Need review for pipe wall thickness calculation sheet for pipes under internal pressure 7

[Asisraja D]

Hi professionals

i am a project engineer and i did some calculations part for calculating wall thickness for pipes under internal pressure as per ASME B31.3.
i have attached the sheet here.

This is just my work to submit to all of you for a review on the steps involved here and the Units i used here whether right or wrong ?
if anyone cross check the work please you can download and try this at free time. Thank you for all of your support to keep curious of engineering as part of my life.​

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[XL83NL]

Such question is better asked internally in your company to your mentor. How can you defend a situation where, for a stress critical item, the calculation was verified on the internet by an unknown person? Also, bear in mind people here are willing to help with specific questions, but this is just too basic.

Huub
- You never get what you expect, you only get what you inspect.

 

[Asisraja D]

XL83NL

it is correct when you have same minded people with enough members to check the design parameters in any organization but unfortunately this is not happening for me because we have only few people to work in a project and pipe wall thickness is selected based on manager's experience so i need someone to review the calculation steps involved here. i have got some details in calculation in this forum so i may be clubbed the information in a sheet for easy understanding for all. This is just my request for you people when you have a free time, just have a look in this then it will be a help for all who really need this even when it is too basic.

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[LittleInch]

It looks ok, but stick to the units in the code which I think are psi, not ksi. The two might balance off, but you can go horribly wrong.

Also stay in one set of units until the very end as that can also go horribly wrong when you mix mm and inches etc.

But it is crucial this is checked and approved by a competent engineer in your organisation.



Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Asisraja D]

LittleInch

The table shows allowable stress value in ksi for Fahrenheit units.

so i took internal gauge pressure also in ksi only and stress value for Fahrenheit for maintaining uniform units till end.

i haven't changed the units. i am clear while adding them.

thanks for spending your time for reviewing my sheet.

But it is crucial this is checked and approved by a competent engineer in your organisation.
There is no any team to check the design in our organization, that's why i am doing this kind of stuff when i have free time to ensure at least minimum safety before execution of some projects.


"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[NovaStark]

One thing you can do with these types of spreadsheets, is to manually calculate one of the thickenesses. If your answers match (within reason due to rounding), then you know your formulas are correct.

When I had to do these types of repeated excel calculations with more complicated formulas, doing one example manually has saved me many times!

Additionally, one thing that would be important to keep in mind is that the tolerences for piping may vary based on the grade or type. For example, seamless piping might have its thickness vary by +/- 12.5% but welded piping may be +/- 0.1 inches.

So knowing what piping you are dealing with will be important.

 

[Asisraja D]

NovaStark

So knowing what piping you are dealing with will be important.

of course, i will sir.

but i don't know whether this kind of stuff will be useful in project engineering (mechanical)career. Anyhow i will keep review my work before the execution at site on my own to avoid some errors.

Thank your sir.

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[Snickster]

I have checked your calculation with my calculation spreadsheet and have the following comments:

The required wall thickness of 1.4746 mm is exactly what I calculate. Your equation and input parameters are correct.

The calculated wall thickness with "c" value is correct adding 3 mm to calculated value

The specified wall thickness is not correct. The table you show for wall thickness A53/A53M-10 is only a table which gives wall thickness permissible if you are inspecting a shipment of pipe from a manufacturer. The actual minimum wall thickness allowed to be sold by the manufacturer is 87.5% of the nominal quoted wall thickness. For your case if you are purchasing pipe with a stated nominal 4.78 mm wall then the mill tolerance is 12.5% meaning that you may get a wall of 0.875 x 4.78 = 4.1825 mm, and if the inspected wall upon shipment is less than this then the pipe is rejected by the buyer since it is greater than the allowable mill tolerance per A53 pipe specification. That being said the selected wall thickness must be such that after multiplying by 0.875 mill tolerance you still have a wall greater than the required value of 4.4746 mm (0.176 inches).

The closest standard pipe wall thickness for 10 inch carbon steel pipe to A53 specification is Sch. 20 with nominal wall of 0.25 inches and with 87.5% mill tolerance a minimum wall of 0.219 inches as received from the manufacturer. This is greater than the required value of 0.176 inches calculated so this would be the selected pipe. I calculate the maximum allowable internal pressure for 10 inch Sch 20 with mill tolerance and corrosion allowance considered is 378 psig.

Furthermore in hazardous services such as chemical plants and oil and gas facilities most clients use Standard wall or Sch. 40 as a minimum for mechanical strength requirement in process piping rather than just select pipe wall based on internal pressure. For 10 inch Sch 40/STD the nominal wall thickness is 0.365", the minimum wall with mill tolerance is 0.319" and the MAWP is 761 psig.

 

[Compositepro]

That is a wonderful reply.

 

[Asisraja D]

Snickster

you are right as per ASME B3636.10M also shown the wall thickness for 10" pipe for sch20 is 0.25" (6.35mm).

if so should i consider this is as specified wall thickness (ts) in my calculation ?

then i will get 6.35 mm X 0.875 = 5.56 mm as minimum permissible wall thickness (tm) as you already told.
so still we are the decision maker to select the suitable wall thickness like sch20 or 40.

the minimum wall with mill tolerance is 0.319" and the MAWP is 761 psig.

how did you calculate MAWP is 761 psig for 0.319" ?





"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[Snickster]

you are right as per ASME B3636.10M also shown the wall thickness for 10" pipe for sch20 is 0.25" (6.35mm).

if so should i consider this is as specified wall thickness (ts) in my calculation ?

Yes this is the specified or selected wall thickness.

then i will get 6.35 mm X 0.875 = 5.56 mm as minimum permissible wall thickness (tm) as you already told.

Yes 5.56 mm would be the minimum as-received pipe wall thickness of nominal 6.35 mm wall pipe supplied by the manufacturer. So the calculated wall thickness with corrosion allowance has to be equal to or less than this value.

so still we are the decision maker to select the suitable wall thickness like sch20 or 40.

Yes

the minimum wall with mill tolerance is 0.319" and the MAWP is 761 psig.

how did you calculate MAWP is 761 psig for 0.319" ?

For 10" STD ts = 0.365" wall pipe, the minimum wall thickness in the as-received condition from the manufacturer is 0.319" = tm. Minus 0.118" for corrosion allowance = 0.201" = t. This is the available wall thickness to resist internal pressure. Substitute this value in your spreadsheet equation and solve for P.

 

[Snickster]

Also using your spreadsheet you can set ts = 9.271 mm (0.365") and then keep increasing the design pressure until tc = tm.

 

[Snickster]

Note also that in the green highlighted box for tm, this should be noted as "minimum wall thickness of as-supplied pipe". The "minimum permissible wall thickness" = tc.

 

[Asisraja D]

Substitute this value in your spreadsheet equation and solve for P

0.201" = t = 5.10 mm.

t = P * D / 2 (SWE + PY)

5.10 = P * 273 mm / 2(20 * 1 * 1 + P * 0.4)

here the variable is P internal pressure but it is by default divisible in this formula.

how can i substitute that ?

sorry it might be a basic mathematics, so please can you explain me a little bit.


"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[Asisraja D]

Snickster

Note also that in the green highlighted box for tm, this should be noted as "minimum wall thickness of as-supplied pipe". The "minimum permissible wall thickness" = tc.

yeah , i have changed that.


"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[Snickster]

Solve for P

t = P * D / (2 (SWE + PY))

P = 2t*(SWE + PY)/D

P - (2t/D)PY = 2t*(SWE)/D

P*(1 - (2t/D)Y) = 2t*(SWE)/D

P = (2t*(SWE)/D)/(1 - (2t/D)Y)

 

[LittleInch]

My point about units is that very few people will use ksi as a number for internal pressure. so use 20,000 for S and it will all work out.

Also you mix and match mm, inches and psi with some factors. Far better to stick to the units used in the original equations. Appendix J lists these for ASME B31.3

This might work out here, but other equations it won't, especially if there is a fixed factor or number in the equation.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[fel3]

LittleInch…

Excellent commentary about units. Calculations like this justify using Mathcad or Smath.

============
"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[Asisraja D]

Snickster

Thank you so much sir. This is going to help a lot of people like me.

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce

 

[Asisraja D]

LittleInch

Sir as you told i would be careful while using the units and it is really very useful for me. thank you sir.

"Strive for perfection in everything you do. Take the best that exists and make it better. When it does not exist, design it." - Sir Henry Royce