Degredation of NPT threads

[tig180]

I am inspecting an old Case steam tractor with a number of threaded (NPT) openings for pipe fittings. Other than ANSI plug gages and compliance to Sec I requirements for number of threads, is there any written standard that addresses acceptability of amounts of deterioration of the threads due to corrosion over time, i.e. is there a quantitative standard to access the condition of the threads for safety other than "gee...those threads don't look so good, but they seem to hold". I could find nothing in the NBIC that refers to specific amounts of allowable deterioration. Any constructive insight would be appreciated.Thanks

 

[unclesyd]

There are No or No-Go gauges that will confirm size. As far as deteroriation is concern this is usually a judgement call.

If there is any doubt there are NPT thread repair kits available.

http://www.nolansupply.com/bysubcat...hread+Repair+Kits &type=False&specs=True

You have to make sure it is an NPT thread form as a lot of older equipment had special thread forms in different places.

 

[CodeRef]

I would determine (find) the thread specification to which the design is based and follow the tolerances given within that specification. I could suggest a spec but I am not familiar with the application enough to provide it.

You are correct that the NBIC only states what to do when discovering damaged threads. In my opinion, if your final decision is based on a judgement call it should be based upon a reference document.

Good question! Just be prepared to defend whatever decision you make.

Go/No-Go is what I think unclesyd was referring to instead of No/NoGo..... Which reminds me of ....Heads I win, Tails you lose...! Good One Uncle!

 

[unclesyd]

I wonder why I was selling a lot of taps and dies lately.

Appreciate the correction.