Dual Rated Pipe & Fittings 2

[magusinp]

Whenever we receive pipe & fittings dual rated as "316/316L", for example, does that ALWAYS mean that the allowable stress will be the HIGHER rating of the two? The pipe distributor said it's true & I looked at a few MTR's and the mechanical test Tensile Strength & Yield Strength were the higher values. I need to know if I can go ahead and design base on the higher value.

 

[metengr]

If pipe or fittings are dual certified for use, yes you can take credit for the higher strength value. What is your application regarding allowable stress or are you interchanging allowable stress value with tensile strength on the MTR?

 

[stanweld]

Temperature limitations are imposed by a number of Codes which mandate minimum carbon content. So as long as the design temperature is less than that requiring a minimum .04% C content; e.g. B31.3 Appendix A Notes 27 and 28. In short you must check the design allowables in the the applicable Code.

 

[magusinp]

Thank you all for your help. metengr, stanweld, I am not using the MTR values for anything except to verify that the pipe was rated to the higher tensile strength. The allowable stress from Table A1 of B31.3 is the applicable value. It's just that the difference between the allowable for 316L and 316 is 3300 psi!
By the way, I am in the unenviable position of verifying the Code conformance of a design that's been in use for 50 years but evidently no one ever actually qualified it. So I sincerely want to be able to show that the legacy design is safe.

 

[metengr]

I would use a limiting or more conservative approach, such as either lower allowable stress value or service temperature limitation as mentioned by stanweld in Table A-1, if applicable, in B31.3 for evaluating dual certified material. If the limiting condition(s) is acceptable, this would indicate the design is safe for dual certified material.

 

[Linepipe]

Dual certified materials can be used at either rating. In your case you will want to look at the welding that was used to ensure the welds are not the limiting factor.