Welding valves with sensitive internal gaskets 1

[Stefan2211]

Dear All,

what is the common practice to socket weld valves with internal gaskets e.g noeprene, N-Butan. The heat impact can damage the gaskets. The supplier does not provide a clear instruction other than "use heat sink or other method to avoid damage".
There are many ways to do it but what are your preferred and daily method to get it done. Attached 2 samples; control valve with installed PTFE gaskets in the body and check valve with neoprene gasket.
Thanks

 

[akpipelineengr]

The most common way I seen is using metal seated valves and avoiding vulnerable soft goods entirely. Or using flanged valves.

Your control valve example didn't upload, but that check valve is available with metal-to-metal seat option.

 

[TugboatEng]

PTFE will tolerate temperatures up to 550°F. At that temperature stainless steel will turn a straw gold color. It should be fairly easy to make the weld without the body of the valve turning gold in color. Buna and Neoprene can also tolerate transients to very high temperatures but neither rubber has a long service life so I would hesitate to use them in permanent non-serviceable installations.

 

[Stefan2211]

TugboatEng,
The design was chosen due to the process parameters; 100% welded and gaskets acc. to media requirement. No alternative possible.

 

[DVWE]

There are many ways to do it but what are your preferred and daily method to get it done.

Most socket welds require two weld passes, so recommend to your welders that they weld quickly, with as small as welds possible.

If possible, blow a small amount of air through the assembly during welding. Immediately after welding, blow air directly on the outside as well.

A tight fitting clamp type heat sink with a similar ID as the valve OD works well, but can be difficult to make/find. Think of something shaped like a doughnut that can be separated into 2 halves and clamped or screwed together.


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

 

[Stefan2211]

Hi DVWE,
that's the only I agree. We do carefull welding now and let the valve cool down. Alternatively we used a wet rag and kept the body cool.

 

[bcd]

There is no "common practice" Some chose to take the valves apart to avoid melting the seals, and others chose to weld with the valve fully assembled. There are pros and cons for each.

One place I worked initially demanded all socket weld valves be disassembled before welding. A high percentage of the valves leaked after installation because of body distortion from a large weld and errors during reassembly. Reusing gaskets, missing parts, parts installed incorrectly, improper tightening of bolts, etc. Then they tried welding fully assembled valves. Smaller welds over a few passes, with temperature checks between passes. Wet rage around valve body and low-pressure air flowing through the valve and into downstream pipe, drawing the heat away from valve. Welding takes longer but is offset by the time to take the valve apart and reassemble. The study revealed a lot fewer leaking valves when welded fully assembled. About 10 times less. So that is the standard practice now for this company.

 

[kingnero]

If possible, blow a small amount of air through the assembly during welding. Immediately after welding, blow air directly on the outside as well.

What is the valve material?

 

[DVWE]

What is the valve material?

Good question. Thats why I stated “if possible”.

Regardless, it can’t be any worse than a wet rag, as the OP has stated is already being done.

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

 

[dvd]

Depending on how wet and how much rag, there is a possibility to introduce hydgrogen into weld metal.

 

[3DDave]

All I have that is helpful is that the welder is the most important component.

We had a re-procurement on an existing product and farmed out the weldment. We'd already made 90 of them. This company called repeatedly to say the product was impossible to make and the drawings had to be changed. So we made a plant visit. The welder was Air Force aircraft repair qualified - no problem with porosity or prep. But every weld was really huge, which is not what a sheet-metal product normally needs.

So we assured them this was already built, sold, and in regular operation. Ended up contacting the guy who did the original welding and he agreed to come out for a few days to walk the welder through it. Apparently eyes were really wide over the value of a light touch and good speed; no dawdling. Seriously cut the cost of the filler rods that had been smoked on the first samples. Like, no you don't need another 5 pounds.

Result - we changed not one speck on the drawings to accommodate the original weld technique and they cut 80% of the weld time and the amount they were spending on filler rod.

 

[mfgenggear]

There is no dimensions but from the lettering it appears to be small diameter.
There needs to be a weld end manufacturing engineer, and a welder involved with the procedure.
In my aerospace days,
I built fixtures for lox fuel lines. I designed welding fixtures to hold the details in place. Welding flanges to tubing and other components. But all of this was with the current technology at the time.
All tig welded. Special caps were inserted, to purge with an inert gas like argon. And special
Clamps to tack in place. With a weld schedule.
Weld shrinkage, heat distortion, and other factors had to be compensated. These welders were very highly trained. Their welds had to have minimum welds, and pass NDT testing. Have simulations for training with actual parts , for testing with your best welders. Take apart the check valves and inspect and record. The weld schedule will be a starting point. Then it has to be adjusted for better results and the the process has to be setup as a fixed process. And can only be changed from who ever is in charged.

 

[Stefan2211]

Some more information. Sizes are 1-1.5" in 316. We finally used a bucket of water since the short pipe spool fit in.

 

[mfgenggear]

Stefan
If this satisfies , and it works. Just be advised. That moisture is not conducive to welding.
It causes porosity. that is why argon was used as a back fil.
But if this a low pressure, and the welds are no concern to pass NDT. Then its good.

 

[MintJulep]

There are various products that claim to do this.

One example.

https://www.muggyweld.com/product/heat-freeze-heat-paste/

I have no experience with this one, or others.

 

[dvd]

for the benefit of the at-home audience -

https://www.checkall.com/product/universal-socket-weld-check-valve-us/

https://www.checkall.com/PDFfiles/installation_guidelines.pdf

I think that a two-piece aluminum shaft collar could be bored to valve o.d. and be a reasonable heat sink. Maybe weld some fins on it if valve gets too hot.

Welding in a water-bath is disturbing.

 

[dvd]

btw - you're showing a flange within a few inches of the valve. Why aren't you using a flanged valve? Ease of maintenance?

https://www.checkall.com/PDFfiles/HV.pdf

 

[Stefan2211]

dvd, Client insist of welding since the media is Monosilane which ignites immediately at ambient atmosphere. Even PITs are welded and need to be cut our once damaged.