Pull Strength of 2-inch NPT Threads
Pull Strength of 2-inch NPT Threads
(OP)
I'm designing a gas-knockout that has a 2-inch NPT coupling right where I would put a lifting eye. The knockout weighs about 1,000 lbm and I was thinking about fabricating a lifting eye that would thread into the NPT threads. I've been searching for data on the pull strength of cold-rolled NPT threads all morning without much success.
Anyone have this information? I know that I've lifted more weight than that with piping that was screwed tight into NPT threads, but I don't want to have to screw the lifting eye in till it is pressure tight.
David
Anyone have this information? I know that I've lifted more weight than that with piping that was screwed tight into NPT threads, but I don't want to have to screw the lifting eye in till it is pressure tight.
David





RE: Pull Strength of 2-inch NPT Threads
If you do manage to find a value for pull-strength, it could be based on perfect conditions. But, since you cannot properly torque that fitting and since the condition of the threads may deteriorate over time, you could be creating a hazard for future lifts.
I was not aware that there was a machine to cold-roll a female NPT thread. All of the ones I have seen have been cut threads. If you are referring to the male threads on the lifting eye, I assume that this would have to be straight threads. Are you proposing using straight threads on the male into tapered threads on the female? If so, I am sure that there are other experts out there who could speak to that point.
Johnny Pellin
RE: Pull Strength of 2-inch NPT Threads
Thanks for your input.
David
RE: Pull Strength of 2-inch NPT Threads
jt
RE: Pull Strength of 2-inch NPT Threads
During WWII the lifting plugs for bombs were made from Malleable Iron. From my recollection the early ones were NPT threads while the later ones were straight pipe. These plugs plugs were screwed into both CI and CS in up to 1000 pound bombs. The testing of same used a tool steel die as a hold down and as I recall the safety factor was better than 2::1 and the actual test were at least 3::1.
I tend to recall the AAR also has a pull out requirement on their Malleable iron fittings.
To the more modern stuff. Flat face pipe flanges are use for various construction items, like railings and rack tie downs.
RE: Pull Strength of 2-inch NPT Threads
That is an interesting way of looking at it. I started off thinking that this was a trivial question that I just wasn't getting my head around. Sounds like there are multiple ways to go at it. Thanks.
David
RE: Pull Strength of 2-inch NPT Threads
RE: Pull Strength of 2-inch NPT Threads
David
RE: Pull Strength of 2-inch NPT Threads
RE: Pull Strength of 2-inch NPT Threads
Agreed. That's why I prefer end caps. They're much classier!
jt