A194 Gr. 2H or Gr.7 nuts - Low Temperature Operation 1

[Fuzzbox 100]

We traditionally have specified a B7/2H combination for 'normal' piping operation (typically up 20 bar and ambient temp. conditions).

We also have a 'low temperature' requirement where the minimum temperature can reach -42degC (-44degF).

In these 'LT' conditions, we have typically specified an A320 Gr. L7 stud and A194 Gr. L4 nut combination. Our understanding is that Gr. L4 nuts are being 'superseded' by 'Gr.7'. Ok, fair enough, we'll specify Gr. 7. (Although I realise that there is a difference between Gr. 7 and Gr. L7).

But ASME B31.3 Table A-2 gives min. temps of -55degF for both Gr. 2H and Gr. 7 nuts. And A193 B7 studs also have a min. temp of -55degF.

So to my question - is there any reason why we could specify A193 B7 / A194 2H for 'our' low temperature conditions? Or am I missing something?

Many thanks.

 

[GBTorpenhow]

B7/2H is good for -55F per B31.3, as you have stated.

You may want the added warm and fuzzy of documented impact testing on the studs, which is the reason I was given when I asked many moons ago why a low temp CS pipe spec meant for LPG and cold climate service (-50F) with A333-6 pipe used L7/7L studs/nuts.

 

[Fuzzbox 100]

Many thanks for the comments.

Funnily enough, my 'conditions' are also related to an LPG/propane duty - in 'boiling' conditions, hence the -42degC.

So, just a further question - and I'm asking as I don't have the 'source' standards to hand.

I'm generally aware that nuts to A194 Gr. L7 are impact tested - I think to -150degF?

But are Gr.7 also impact tested? If so, presumably to -55degF?

 

[akpipelineengr]

Worth noting that -55 rating for B7 material only applies to studs less than or equal to 2-1/2" (which obviously covers most studs, but not all). Above 2-1/2", that rating goes to -40. Several North Slope operators have recently changed their specs to take advantage of B7 studs up to 2-1/2", but still specify L7's for larger studs.

 

[GBTorpenhow]

Going from memory but as I recall grade 7/7L nuts are mechanically and chemically identical, only difference is the L marked nuts have been impact tested to -150F. Same for B7 and L7 studs.

Portland Bolt has a very good catalog of technical data on bolting materials on their website.

 

[Fuzzbox 100]

Thanks, guys, for your comments.

Fortunately, our studs are only 3/4" max. so the -40 criteria (for B7's) doesn't apply in our case. But useful to know.

And thanks 'GBT' for pointing me in the direction of the Portland Bolt resource. Some very useful information on there, including comment on the Gr. L vs. Gr. L7 question.

https://www.portlandbolt.com/technical/faqs/grade-7-vs-grade-7l/