multiple allowable stress values for N08020 same product

[kevlar49]

Why are there multiple stress allowable values for the same product form (seamless tube or welded tube) of alloy 20Cb3 (N08020) in the 2007 edition of ASME BPV code?

 

[SnTMan]

kevlar49 it is related to allowable levels of permanent strain. If you have the book, see note G5.

Regards,

Mike

 

[U076762]

Greetings,
Don't forget to look at the other notes. Some specs list both seamless or welded tube and provide the allowable stress for seamless in the table and note derating factors to be applied depending on the type of welding used during manufacture (e.g., single weld 0.85, double weld 0.8, etc. Same for pipe.

Best Regards,
Bill

 

[LSUME]

I believe the allowable stress variation is due to the manufacturing process, which can be cold worked or hot finished, with the cold worked having the higher allowable stresses. This should be fun for the material procurement guys, especially since they (ASME) don't differentiate between the two.