Welding Different NPS Together W/O Reducer

DGrayPPD · Oct 31, 2019

Good morning everyone,

I have a quick question regarding the image below. The line below is part of a glycol-water system, 304 SS material. The silver piping is 1" NPS SW and the magenta valves are 3/4" NPS SW. Operating conditions are 44 psig and 25 deg. F. The valve on the left side will transition to tubing and continue running back to two separate compressor KO drums. The valve on the bottom is just a bleed.

We recently sent the package off for approval and part of the Client's comments were that they wanted to change the 3/4" SW valves to MSW x FSW, and eliminate the 1"x3/4" swages. What they're thinking is that the MSW end will just fit inside the 1" socket on the cross and they'll just weld that together. I honestly don't think I've ever heard of someone wanting to eliminate the reduction fitting and just weld two different size pipes together. Obviously, I know the 3/4" MSW end will fit inside the 1" socket, but are there any welding concerns that I may not be aware of.

Since this is such an oddball request for me, it's one of those situations where I don't know what I don't know, so I'd just like to do my due diligence before proceeding.

Thanks for all your help.

"The only limits in life are those which we impose upon ourselves."

DVWE · Oct 31, 2019

From a welding standpoint, there is not a problem with doing this, as long as you get a good fit, proper SW gap, and two weld pass minimum per joint.

From a design standpoint, in my opinion, that is a question for the valve manufacturer.

Honestly, the pressure and temperature you stated seem well within reason to approve such a request.

The devil is in the details; she also wears prada.

jdonville · Oct 31, 2019

If the desire is to move the 3/4" valves closer to the X-fitting, then I might suggest upsizing the valves to 1" and put the reducers to 3/4" on the other side of the valves. If the desire is just to be clever or frugal, then it seems to (ignorant) me that it is a recipe for problems to omit the reducers if using reducers is customary.

DGrayPPD · Oct 31, 2019

Thank you both for the responses.

I'm trying to get clarification as to what the reasoning is. If the reasoning is simply to keep all the 3/4" valves consistent as MSX x FSW (there are others in the project that have these same end conditions), then I would still suggest at least adding a 1"x3/4" SW reducing insert. I'm just not sure either why you'd want to skimp on such a minor thing like 2 swages.

"The only limits in life are those which we impose upon ourselves."

EdStainless · Oct 31, 2019

If you look at pipe sizes and tolerances you will see that while this is possible the change of getting a good weld fit is near zero.
I have seen people swage the end of pipe down so that they can butt it to another without an additional fitting.

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P.E. Metallurgy, Plymouth Tube

DGrayPPD · Oct 31, 2019

Got it all squared away. Just a miscommunication. The fabricator/procurer who wanted to eliminate the swages actually did want to replace them with type 1 inserts, but the PM (non piper) who relayed the message to me didn't know what he was talking about so he just said to delete the swages.

Good communication is always key. Thanks again for all your help.

"The only limits in life are those which we impose upon ourselves."

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Welding Different NPS Together W/O Reducer

DGrayPPD

Mechanical

DVWE

Petroleum

jdonville

Geotechnical

DGrayPPD

Mechanical

EdStainless

Materials

DGrayPPD

Mechanical

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