Installation............................................. 90

Pipe Wall Compressive Stress (PE Pipe

Crushing)............................................. 172

Pipeline Anchor Force Analysis ............... 84

Pipeline Purging - Gas Volume Lost ...... 143

Pipeline Rupture Analysis................... 43, 79

Pittsburgh .................................................. 54

Power Consumption of a Cathodic

Protection Rectifier ............................. 164

R

Rate of Electrical Current Flow Through the

Corrosion Cell ..................................... 149

Reciprocating Compressors - Capacity and

Horsepower ........................................... 30

Regulator Station Sizing ........................... 11

Reinforcement of Welded Branch

Connection ............................................ 20

Index

187

Relationship Between Resistance and

Resistivity ........................................... 150

Relief Valve Sizing ................................... 15

Relief Valves

Reaction Force ...................................... 19

Required Number of Anodes and Total

Current Requirement ........................... 161

Resistance to Earth of an Impressed Anode

Ground Bed ......................................... 156

Restrained Gas Pipeline - Stress Analysis 59

Rudenberg Formula ................................ 157

S

Soil Support Factor (Fs) .......................... 171

Spangler's Modified Iowa Formula ......... 167

Spitzglass .................................................. 55

T

Thrust at Blow-off................................... 104

Track Load Analysis ............................... 130

U

Unrestrained Gas Pipeline Stress Analysis -

Steel Pipe .............................................. 61

V

Values of E' for Pipe Embedment ........... 169

Values of E'n Native Soil Modules of Soil

Reaction .............................................. 170

W

Weymouth ................................................. 56

Wheel Load Analysis .............................. 123

Word ........................................................... 4