Welding valve ball on the line without demaging the seats - Eng-Tips

I work for a maintenance and automation company.

I'm facing the challenge of finding a way to weld fully welded body Ball Valve.

The matter is that, ones the valve is opened and the seat replaced, the body must be welded again without damaging the seats with high temperature welding.

As it can be seen from the attached pictures, the welding is supposed to be really close to the seats.

Any suggestion/advice is welcome.



... some comments and questions:

you do not mention any size,pressure class, fluid or size, but as seen from the picture it ssems to be a valve of some size and probably a higher pressure class? Depending on details some possible solutions could be suggested,

Some questions are obvious:

How was the sealingsa protected when originally welded into the pipeline?

Possibly other solutions than the obvious 'cooling down'? (other materials, other sealings,mother product within practical and economical limits?)

Dry-ice? (Frozen CO2)



The valve size is from 4" up to 60" and working pressure up to 35o bar.

The seats are made of PTFE, Nylon and even metallic.

The maintenance processes consist of:
-1) cutting valves from the process line in situ
-2) Cutting it as marked in the picture attached.
The presence of soft parts requires particular techniques
that prevent them to be damaged.The same for the ball.
We are investigating how to do it in respect of temperature tollerance, and this is 1st main challenge.
(solution investigated are plasma cutting, or cutting with burr)


-3) substitute seats and damaged components
-4) welding along the same marked lines.
Welding has not to damage soft components. It can be seen from the attached picture that welding will interest "soft areas".
Solution investigated are TIG welding with Argon as cooler
This is the 2nd main challenge.

-5)control and pressure test
-6)welding of the valve in the process line

NOTES:
1) we don't know how was welded previously the valve into the line
Dear Gregorio,
I work in a ball valve company and we produce also fully welded.
For big size of course the problem is not so big as the distance from the welding area to seats is more that enough to prevent any damage.
For small sizes is a more complicete.
Anyway you should ask the company owner of the line to give you the WPS/PQR procedure of the valve manufacturer.
Following them and keeping the welding temperature under control you should not have much problems.
At your disposal for anything further.

Ciao
Thanks to all of you.

One more question:
I would like to investigate more about cutting
It implies to have slag if operated with plasma, laser or oxide acetylene.
Otherwise it can be done by burr, but it takes longer time.
It's understandable that our intention is to prevent at maximum interior parts from damage...

What do you suggest to balance time and integrity ? Replying to Valvit:

After removing the valve from the pipeline we are moving it to our workshop and we are going to cut it by burr and to ovehaul it.

for bcd

After the valve is installed we are going to test it with non destructive method such as radiography.

Thanks again to all for your contribute JohariGregorio,

I have to say, I agree with Valvit. If you need to ask the sort of questions that you are, I would suggest that you're taking on something that you are not prepared for.

I worked for a valve service company where we overhauled Borsig fully welded valves. It is expensive to do properly (over 60% cost of new valves)and in the end we decided to quote new valves and refused to carry out this procedure any more.

When you take on the responsibility of overhauling a valve like this, you are basically offering the client an 'as new' valve. If for any reason the valves fail test after re-build, you have a fully welded valve that you can't exactly strip apart to re-inspect.

Ok, you can stuff the seats full of sealant but each time the valve is cycled the seal may be lost again in this case.

Good luck to you and your company, glad it's you and not me.

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This Piping Valves quiz covers topics related to different types of Valves used in Process Piping. Such as Gate Valve, Globe Valve, Check Valve, Plug valve, Ball Valve, Butterfly Valve, Needle Valve, Pinch Valve, Pressure Relief Valve.

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