Min Wall's "Nominal Dimensions" for Stress

[StevenHPerry]

ASME B31.1 stipulates that pipe stress calculations be done with the nominal dimensions of pipe. This is clear enough for schedule pipe: 14" S-XS should use a 0.5" wall thickness in stress calculations without regard for an under tolerance on thickness.

What do you consider the "nominal dimensions" of pipe ordered as minimum wall?

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[BigInch]

In a special order for a custom wall thickness, the specified wall thickness would become the nominal wall thickness and the manufacturer would be allowed to produce that +/- the allowed tolerance.

If it ain't broke, don't fix it. If it's not safe ... make it that way.

 

[StevenHPerry]

Thanks, BigInch. I can understand how that applies for custom wall. But I would like to know for the situation where the wall is a minimum wall.

E.g. 14NPS 1.000" min wall to ASTM A335. The under tolerance is 0%, the over tolerance is either 15%, if memory serves.

What then is the nominal dimension for use in stress calculations?

- Steve Perry

http://www.linkedin.com/in/stevenhperry

This post is designed to provide accurate and authoritative information in regard to the subject matter covered. It is offered with the understanding that the author is not engaged in rendering engineering or other professional service. If you need help, get help, and PAY FOR IT.

 

[BigInch]

Never seen a definition for that one. My opinion would be the thinnest scheduled wall thickness (nominal, exclusive of tolerance) that meets the pressure requirement.

For B31.4&8 stress calculations you use the named schd wall thickness, exclusive of any +/- tolerance. Not sure if 31.1 has the same convention.

If it ain't broke, don't fix it. If it's not safe ... make it that way.