Machining of NPT Couplings?

[posture]

Hi

My fabricator has requested that we use couplings machined from SA 516 Gr 60 instead of forged 3000lb couplings from ASTM A105.

I've looked in ASME VIII and B16.11 and can't find anything related to this. Is this allowed?

Design pressure is 10 bar and desing temp is 90 deg C.

regards

posture

 

[fegenbush]

Yes, it can be permitted, but proof testing may be required, depending on the AI. I have done this when couplings are not available in the required materials.

However, I would ask why they would like to do this. One possible reason would be because of low MDMT. If this is the case, SA-350 LF2 couplings could be used. These are chemically the same as SA-105, but are impact tested.

 

[austsa]

I generally find that couplings are A105N, so suitable for low temp use. Perhaps client prefers lower strength for some reason. I'm curious to the reason as well.

 

[europipe]

Maybe the material is on stock?

 

[fegenbush]

Austsa,

Just because the SA-105 is normalized, it does not mean that it is impact tested. The material test report would have that information if it were. If you wanted to buy extras from that heat/lot and impact test them at the desired temperature, that would solve the problem, but the possibility exists that they do not meet the necessary toughness requirements.

 

[posture]

Thanks for the replies.

It turns out that the reason the fabricator has requested this is becasue the have prepped the hole in the head to the wrong dimensions and the A105 coupling is now too small to be welded in! they have SA 516 GR 60 in stock hence their request.

Posture

 

[SnTMan]

posture, under those circumstances, I doubt I would permit a connection made from plate. Barstock or preferably forged bar.

Or properly plug the hole and try again

Regards,

Mike

 

[Duwe6]

Open the hole up a little. Like SnTMan, I think substituting rolled plate for an item specified as forged is a very bad idea. "I have this on hand, can I use it?" is a terrible reason to substitute lower grade materials.

 

[rhg]

Try with class 6000 coupling and increase inspections on your fabricator.

Regards

rhg

 

[austsa]

fegenbush,
Agree with your comments. Generally, I find that when the manfr goes the extra step to normalise, he also gets it impact tested. austsa.

 

[rhg]

Posture

I´m curious. Please, can you tell me the nominal diameter (NPS) of these couplings ?

Regards

rhg

 

[PVinspector]

The question was: Is it allowed? (assuming here for VIII Div.1)

The answer to that question is: Yes.

Other comments are related to whether it is a good idea or not. IF UCS-6 of Section VIII-1 had restrictions on plate for pressure. What is not prohibited is allowed.