ASME B31.1 Min Wall Calculation

[TylokInternational]

Hi,

I'm trying to perform the min wall calculation on parts that contain male NPT and female NPT threads. What diameter do you use for the calculations? For female NPT thread, I've been using the E3 diameter + thread height. For the male NPT threads, I've been using the E2 diameter + thread height. Is this correct? My assumption was that I should use the diameter after make-up of the threads since that is what would be exposed and not reinforced.

Jason

 

[rumandcola]

For the female thread set your inside diameter to 'D' and for the male thread set your outside diameter to the minor diameter at the small end of the pipe 'Ko'. This creates the least material condition.

 

[TylokInternational]

If the part is screwed into a mating part though, wouldn't that change where the effective min wall would be?

 

[rumandcola]

Depending on the amount of torque applied, that would control how far the threads are engaged. I am not sure how you can predict where the pressure actually seals in a tapered pipe thread joint. Depending where the effective seal occurs, would determine the effective minimum wall occurs. For that reason you should design for the least possible material condition based on the variables in my last post.