WALL THICKNESS CALCULATION FOR LARGE DIA PIPES 1

[robs123]

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?

 

[LittleInch]

This looks like a student post? Please convince me otherwise as it is a very simplistic question.

My motto: Learn something new every day

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

 

[robs123]

The design conditions are correct, this is required for our fabrication in our project. LittleInch pls explain if you can

 

[LittleInch]

It looks like you're using the ISO 13623 equation rearranged for t, but you don't specify.

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

 

[robs123]

I have taken equation for wall thickness using ASME B31.3 - PROCESS PIPING where most people are using to check WT, & not ISO 13623.

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 CLIENTLine 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

 

[LittleInch]

If you provided this info to start with it would have been a lot easier....

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

 

[robs123]

Thanks for your answer. Actually this is required for our skid manufacturing in high pressure transmission line. Our client have asked to take material as: For Flanges: ASTM A694 F42 - F70, Fittings: A860 WPHY 42 - 70 & Pipes: API 5L LSAW only. So we planned to take pipe material as premium grade b/w (X42 - X70) according to the availability & costing. We have concluded to take 42 grades for all PIPES, FLANGES & FITTINGS, which is cheaper compared to 52 or 70 grades.

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)?

 

[LittleInch]

Your problem is the use of ASME B 31.3. This code works in a different way to pipeline codes and in general gives you very little credit for using higher strength steel so using X 42 is OK, but watch out for changes in ID if any parts of this are piggable.

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.

My motto: Learn something new every day

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

 

[robs123]

We are designing as per ASME B31.3.

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

 

[LittleInch]

You can use any design code relevant to the location and the substances. B31.3 is a very common code to use for topsides, plants and facilities for hydrocarbons. However if there is a substantial amount of large diameter high pressure pipe, then one of the pipeline codes can be used for pipework which reduces wall thickness because although the design factor is lower than for the pipeline, the increased SMYS of the pipe material brings the wall thickness down compared to 31.3. It's only normally worth doing where you have very high pressures or a lot of large diameter pipe.

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??

My motto: Learn something new every day

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

 

[robs123]

Thank you very much for pointing me in the right direction on this.

 

[LittleInch]

You are welcome.

 

[meca103]

You could declare high pressure and use chapter IX, 2000psi is on the low side but it is up to the owner to declare high pressure. S will change to 2/3 of yield = 34.6 ksi for X52 material.