Re: Piping MAWP

The basis of the code equation to determine the min. wall thickness is the design pressure (not operating) and the allowable stress of the material at temp.
add the ca and factor-in the manufacturing tolerance and then you have now the min. reqd thickness. Select the nearest allowable pipe sched and you end having the nominal wall thickness.

To calc the MAWP, you work backward as stated by you. Deduct the ca from the nominal wall thickness rearrange the previous equation and solve for the pressure. The calculated pressure is now your MAWP based on the nominal thikcness less the ca.

If you can figure out the hoop stress, you dont even need the Code eq. to figure both values.

My question is this. If you figure out the MAWP of the pipe and it exceeded the MAWP of the vessel connected to it inlcuding the P-T rating of the flange joint, what will be the proper setting of the PSV - the MAWP pipe, MAWP vessel or the flange rating? The data sheet of the pressure vessel do not mention the MAWP but only the test pressure.

• Original Message ----- From: "tnmngilman" <tnmngilman@yahoo.com> Date: Tue, 18 Mar 2003 12:38:18 -0000 To: <a href="/group/PipingDesign/post?postID=4tOB6cOWS3WW94bIMXhWAc09_FBo-bg14RAA9C7BFcNcWeTtxuSHxPOp-3rg7SQLip9nLOhti30Mosu-5goOTz_gZjs">PipingDesign@yahoogroups.com</a> Subject: [PipingDesign] DESIGN

> I don't design for a living, so my apologies if this seems like a
> basic question. I'm trying to determine the first step in design,
> and it seems to me that the desired operating pressure has to be
> known before anything else. In looking at the ASME section 1 formula
> for wall thickness, the two key unknowns are the material and the
> pressure. If you use 200 psi in the formula with a certain material,
> then this is the MAWP.
>
> The other question is: Is there an acceptable means to work backward
> to determine the MAWP? In other words, if MAWP is not known, is it
> acceptable to rate a pipe at say 200 psi if it has a successful
> hydrostatic test at 300 psi? By the book it doesn't seem proper to
> me to work backward, but if there is no documentation or marking on
> the pipe how is the safe operating pressure determined?
>
> Thank you.
>
>
>
>
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