Pipe Wall Minimum Thickness less than 1/16" when Threaded----ASME Section VIII Issue

[svengali81]

Hello All,
Long time looker, first time poster. I am running into an issue when using smaller diameter SCH 40 threaded pipe on ASME Section VIII Div 1 vessels. With wall thickness rather small for 1.5" and less pipes for SCH 40 when you add thread tolerance I get a wall thickness less than 1/16", which is not allowed per ASME for Section VII. Has anyone run into this issue before and have an explanation? Do I really need to upgrade all threaded connections on vessels to SCH 80?

Thanks!

 

[TGS4]

Yes, I have ran into it before. No, there is not a very convincing technical argument. Yes, it is in the Code, so yes, you have to upgrade your nozzles.

 

[svengali81]

Thank you TGS4, and that is frustrating.

 

[KernOily]

Typical argument I've heard is the remaining wall thickness left at the root of the thread leaves nothing for corrosion. Also in my experience most owners pipe specs and vessel specs won't permit ANY threaded nipple 2" and smaller to be less than Sch 80 just as a matter of policy.

It's kinda like the 45 degree bevel cut on a PSV tailpipe outlet. There's no science behind it but everybody does it because it's sacred tradition.

Sometimes you just got to go along to git along.