RE: [PipingDesign] How is Tensile Strength Established by Tube Spec?

From: <Ken>
Date: Thu Jan 17 2008 - 13:04:00 EST

Chris -

Chris -

Thanks for the guidance on using Sect. VIII for a one-time substitution. I have not needed to pursue this before and getting pointed to what part of the code could address this helps.

One tubing manufacturer agreed that this material has been in use for years, that it is the same tube as one that is Listed, except for tube finish, and that they have been unable to convince the B31.3 committee to List it. I want to check into how a material gets Listed, and Sect. VIII may shed some light on that too.

From: [] On Behalf Of Christopher Wright
Sent: Tuesday, January 15, 2008 7:23 PM
Subject: Re: [PipingDesign] How is Tensile Strength Established by Tube Spec?

On Jan 15, 2008, at 4:45 AM, Ken Nisly-Nagele wrote:

> So, I think either the purchase spec must state minimum Tensile
> Strength
> and minimum Yield Strength in accordance with specific test methods
> (e.g. ASTM A 370), or the Supplementary Requirements to A 270, which
> does state Tensile and Yield Strength requirements, must be specified.
> Then the allowable stresses in accordance with Para. 302.3 can be
> determined.

You can probably get guidance from Section VIII Div1 as to what exactly you need to do. I don't have a copy of Section VIII handy, but the relevant section is somewhere near the front where general material requirements are noted. The Appendix dealing with roughly the same issue addresses requirements for listing a material in Section II--that's not what you want. You're after a one-time substitution.
> Would not such properties such as elongation and
> hardness also have to be specified?

The problem you may run into is that the tube you get may be work hardened to increase its strength. This is common with austenitic stainless, but all that work-hardening vanishes when it's welded. Most pressure tubing specified in the Code is annealed. Of course with thin wall tubing that affects the buckling resistance enormously, both resistance to collapse under external pressure and dinging from abuse.

I've run into this a couple of times with food processing--hard to make these people understand that structural response is as important as it is.

Christopher Wright P.E. |"They couldn't hit an elephant at chrisw@skypoint. <> com | this distance" (last words of Gen.

.......................................| John Sedgwick, Spotsylvania
http://www.skypoint <> .com/~chrisw/

[Non-text portions of this message have been removed] Received on Thu Jan 17 13:04:00 2008

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