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SIMPLEST PIPING DESIGN (1/5)

RJ-Arabian

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Contents

Process Piping Design

Pipe Size Concept & Calculation

RJ-Arabian

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Process Design

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Process Piping Design Involves to Calculate;

Flow Rates Fluid Velocities Pressure Drops Reynolds Numbers Friction Factors Fitting Losses Component Losses Node Pressures Pump Operating Points Pump Head Added Pump Inlet Pressure NPSHa at Pump Inlet Hydraulic Grade Lines Energy Usage Breakdown

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Mechanical Design

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Mechanical Piping Design Involves;

Pipe Materials Selection Pipe Wall Thickness Stress Analysis

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Process Design in Detail

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Why Process Design? (It makes the START of piping design)

What Process Design ? (At least calculations of Line Sizes or pipe

internal diameter)

How Process ?? (Need to know or calculate at least Flow Rates, Fluid

Velocities, Pressure Drops)

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Calculation

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Steps-1 (Fluid Information):

Fluid Parameters example

Fluid Type Water

Temperature at 30 oC

Pressure and 1 bar Pressure

Flow rate with a Flow rate of 0.01 m3/sec

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Calculation

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Step-2 (Selection of Velocity)

You have to select an approximate velocity

There are firm rules for selection as many factors involve in final

selection, however

You can find some literature for just a starting point (shown in next slides)

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example

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Fluid Velocity

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Fluid Velocity

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Calculation

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Step-3 (Flow Area Calculation)

Area = Volume Flow Rate

Velocity

m2 = m3 x sec = m2

sec m

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Calculation

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example

Fluid = Water

Flow Rate = 0.01 m3/sec

Velocity = 2 m/sec

Area = Volume Flow Rate = 0.01 = 0.005 m2 = 5000 mm2

Velocity 2

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Calculation

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Outer Diameter

AREA = /4 * (d)2

5000 = 3.14/4* (d)2

Inner Diameter

Step-4 (Pipe Internal Diameter)

d = 80 mm

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Calculation

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Step-5 (Checking with Standards)

The diameter you calculated is not necessarily available in the market.

Now check which internal diameter pipe is available in market that is

close to your calculated 80 mm pipe

Check a market standards document called ASME-B-36.10

Two pages of this standard are copied here, you only need to check

outer diameter of pipe and then subtract the wall thickness 2 times to

get internal diameter

Always select a diameter slightly higher then you calculate not less.

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Pipe Standards

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Outside Diameter = 101.6 mm

Wall Thickness = 5.74 mm

Inside Diameter of Pipe = 101.6 2(5.74) = 90.12 mm

Note that we select STD it means this is a Standard thickness pipe which is OK for most of the cases.

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Pipe Diameter

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Outer Diameter

101.6

Inner Diameter

90.12

Finally for our example case we select a pipe of 31/2 inch size

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Confusion Story.

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We select a pipe of 31/2

But actual outside diameter is

4 inch

Dia Nominal is 90, we can say

it 90 mm that is equal to 31/2

inch

Diameter for calculation is

101.6 that is equal to 4 inch

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Size Standards

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There are different ways to express pipe size

1. Custom Pipe Size

2. NPS (Nominal Pipe Size)

3. DN (Diameter Nominal)

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Confusion Story.

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In early 18th century pipe were made & Sold on basis of internal

diameter and thickness was not important because there were no high

pressure applications.

If you ask a pipe manufacturer to give you a pipe of 4 inch he would

give you a pipe of 4 inch internal diameter but its external diameter

would be some higher.

This condition is expressed in next slide

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Confusion Story.

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4.5 inch 4 inch

every manufacturer in the town make 4 inch pipe as 4.5 inch outside

pipe. The addition 0.5 inch thickness was same which later considered

as Standard

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Confusion Story.

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With invention of Steam Engine and other high pressure applications there was a demand of thicker pipes

Pipe manufacturer had two options now,

By keeping the same internal diameter philosophy, they could now

increase the pipe thickness towards outside as

4 inch 5 inch

But they did not do that, why ?

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Confusion Story.

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There were three strong reasons

1. Their equipment like rolling machines and others were designed

to produce single outside diameter pipe, now if they increase

outside pipe diameter they have to upgrade all their production

lines, it was like building a new factory

2. They were also manufacturing pipe fittings most importantly the

valves. In case they increase outside diameter of new pipes they

also have to upgrade their valve manufacturing units also.

3. The new larger outside diameter pipes would be difficult to

installed in already existing piping systems

So, what they all decided ?

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Confusion Story.

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They keep the outside diameter same and increase the new thickness

inwards as

4.5 inch 4 inch 4 inch 5 inch 3.8 inch 4.5 inch

Previous They can do They actually did

So the new 4 inch pipe was neither remained 4 inch from outside nor from inside,

therefore a new nomenclature was invented called NPS nominal pipe size which is just the approximation of the size.

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Confusion Story

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A new system of pipe size identification was introduced called

Nominal Pipe Size or NPS.

This shows only a number without any unit

NPS-4 means it is pipe which has APPROXIMATELY 4 inch

size no matter whether it is inside diameter or outside

diameter

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DN (Diameter Nominal)

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NPS = American Standard for pipe sizes based upon inches

DN = European Standard for pipe sizes based upon millimetre

DN is just a more simplification of sized for easy understanding

DN-100 is a pipe of approximately 4 inches but 4 inch = 152.4 mm

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Confusion Story.

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There

Thickness Increases

Outside Diameter Same

114.3 mm = 4.5 inch NPS-4 is a pipe which is

approximately equal to 4

inch but actually it is 4.5

inch outside and different

diameters inside

depending upon

thickness

An approximation of 4 inch

in mm

4 inch = 101.6= DN-100

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http://www.mycheme.com/standard-pipe-sizes/

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(Custom)

(Old manufacturers)

(NPS,DN)

(New manufacturers)

Pipe size shall equal to

Inside Diameter Pipe size shall equal to outside Diameter

I will make 6 inch diameter pipe

as 6 inch inside diameter

You shall make 6 inch pipe as 6 inch

outside diameter , why you confusing

I have lot of my customers

using same size pipes, I will not

change my machines also

You are making people fool by

selling a 6 inch pipe which is

actually 6.6 inch wide

You are fool because 6 inch is from inside of pipe not from

outside, people should know before buying this.

But pipe are fitted from outside not inside

But flow of fluids is from inside not outside You are idiot

You are idiot

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Confusion Story.

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This situation continued until these standards were widely adopted

and were difficult to change, now, wherever you go you will find a 4

inch pipe equal to 4.5 inch outside.

This confusion is only for pipes up to 12 inch because above 12 inch

pipes were rarely manufactured.

But when new larger pipes came into the market this confusion was

removed .

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CONCLUSION

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CONCLUSION

For 1/8 inch to 12 inch NPS < O.D

For 14 and onward NPS = O,D

Most Common method today is NPS with thickness (Schedule No)

END

Pipe Size Calculation with Different Size Understandings is Completed

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END of Lecture-1

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Coming up next

WHO decides the Pipe Thickness

&

HOW