## WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

## WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

(OP)

I have 48" API 5L GR. X52 LSAW PIPE, Design temperature is 75 deg C, design pressure is 138 bars & corrosion allowance is 3mm. When calculated wall thickness using formula t= PD/(2SE+PY)I got result as Wall thickness = 70mm? Is that true? we can't find pipe with such thickness. What will be the exact WT required under such conditions?

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

However I don't know what you're using for "E", if you're applying any temperature de-rating factor (unlikely at that temperature but you never know) and have no idea what "Y" is. Keep your units consistent as well for pressure and yield strength.

However based on 13623, E of 0.72, Y=1, S = 360, with the 3mm CA I get a t min (you need to allow for manufacturing tolerance with 13623) of 34.61mm Still pretty thick, but its a big pipe and a reasonably high design pressure.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

Wall thickness can be find out using ASME B31.3 (304.1.2 STRAIGHT PIPE UNDER INTERNAL PRESSURE) by following equations;

t = PD/2(SE+PY) - (3a)

t = PD/2SE - (3b)Barlaw's Formula

t = D/2(1-Sq(SE-P/SE+P) - (3c)Lame Equation

t = P(d+2c)/2[SE-P(1-Y)] - (3d)

I have taken eq.(3a) from above to calculate wall thickness.

GIVEN INPUT FROM CLIENT:(Line Size = 48", Material: API 5L GR.X42, Design temp: 75 deg C, Design Press: 92 bars, Hydro test Press: 138 bars)

For calculating WT, t = PD/2(SE+PY),

Where, P = Design pressure (taken Hydro test pressure as 138 bars = 2001 psi = 2.001 ksi)

D = Pipe Outside Diameter = 48"

S = Allowable stress = 20000 = 20ksi (ASME B31.3 for API 5L X42)

E = Quality Factor = 1 (ASME B31.3)

Y = Coefficient = 0.4 (ASME B31.3)

= 2.001x48/2(20x1+2.001x0.4) = 2.308 Inches = 58.64MM

CA = 3MM

SO WT = 62MM

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

Is it X 42 or X 52? Not that it matters much with 31.3 as it makes no difference to the allowable stress in B 31.3, which is why I assumed you were using a pipeline code.

Forget about hydrotest pressure - the key one to calculate wall thickness on is DESIGN pressure - read the definition in 304.1.1 - gives you a more manageable 42.6mm inc CA

Otherwise you seem to have it correct.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

Now may I ask should we go for X42 grade or higher grades likes X52 or X70 for all items?

If we consider thickness based on design pressure only, how about hydro testing? we should omit hydro test pressure ( 1.5 Design pressure)?

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

You can use the pipeline codes in certain facilities, but then need to buy your flanges from the same grade steel as the pipeline.

The hydrotest pressure is taken care of within the allowable stress figure (31.3) or the design factor (pipeline codes) and you don't miss out a hydrotest.... Calculations for design are normally the design pressure.

Figure out which design code to use and then work from there.

Also: There's usually a good reason why everyone does it that way

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

Could you please figure out which design code you are meant to use? & hydro test pressure?

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

Choosing design code is an important design issue and should be discussed and agreed with client / owner at the start of the work.

Hydro pressure is set by the code you are using. 31.3 is normally 1.5 times design / MOP. Other codes have different multipliers.

what and where is this skid going to be used??

Also: There's usually a good reason why everyone does it that way

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES

## RE: WALL THICKNESS CALCULATION FOR LARGE DIA PIPES