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SPECIFICATION FOR
PRESSURE VESSEL DESIGN
ESP-1101-1
Page 1 of 26
ESP-1101-1-R4-EN
ESP-1101-1
SPECIFICATION FOR
PRESSURE VESSEL DESIGN
4 31-may-05 MGG MGG JMV
3 may-02
2 mar-95
1 nov-94
0 ene-92
REV. DATE PREPARED BY APPROVED BYFINAL
APPROVALDESCRIPTION
SPECIFICATION FOR
PRESSURE VESSEL DESIGN
ESP-1101-1
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TABLE OF CONTENTS
1 GENERAL ISSUES..................................................................................................................5
1.1 Purpose............................................................................................................................5
1.2 Scope ...............................................................................................................................5
1.3 Applicable codes, regulations and standards...............................................................5
1.3.1 Spanish Regulations and Standards ..........................................................................5
1.3.2 Sections of the ASME Boiler and Pressure Vessels Code..........................................5
1.3.3 ASME / ANSI Code ....................................................................................................6
1.3.4 EEC standards...........................................................................................................6
1.3.5 Other Standards and Codes indicated on the Drawings or Data Sheets.....................6
2 DEFINITIONS ..........................................................................................................................6
2.1 Design pressure ..............................................................................................................6
2.2 Design temperature.........................................................................................................8
2.3 Actions to consider.........................................................................................................8
2.3.1 General ......................................................................................................................8
2.3.2 Loads due to piping thrust ..........................................................................................9
2.3.3 Weights of the connected piping ................................................................................9
2.3.4 Loads due to wind ......................................................................................................9
2.3.5 Loads due to earthquakes........................................................................................10
3 DESIGN CRITERIA................................................................................................................11
3.1 Allowable stresses........................................................................................................11
3.1.1 Allowable tensile stresses ........................................................................................11
3.1.2 Allowable compressive stresses...............................................................................11
3.1.3 Allowable shear stresses..........................................................................................11
3.1.4 Other allowable stresses for horizontal vessels ........................................................12
3.2 Required thickness .......................................................................................................12
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3.3 Corrosion allowance.....................................................................................................13
3.4 Heads and transition sections......................................................................................14
3.5 Supports ........................................................................................................................15
3.6 Davits .............................................................................................................................16
3.7 Nozzles, manholes and inspection holes ....................................................................16
3.7.1 General ....................................................................................................................16
3.7.2 Rating ......................................................................................................................16
3.7.3 Dimensional characteristics......................................................................................17
3.7.4 Types of Flanges......................................................................................................17
3.7.5 Types of faces..........................................................................................................17
3.7.6 Stresses transmitted through the pipes ....................................................................18
3.7.7 Manholes and inspection holes ................................................................................18
3.7.8 Miscellaneous ..........................................................................................................19
4 TESTING AND ANALYSIS ....................................................................................................19
4.1 Hydraulic tests ..............................................................................................................19
4.1.1 General ....................................................................................................................19
4.1.2 Test pressure. ..........................................................................................................19
4.1.3 Test temperature......................................................................................................20
4.2 Vibration analysis .........................................................................................................21
5 MATERIALS ..........................................................................................................................21
5.1 General...........................................................................................................................21
5.2 Plates .............................................................................................................................22
5.3 Pipes ..............................................................................................................................22
5.4 Flanges ..........................................................................................................................23
5.5 Gaskets, bolts and nuts................................................................................................23
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1 GENERAL ISSUES
1.1 Purpose
The purpose of this specification is to define the minimum requirements in design of Pressure
Vessels, with welded construction, not subjected to fire and built from carbon steel, alloy steel,
stainless steel or coated with another metallic material.
Attached to this specification as a part of the same, drawings or Data Sheet will be published
indicating the specific characteristics of each vessel.
The purpose of this specification is not to replace the applicable codes and standards but only to
supplement certain details.
1.2 Scope
This specification applies to all projects to be undertaken within the scope of GRUPO CEPSA
COMPANIES, under any of the possible systems of procurement.
1.3 Applicable codes, regulations and standards
The design and selection of materials will be according to the latest issues of the following Codes,
Regulations and Standards. It must also comply with the requirements of the applicable national
legislation.
1.3.1 Spanish Regulations and Standards
- Royal Decree 769/1999 of May 7, by which the implementing rules of the Directive of the
European Parliament and Council 97/23/EC are dictated, concerning pressure equipment and
amending the Royal Decree1244/1979 of April, which the Pressure Equipment Regulation
approved.
- General Ordinance for Workplace Health and Safety.
- Basic Building Standard NBE-AE-88, Actions in Building.
- Earthquake-Resistant Standard NCSE-94.
- Royal Decree 2085/1994 by which the Regulation of oil facilities is approved.
1.3.2 Sections of the ASME Boiler and Pressure Vessels Code
- Section II Material Specifications.
- Section VIII, Division 1. Rules for Construction of Pressure Vessels.
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- Section II Non-destructive Examination.
- Section IX Welding qualification.
1.3.3 ASME / ANSI Code
- ASCE-7 Minimum Design Loads.
- B1.1 Unified Inch Screw Threads.
- B2.1 Pipe Threads.
- B16.5 Pipe Flanges and Flanged Fittings.
- B16.11 Forged fittings socked welded and Threaded
- B16.20 Metallic Gaskets for Pipe Flanges.
- B31.3 ASME Code for Pressure Piping. Process Piping.
- B36.10 Welded and Seamless Wrought Steel Pipe.
- B36.19 Stainless Steel Pipe.
- B46.1 Surface Texture.
- B16.47 Large Diameter Steel Flanges.
1.3.4 EEC standards
DIRECTIVE 97/23/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 29 May
1997 on the approximation of the laws of the Member States concerning pressure equipment.
1.3.5 Other Standards and Codes indicated on the Drawings or Data Sheets
In case there is any inconsistency between the above mentioned Rules and Regulations and the
requirements of this specification, it should be brought to the attention of CEPSA, which reserves
the right to decide in each case as appropriate.
2 DEFINITIONS
2.1 Design pressure
Design gauge pressure, measured in the highest part of the vessel in service position, will be that
given in the Basic Engineering and reflected in the drawing or Data Sheet of the vessel.
When this figure does not appear in Basic Engineering, the design pressure shall be deemed to be
the highest of the following values:
- 110% of the maximum operating pressure.
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- Maximum operating pressure increased by 2 kg/cm2
- 3.5 kg/cm2 (m).
When the maximum operating pressure is not known, the design pressure shall be that indicated in
the following table:
Normal operating pressure (m) Design pressure (m)
0 - 1.5 kg/cm2 3.5 kg/cm2
1.6 kg/cm2 - 13.5 kg/cm2 2 kg/cm2 + P.O.
13.6 kg/cm2 - 20 kg/cm2 115% of P.O.
20.1 kg/cm2 - 25 kg/cm2 2 kg/cm2 + P.O.
25.1 kg/cm2 and over. 112% of P.O.
With P.O. being: Normal operating pressure.
Only those pressure vessels that are actually subjected to vacuum during operation (including
start-up and shutdown) will be also designed for vacuum.
Whichever the degree of vacuum is, these vessels will be designed for full vacuum (1.05 kg/cm2 of
external pressure), and the temperature indicated, in addition to the considerations given in
paragraph 2.1. regarding positive pressure.
Vessels not subjected to vacuum, in which this situation may occur due to improper operation,
failure of any control etc. shall be designed with a vacuum breaker system.
For vessels with double shell, the external pressure for the inner shell will be deemed to be the
internal pressure marked for the outer shell. If the recipient is subjected to vacuum, the expected
external pressure will be increased to 1.05 kg/cm2.
For vessels consisting of several contiguous and completely independent chambers, each
chamber will be designed at its internal design pressure and external pressure, taking into account
the maximum concurrent differential pressure.
If any or all of the chambers are subjected to vacuum, this vacuum will be added to the maximum
concurrent differential pressure.
If due to process conditions there is a possibility that any of the chambers could be depressurised,
this chamber or chambers will be designed to an external pressure equal to the pressure inside the
adjoining chamber with the highest internal pressure.
For vessels subject only to internal pressure, the maximum external pressure shall be calculated
so that the vessel can withstand at 150ºC, assuming that the expected corrosion allowance is
completely exhausted.
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This maximum allowable external pressure will be reflected in the Drawings or Data Sheet of the
vessel.
When it is specified a pressure drop produced by any internal element within the vessel, this
pressure drop along with the pressure due to the fluid column existing in the head of the vessel,
will be taken into account in determining the design pressure of the corresponding element.
In vertical vessels, it shall be deemed that the column of liquid reaches the first plate counting from
the floor.
In horizontal vessels, it shall be deemed that the vessel is completely filled with fluid.
2.2 Design temperature
The design temperature shall be that given in the Basic Engineering and reflected in the Drawings
or Data Sheet of the vessel.
When this figure does not appear in Basic Engineering, the design pressure shall be deemed as
the maximum operating temperature plus 15ºC.
Excluding vessels with interior thermal lining, the temperature of the metal shall be deemed as the
same as the fluid temperature within the vessel.
For vessels with interior thermal lining, the design temperature of the metal shall be determined by
calculation, using the internal temperature as the maximum operating temperature. The external
temperature shall be deemed as the maximum room temperature but not exceeding 45ºC.
When it is possible to establish perfectly divided zones operating at different temperatures in a
vessel, each zone needs to be designed based on its respective design temperature.
Vessels operating at temperatures below 20ºC will be designed at a temperature equal to the
minimum operating temperature.
If for operational reasons it becomes necessary to vaporise a vessel, the maximum steam
temperature shall be recorded in the Drawings or Data Sheet of the vessel, provided that this
temperature exceeds the design temperature.
2.3 Actions to consider
2.3.1 General
Loads to be considered in the design of a vessel shall be as specified in paragraph UG-22 of the
ASME Code, Section VIII, Division 1, taking from these, those that exist for the following
conditions: installation, start-up, operation or hydraulic testing.
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2.3.2 Loads due to piping thrust
For this calculation, we will assume an horizontal force acting on the upper nip. Its value in kg is
the product of multiplying 25 by the nominal diameter of the largest diameter nozzle existing in the
vessel (excluding manholes).
2.3.3 Weights of the connected piping
To take into account the weights of the connected pipes, the weight of the vessel shall be
increased to:
- 5% if the relationshipD
Lis lower than 10.
- 3% if the relationshipD
Lis greater than or equal to 10.
In which:
L = height of the vessel (including skirt).
D = average diameter of the vessel.
2.3.4 Loads due to wind
Loads due to wind action shall be calculated according to the NBE-AE-88 Standard “Actions in
Building”, considering that the topographical situation is exposed to the wind.
The design pressure shall be obtained using the following formula:
P = p . c . k . m
P = design pressure.
p = dynamic wind pressure (Table 5.1 of NBE-AE-88).
c = wind coefficient (Table 5.3 of NBE-AE-88).
k = wind slenderness factor (Table 5.5 of NBE-AE-88) (*)
m = coefficient of pipes, platforms and ladders according to the following table:
Outer diameter (mm)
(Including insulation)Coefficient (m)
D 500 1.50
500 < D 1,000 1.40
1,000 < D 1,500 1.30
1,500 < D 2,000 1.25
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2,000 < D 2,500 1.20
2,500 < D 1.15
(*) In the case of vessels with transition sections, the value of “b” used in Table 5.5 shall be that of
an equivalent diameter calculated using the following formula:
D1 L1 + D2 L2 + D3 L3 + …..
b = -------------------------------------------
L1 + L2 + L3 + …..
In which:
L1, L2, L3, …., the lengths of the different zones
D1, D2, D3, …., the respective outer diameters.
For tapered areas, we shall use their average diameter.
2.3.5 Loads due to earthquakes
Seismic loads are calculated according to the ASCE-7 Standard.
Appendix A summarises the calculation method according to the cited Standard.
When seismic loads, calculated in accordance with the preceding paragraph, are determining
factors in determining the thickness of the various elements of the vessel, those calculations
referring to seismic actions shall be in accordance with the requirements of the NCSE-94
Earthquake Resistance Standard.
The fundamental period of vibration shall be calculated using a method that takes into account the
stiffness and mass distribution along the height of the vessel.
Appendix B summarises the methods proposed by FREESE (for standard vessels) and WARREN
W. MITCHELL (for irregular vessels).
For vessels not placed in a highly exposed topographical situation, it shall be considered during
installation, start-up and operation that all applicable loads are acting simultaneously, including
those for wind and earthquakes. Of these last two, only the larger shall be considered.
For vessels placed in a highly exposed topographical situation, with the rest of the loads
applicable, for the purposes of wind and earthquake, the larger of the two following circumstances
shall be considered:
The maximum wind load.
The seismic actions acting concurrently with the wind action, the latter affected by a
reduction coefficient of 0.25.
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During hydraulic tests in the field, it shall be considered that along with the loads in the test itself,
the wind loads specified in paragraph 2.3.4 shall act, affected by a reduction coefficient of 0.25.
3 DESIGN CRITERIA
3.1 Allowable stresses
3.1.1 Allowable tensile stresses
3.1.1.1 Elements under pressure
The maximum tensile stress to which these elements may be subjected shall not exceed the
maximum allowable stress that is specified for the design temperature in paragraph UG-23.a of
the ASME Code, Section VIII, Division 1, for the selected material and affected by the welding
efficiency coefficient.
3.1.1.2 Elements not subject to pressure
The maximum tensile stress to which these elements may be subjected shall not exceed the
maximum allowable stress that is specified for the design temperature in paragraph 302.2 of the
ASME/ANSI Code B 31.3, for the selected material and affected by the welding efficiency
coefficient.
3.1.2 Allowable compressive stresses
The maximum compressive stress to which any element of the vessel may be submitted, whether it
is subjected to pressure or not, shall be the smaller of the following two values:
Its allowable tensile stress (welding coefficient E = 1).
That is determined using the procedure given in paragraph UG-23.b (2) of the ASME Code,
Section VIII, Division 1.
3.1.3 Allowable shear stresses
The maximum shear stress to which any element of the vessel may be submitted shall not exceed
80% of the maximum allowable tensile stress of the material based on its design temperature
(welding coefficient E = 1).
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3.1.4 Other allowable stresses for horizontal vessels
The additional stresses that occur in the heads when they are located at a distance from the
saddles of less than 0.5 times the radius of the vessel, combined with the hoop stress due to
pressure, must be less than 125% of the allowable tensile stress affected by the welding efficiency
coefficient.
The circumferential stresses at the ends of the saddles shall not exceed 125% of the allowable
tensile stress (welding coefficient E = 1).
The compressive stresses due to the reactions of the saddles shall not exceed half the yield
strength of the material at the design temperature.
When loads due to wind or earthquake are combined with the other loads applicable, the values of
the allowable stresses, both tensile and compressive for the pressure elements, may be increased
by 20%, when the provided design temperature does not exceed the values shown in Table UG-
23.1 of the ASME Code, Section VIII, Division 1.
During the hydraulic tests, the maximum allowable tensile stress shall not exceed 90% of the yield
strength of the selected material, affected by the efficiency coefficient of the welding efficiency
coefficient.
During the hydraulic tests, the maximum compressive stress may not exceed the values given in
3.1.2. at room temperature.
The allowable stress for the anchor bolts shall not exceed 1,200 kg/cm2.
3.2 Required thickness
When calculating the required thickness of pressure vessels and their supports, in addition to the
requirements of ASME Code, Section VIII, Division 1, the following additional criteria shall be taken
into account:
The minimum thickness, excluding the corrosion allowance of the shells and heads of the
pressure vessels shall not be lesser than any of the following values:
- D/1,000 + 2.5 mm, where D = internal diameter of the vessel.
- 5 mm for carbon steel or low-alloy vessels.
- 3 mm for vessels of medium and high alloy, including any kinds of stainless steel.
In horizontal vessels supported on saddles, lateral deformations (buckling) must be prevented.
Local stresses due to bending and shear stress must not exceed the allowable set out in
paragraph 3.1.4.
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The ZICK LP method (see Pressure Vessels and Piping: Design and Analysis. Volume II
ASME), can be used for this study.
Vessels should be designed to be tested with water in their operating position, without their
stresses exceeding at any time the allowable limits referred to in paragraphs 3.1.6. and 3.1.7.
The maximum deflection permissible in vertical vessels, calculated by taking into account all
the combined stresses except the seismic, shall not exceed 4.5 mm on each side of the axis for
each metre of height.
3.3 Corrosion allowance
The normal corrosion allowance will be indicated on the Drawings or Data Sheet of the vessel
according to the following table:
Vessel materialNormal
corrosion allowance (mm)Carbon steels 3 (1)
Low alloy steels 3 (2)
Medium alloy steels 1.5 (3)
High alloy and stainless steels 1.5 (4)
Non-ferrous materials 0.5
Vessels with lining 0 (5)
NOTES: (It is permissible to consider 1/8” = 3 mm)
(1) Includes any type of carbon steel, including steels with carbon manganese and microalloyed
carbon steels.
(2) Includes alloy steels:
1/2% Cr - 1/2% Mo 2¼ % Cr - 1% Mo
1% Cr - 1/2% Mo 5% Cr - 1/2% Mo
1¼% Cr - 1/2% Mo
(3) Includes alloy steel 9% Cr - 1% Mo
(4) Includes alloy steels with more than 9% Cr, including any stainless steels.
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(5) It refers to coatings, both metallic and non-metallic, resistant to corrosive environments under
normal conditions of operation, provided that contact of fluid with the covering material is
completely prevented.
The corrosion allowance shall be added to all surfaces of elements in contact with the fluid
according to the following criteria:
a) All elements subjected to pressure.
b) All elements welded to the inside part of the vessel and on each of the surfaces in contact with
the fluid being held in the vessel.
c) In vessels of two or more shells , on each of the surfaces of the intermediate heads.
d) To all internals which are screwed-in and detachable, except for the detachable plates on the
columns, will be added half of the corrosion allowance specified for each of the surfaces in
contact with the fluid being held in the vessel.
When to resist corrosion the vessel is equipped with an interior metallic lining of a “CLADDING”
type, the minimum thickness of this coating shall be 3 mm. This coating will only be considered as
protection against corrosion and only the base metal shall be considered for the purposes of
supporting stresses.
If the rate of entry of the product in the vessel is greater than 10 m/sec, or if accelerated corrosion
is expected in the catchment area of the liquid flow, a wear plate must be installed with 10 mm
minimum thickness, made of the same material as the shell that completely covers this area.
Additional corrosion allowance will be added of not less than 1.5 mm to the supports, such as
skirts, saddles, consoles and legs, as well as the base ring.
Additional corrosion allowance shall be added of 3 mm to the diameter of the anchor bolts. In no
case shall it be less than 25 mm.
3.4 Heads and transition sections
Normally the pressure vessels heads shall be torispherical Klopper type. Torispherical bases
Korbbogen type, elliptical with a maximum ratio of 2:1 or hemispherical, shall be used when any of
the following conditions arise:
a) Design pressure greater than or equal to 7 kg/cm2.
b) Design temperature greater than 350ºC.
c) Vertical vessels lower Heads whose relationship:
D
Lis greater than or equal to 10.
L = Height of vessel (including skirt) - D = Mean diameter of the vessel).
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d) Upper heads of vertical vessels which need to support concentrated loads (mixers etc.).
Conical type Heads and transition sections will be toriconical with knuckle areas
The internal agreement radius shall never be less than 6% of the outside diameter of the adjacent
cylindrical section, except when the wall thickness of the knucke area is equal to or greater than 20
mm, in which case it shall not be less than 10% of the outside diameter quoted above.
The vessel heads over which agitators are mounted shall be designed with adequate stiffness, in
order to minimise the deformations due to static and dynamic loads transmitted by them.
Stresses in the Knuckle area of the torispherical heads that have a thickness/diameter ratio of less
than 0.002 shall be calculated so as to ensure stability against buckling.
Heads with a diameter equal to or less than 3,400 mm shall be made in one single piece.
Intermediate heads shall be connected to the shell according with figure UW 13.1 (f) of ASME
Code, Section VIII, Division 1, angled welded joint.
3.5 Supports
The vertical vessels shall be designed as self-supported units. The following can be used as
supports: skirts, legs, saddles and consoles.
Skirts shall be used when any of the following conditions are fulfilled:
a) The diameter of the shell is greater than 1,500 mm.
b) The vessel total height / diameter ratio is greater than 5, or if the height of the support is
greater than 1,500 mm.
c) Vibrations can be expected.
d) The weight of the vessel when filled with water is greater than 15,000 kg.
The skirt and anchor bolts shall be designed for the least favourable load condition, including the
hydraulic test.
The skirts shall be welded to the lower head so that the average diameters of the skirt and shell
match. In no event shall the skirt be welded to the outside of the shell.
Flanged or threaded joints are not permitted on the inside of the skirt Nozzles of vessel’s lower
head will have a 90° elbow and a horizontal extension pipe to the outside of the skirt, ending in a
flange.
All skirts shall have at least one access opening in accordance with Standard STD-RP-033 and
shall be fitted with a removable grid in accordance with Standard STD-RP-043.
- For vessel diameter of 2,500 mm: 1 opening.
- For diameters above 2500 mm: 2 openings.
4 inches diameter vent nipples shall be placed at the top of the skirt, to vent the space below its
intersection with the lower head.
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The number of vents, equally spaced, will be:
- Vessel diameter > 1,000 mm 4 vents.
- Vessel diameter 1,000 mm: 2 vents.
Pipe sleeves will be used for each and every one of the pipes passing through the skirt. These
pipe sleeves will be large enough to allow for heat insulation and thermal expansion.
The inner and outer projection of the reinforcements of skirt openings, vents and pipe sleeves for
the passage of pipe shall be a minimum of 50 mm and 15 mm respectively greater than the
thickness of the fireproofing.
Horizontal vessels shall be designed to be supported by two saddles that will be made of carbon
steel and will cover at least 120° of the circumference of the vessel.
The saddles will be attached to the vessel through reinforcing plates of the same thickness as the
shell, and will have dimensions in accordance with Standards STD-004 and RP 006.
3.6 Davits
All columns or reactors will have a davit installed with sufficient capacity to dismount the overhead
valves and/or internals. In no case shall its capacity be less than 500 kg. This davit will be in
accordance with the Standard STD-RP-044.
3.7 Nozzles, manholes and inspection holes
3.7.1 General
All connections shall be flanged. The connections of three-inch nominal diameter and larger must
be provided with a reinforcing plate whose minimum dimensions are those indicated in the
Standard STD-RP-026.
Connections with a rating above 600 # shall be self-reinforcing.
The connections will be a minimum of 1½” in diameter
3.7.2 Rating
The rating of the flanges will be appropriate for the conditions of design pressure and temperature
of the vessel in accordance with ASME/ANSI B 16.5 Standards (Steel Pipe Flanges and Flanged
Fitting).
For design temperatures above 350ºC or safety valve connections, it is not permitted to use
flanges with a rating of 150 #. Instead, flanges shall be used with a rating of 300 # or more.
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3.7.3 Dimensional characteristics
Flanges with a nominal diameter of 24 inches and below shall comply with ASME/ANSI
Standard B 16.5 for all materials and ratings
Flanges with nominal diameters greater than 24 inches and a rating not exceeding 300 # shall
comply with ASME B.16.47 “Large Diameter Steel Flanges” Series B.
For sizes larger than 24 inches nominal diameter of, in carbon steel vessels with rating above 300
# and steel or stainless steel alloy vessels with any rating, flanges shall be designed and
calculated in accordance with the ASME Code, Section VIII Division 1, Appendix 2.
Internal flange connections not subject to pressure will be in accordance with Standard STD-RP-
025.
3.7.4 Types of Flanges
All flanged connection of 3 inches and larger, including manholes and inspection holes, will be of
Welding Neck type.
flanges with sizes of 1½ and 2 inch shall be of the Long Welding Neck type
The only exception is that “SLIP-ON” type flanges may be used in carbon steel vessels with no
internal metallic lining, if the following conditions occur simultaneously:
- Nominal diameters greater than or equal to 16 inches.
- Required rating of 150 #.
- Design temperature no higher than 230ºC.
- Expected corrosion or erosion of less than 0.15 mm/year.
- No posterior thermal treatment is required for the welding.
- Cyclical variations in temperature are not expected, as defined in the ASME/ANSI B 31.3
Code.
- They do not operate for service of: Hydrogen, Wet SH2, Amines, Caustic Soda and
Hydrofluoric acid.
thickness of the connection pipes shall be in accordance with the Standard STD-RP-028.
The Sch. of pipes and WN flanges of the connections shall coincide.
The Sch. of the base connections of columns whose total height/diameter relationship is greater
than 10 shall be that immediately above the one indicated in Standard STD-RP-028.
3.7.5 Types of faces
Faces of the flanges shall be those specified in the Data Sheets, needing to be RTJ from 2,500 LB
in accordance with ANSI B16.20.
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Surface finish of the flange faces shall be smooth or fine matte, with a roughness between 125 and
250 Ra, in accordance with ASME/ANSI B46.1.
3.7.6 Stresses transmitted through the pipes
Connections should be designed to withstand, as a minimum and without exceeding the allowable
stresses for materials used in the course and connection, those forces and situations indicated in
Standard STD-RP-050.
3.7.7 Manholes and inspection holes
Vessels of internal diameter equal to or less than one meter with replaceable internal parts shall
have one flanged bottom and shall be fitted with lugs for lifting. In addition, they shall also have a
manhole of at least 6 inches at the other end.
Vessels of internal diameter equal to or less than one meter without replaceable internal parts shall
have the number of manholes necessary for the inspection of all the representative unions of the
course and critical elements. Their size cannot be less than 6 inches.
flange connections for instrumentation or pipes with diameters greater than or equal to 6 inches
can be considered as manholes
Horizontal vessels shall have a manhole in one of the heads and/or in the course. The vents shall
preferably be positioned at the opposite end of the manholes
The manholes of the columns shall be located as follows:
- Above the overhead tray
- Above the normal feed tray
- Above the extraction tray
- Below the lower tray.
The maximum distance between the manholes on the columns containing trays shall not exceed
6 metres.
The manholes shall have a minimum diameter of 24 inches.
For special services such as loading and emptying of catalysts, handling of trays and large
removable internal parts etc., the diameter of the manholes shall be consistent with their intended
use.
All blind flanges of manholes and other flanges whose weight exceeds 40 kg shall be equipped
with davits or hinges, in accordance with Standards STD-RP-017, 018, 019 or 020.
The manholes shall be placed so as to avoid the personal risks that might occur when team staff
enter or leave, due to: internal parts, drains and other openings.
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To facilitate this operation, there shall be handles, in accordance with Standard STD-RP-029.
3.7.8 Miscellaneous
The minimum projection of flange connections from the outer surface of the course shall be that
indicated in the Standard STD-RP-035.
When vessels are thermally insulated, the projections shall increase in the lagging thickness
indicated in ESP-4205-1 and Drawing or Data Sheet of the vessel.
The connections of nominal diameter of three inches and above must be provided with a
reinforcing plate whose minimum dimensions are those indicated in Standard STD-RP-026.
Connections with nominal diameters less than three inches with projections above those required
in the preceding paragraph shall be provided with stiffeners.
Nozzles and reinforcements cannot be located:
a) In the region of the knuckle area of torispherical heads.
b) In the region of the transition section between a cylindrical course and a conical course.
Tightening of the bolts in all the nozzles, including manholes, shall be performed in accordance
with the specification ESP-0200-2.
4 TESTING AND ANALYSIS
4.1 Hydraulic tests
4.1.1 General
All vessels shall be designed to withstand the following hydraulic tests:
a) Manufacturer's workshop test shall be performed with the vessel in its manufacturing
position, if it is not possible in its operating position. It shall be in accordance with ASME VIII,
Div. 1, and Directive 97/23/EC (the highest of those calculated).
b) Initial test at the installation site shall be performed with the vessel in its operating position,
in accordance with ASME VIII, Div. 1, and Directive 97/23/EC.
Periodic tests shall be performed in accordance with RAP-MIE-AP6.
Ph = 1.25 * Pd *d
h
S
S
4.1.2 Test pressure.
Values of the hydraulic pressure test of paragraph 4.1 are as follows:
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Ph = 1.3 * Pd *d
h
S
S(S/ASME VIII, Div. 1)
Ph = 1.43 * Pd or 1.25 * Pd *d
h
S
S(as per Directive 97/23/EC)
In which:
Ph = Test pressure.
Pd = Design pressure.
Sh = Allowable stress of the material at the test temperature.
Sh = Allowable stress of the material at the design temperature.
The following limitation should be taken into account:
Sh
------ : For this ratio, shall be taken from the section which gives a value which is
Sd Lower in cases in which the vessel can distinguish different sections due to different
design temperatures or different materials.
The value of the hydraulic test pressure of vertical vessels which are tested in a horizontal position
will be that obtained applying the above formula by increasing the water column pressure
corresponding to the height of the vessel.
In case that due to the value of the hydraulic test pressure as determined above it becomes
necessary to modify the flanges of the vessel, the hydraulic test value shall be taken to be the
maximum value that allows the limiting element without modification.
When testing austenitic stainless steel components, water with more than 30 ppm chloride may not
be used. The equipment shall be drained and dried immediately after the test via use of air stream.
4.1.3 Test temperature
When the thickness of the vessel is greater than 13 mm, the metal temperature of the vessel
during the hydraulic test shall be as follows:
a) For thicknesses of 50 mm or lower, the temperature shall be at least 6°C above that from
which impact testing is required in accordance with ASME, Section VIII, Division 1.
b) For thicknesses over 50 mm, the temperature shall be at least 17°C above that from which
impact testing is required in accordance with ASME, Section VIII, Division 1.
c) When, in accordance with the requirements of the previous two sections, a vessel
temperature during the test pressure greater than 21ºC is required, the minimum
temperature at which the vessel must be maintained shall be marked on its nameplate.
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d) The minimum test temperature shall be determined by the manufacturer and shall be
included on the drawings, nameplate and the Technical Sheet of the equipment.
4.2 Vibration analysis
A vibration analysis shall be performed provided that the following conditions occur simultaneously:
a) Total column height exceeds 30 metres.
b) W----------- 25
L Dr2
In which:
L = Total column height, in feet.
W = Total weight of the column, including internal parts, in pounds.
Dr = Average diameter of the upper half of the column, in feet.
In the case of the equipment including dynamic internal parts, there shall be special
considerations.
5 MATERIALS
5.1 General
The materials used in the construction of the vessels subjected to pressure shall be indicated on
the drawings or Data Sheets of the vessel and shall be in accordance with ASME Code, Section II
and with the limitations set forth in the following paragraphs.
The maximum carbon content or carbon equivalent of the steel to be welded shall in no case be
higher than the values in the table below:
Vessel material % C. (3) % Ceq.
Carbon steels (1) 0.25 0,41 (4)
Microalloyed carbon steels. 0.20 0,42 (5)
Chromium-molybdenum steels (2) 0.15 -
NOTES:
(1) Includes any type of carbon steel, including carbon manganese steels.
(2) Includes medium and low alloy steels (9% Cr and under).
(3) Only applicable when the material composition indicates values greater than these.
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(4) Determined by the formula:
% Mn
% Ceq = % C + -----------
6
(5) Determined by the formula:
% Mn % Cr + % Mo + % v % Ni + % Cu
% Ceq = % C + ---------- + ------------------------------- + ---------------------
6 5 15
Any non-pressure part welded to a pressure part shall be of the same quality as the latter. To this
end, the conditions of killed and microalloyed carbon steels, must be understood as different
qualities to simple carbon steel.
5.2 Plates
The quality of the sheets for courses and heads of the vessels shall be:
When carbon steel is indicated, the minimum acceptable quality shall be in accordance with the
specification SA 285 Gr.C.
When killed carbon steel is indicated, the minimum materials shall be in accordance with the
specification SA-516 (preferably Gr. 60).
When medium or low alloy steel or stainless steel is indicated, the materials shall be in accordance
with specifications SA-387 or SA-240 respectively.
The sheets for vessels with metal lining shall be in accordance with the specifications SA-263, SA-
264 or SA-265.
The upper half metre of the skirt shall be made of the same material as the vessel. The rest of the
skirt shall be in accordance with the specification SA-285 Gr.C.
The steel sheets of the base shells, reinforcement of the openings of the skirt and saddles are
horizontal vessels according to the specification SA-285 Gr.C.
All internal parts welded to the courses or headswill be made of the same type of material as the
inner surface of the vessel.
The structural elements that are not welded directly to the courses or heads of vessels shall be in
accordance with specification SA-285 Gr.C.
5.3 Pipes
Pipes used for nozzles, with nominal diameters up to 16 inches inclusive, shall be seamless and in
accordance with the following specifications:
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For carbon steel and killed carbon steel vessels: SA-106, Grade B.
For steel vessels of medium or low alloy: SA-335 and grade of the course material.
For ferritic stainless steel vessels: SA-268 and grade of the course material.
For austenitic stainless steel vessels: SA-312 and grade of the course material.
Nozzles of nominal diameters over 16 inches can be manufactured with the same quality sheet-
metal as the courses and with the thicknesses given in the Standard STD-RP-028.
5.4 Flanges
The materials used in the manufacture of flanges shall be in accordance with the following
specifications:
a) For carbon steel and killed carbon steel vessels. SA-105.
b) For alloy or stainless steel vessels: SA-182 and the grade corresponding to the course
material.
5.5 Gaskets, bolts and nuts
These shall be those corresponding to the class of pipe.
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ANNEX A. LOADS DUE TO EARTHQUAKES.
A-1. Vessels shall be designed taking into account that the effect of the earthquake is a lateral
static load whose value is given by:
V = Z . I . K . C . S . W
In which:
Z = seismic factor.
This is a function of the seismic zone where the vessel is located. Its value is given by:
Seismic Zone Value of Z
First 0.1875
Second 0.3750
Third 0.7500
Seismic zones shall be determined according to the NCSE-94 Standard on Seismic Resistance.
I = Load factor.
This depends on the intended use of the vessel. I = 1 will always be used.
K = Structure coefficient.
This is a function of the inherent resistance of the type of structure to the dynamic forces due to an
earthquake. For vessels, K = 2 will be used.
C = Flexibility factor.
Its value is given by the expression: C =T15
1
Where T = fundamental period of vibration in seconds.
C shall be limited by: 0,04 < C 0,12
S . Soil and foundation factor.
S = 1.5 will be used, which will be limited by: C . S 0.14
W = Weight of vessel including the skirt.
A-2. Distribution of lateral load
The total lateral load V will be distributed along the height of the vessel in accordance with the
expression:
x = n
V = Ft + Fx
x = 1
In which:
Ft = Concentrated force applied at the crest of the vessel and whose value is given by:
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Ft = 0.07 T.V. 0.25 V
For T 0.7 seconds, Ft = 0
The rest of the total lateral load V will be distributed along the height of the vessel including the
higher value “n” in accordance with the expression:
(V – Ft) Wx hx
Fx = -----------------------
Wx hx
In which:
Fx = Lateral load acting at the centre of gravity of the element considered.
hx = Height from base to the centre of gravity of the element considered.
Wx = Own weight in operation of the element considered.
A-3. Bending moments
The existing bending moment at the bottom of each section shall be calculated using the
expression:
Mx = Ft (H - hi) + Fx (hx - hi)
In which:
H = Total height of vessel including the skirt.
hi = Height from base to the lower level of the element considered.
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ANNEX B. CALCULATION OF THE FUNDAMENTAL PERIOD OF VIBRATION
B.1. For uniform vessels
Uniform vessels are understood to be those whose diameter, thickness, weight and temperature is
constant along the entire height of the vessel.
For this type of vessel, the FREESE formula shall be used, which is given below:
T = 2 x 10-4
2
Do
H
)(
.
ctH
DoW
H = Total height of vessel including the skirt. In millimetres.
Do = Outside diameter of the vessel. In millimetres.
W = Total weight of the vessel in operation. In kg.
t = Total wall thickness. In millimetres.
c = Corrosion allowance In millimetres.
B-2. For non-uniform or irregular vessels
These are understood to be those vessels in which at least one of the variables mentioned in the
previous section varies.
For such vessels, the calculation of the fundamental period of vibration shall be carried out
according to the method proposed by WARREN W. MITCHELL, given below:
Wx + Wz / H
T = 1,97 x 10-4 H2 -------------------------------------
Ex Dox3 (tx - c)
H = Total height, including the skirt. In millimetres.
Wx = Uniform unit weight of each section. In kg/metre.
Dox = Outside diameter of each section. In millimetres.
tx = Thickness of each section. In millimetres.
Ex = Module of elasticity of each section by 10-6. In kg/cm2.
Wz = Significant concentrated fixed loads. In kg.
c = Corrosion allowance. In millimetres.
hx = Height of centre of gravity of each section. In millimetres.
= Coefficient of influence of the different sections. (See table).
= Coefficient of influence of concentrated loads. (See table).
= Coefficient of influence of the stiffness of each section. (See table).
