B31.3 - 304.1 Wall thickness calculation inquiries

[jeffhogie]

Firstly, let me say that I am a fairly new engineer, and I am simply not confident with the following information.

I have a few different questions

1- the variable 'P' (internal design gage pressure); is this the 'upset pressure' or the 'cold-flange-rated pressure'?

2- When determining the coefficient of Y (Table 304.1.1) and coefficient S (Table A-1); is the Temperature the 'upset temperature'?

3- where/how does mill tolerance (MT = ~0.125) effect the calculations. (Note: my 'c' value is the sum of the thread/grove depth, corrosion allowance and erosion allowance)
ie. 304.1.1 eq (2) should it be;

- tm = (t+c)*(1+MT) OR
- tm = (t+c)/(1-MT) OR
- something else?

Does taking into account the mill tolerance eliminate the need to take into account the tolerance of the depth of cut?


Any help on these questions would be much appreciated,

Thanks,

- Hogie

 

[nickelkid]

First I would recommend that you obtain a book like Introduction to Pipe Stress Analysis – Sam Kannappan &/or the Practical Guide to ASME B31.3 – Woods. A class from ASME would not be out of the picture either, many are available.

An electronic version of the Practical Guide by Woods can be downloaded from

http://www.casti-publishing.com

for a fee.

 

[JohnBreen]

Hogie

You need to get a copy of ASME B31.3 and you need to read it. All the information you are asking about is in the Code. Read Paragraph 301 for an understanding of "design pressure". Understand the differences between operating conditions and "occasional" loadings (upsets). Read paragraph 302.2.4 in its entirety. Read the definitions of paragraph 304.1. for pressure design.

The 12.5 percent mill tolerance is applied to seamless pipe because the manufacturing process may lead to the wall thickness varying by that amount (12.5 percent thicker on one side and 12.5 thinner on the opposite side). You must add to that (if you are using seamless pipe) allowances for corrosion, grooving, threading, or anything else that reduces the finished wall thickness.

Look at this:

http://catalog.asme.org/books/PrintBook/Process_Piping_Complete_Guide.cfm

Regards, John.

 

[NewMechE]

I was under the impression that the 12.5% undertolerance concession applied to ALL pipe regardless of whether it was seamless or not.

 

[DSB123]

NewMechE,
The amount of undertolerance should be checked in accordance with the dimensional standard the piping is manufactured to. It is not always 12.5%!!!.


Regards

DSB123

 

[JohnBreen]

For wall thickness, seamless pipe mill tolerance is 12.5 percent. For seam welded pipe the wall thickness tolerance is that of the standard for the plate used to make the pipe.

Regards, John.