Maximum pressure for LP threads

[jabbey]

API 6A and ASME B31.1 tell me threaded connections should not be used over 5000 psi. (I'm using 2" XXS pipe) But I can go out tomorrow and buy a hammer union rated at 10000, or even 15000 psi, with LP threads on either end. Even with ideal inital assmebly, those threads are going to be abused badly as part of a hammer union. Am I missing something? Are the standards way too conservative? Can threads be safely used at this kind of pressure?

 

[barilko]

I'm not an expert, but there are a few differences between LPT and a union.

1) The union uses a elastomer seal and it's thread does not see process fluids. An LPT seals on it's threads and is susceptible to root corrosion. I've heard of bull plugs with v-threads being launched under pressure.

2) Union threads are usually a buttress, whereas LPT is a V-thread.... I would think there is a larger shear area on a buttress thread.

3) Just as a note, I vaguely remember there being 2 versions of the LPT a long and a regular.

 

[barilko]

One other thought.... the union is a straight thread, the LPT is a tapered thread. Number of threads holding axial force is dependant on how deep it is threaded in. Depending on how big your pipe wrench is, you can also overtighten and yield the thread.

 

[jabbey]

Guess I wasn't clear enough. I'm not questioning the union itself, I'm talking about the two ends provided to join the union to your system, which often are LPT.

http://www.hammerunions.com/images/kemperimages/KEMPER_UNION_1002.gif

 

[Hush]

I’m guessing but here goes:

I noticed API 5L doesn't specify working pressures so I figure API 6A probably specifies 5000-psi max for 2 LP connections because you have no way of knowing what the material strength is of the part you screw into it. I.E. The limit is probably selected for the lowest material strength A25.

On the other hand, if you’re building frac lines for 15,000 psi you’re going to be using 75K yield pipe or higher.