Welding on a water cooled manifold???

[Alfaguy435]

Hello Guys

I am looking a project that involves welding super high pressure gas manifolds. They are 2” dia Sch-80 and Sch-160 A-106 seamless pipe with 3000# and 6000# steel fittings. They will have closely spaced (4” O.C.) ½” and ¾” welded outlets. I have seen others weld these before but heat warping was an issue. They are specifically looking to avoid warping caused by welding heat. I will be welding with a standard MIG welder (220V -180 Amp) using multi-passes due to sizes and thicknesses.

I was thinking about hooking up a water hose arraignment to fill and slowly flow water through the manifold during welding to allow for cooling. Then I could drill through the outlets after welding. Any thoughts? Will the water cooled pipe cool too quickly in relationship to the thread-o-lets and cause problems with puddle control and or lack of penetration?

Any help would be appreciated!
Thanks!

[weldgault]

You can use water, but it is better if you don't. If water, you will have to post weld Heat the material to temper the martinsite cause by welding. About 550 Degrees. HAVE RUN WATER IN 4140 PIPE AND DID A LOT OF HEAT TREATING. JOHN

[Alfaguy435]

So if I understand you correctly if I am going to cool with water I should heat the welded area (post weld) to around 550 degrees (F) to relieve stress.

Thanks again!

[Finney]

Alfaguy435,
You say super high pressure gas. How much pressure? We do high pressure pipe daily and run 6010 root & 7018 filler and cap on this type pipe and fittings.
Do you have the proper certs and insurance?

[thingy]

Well,,you could look at this like a welding procedure qualification I guess,,,but you probably already have a procedure,,,but maybe a better word would be a joint mockup,,but than again maybe you just have one to do or so??water through the pipe would cool it and you would think slow down warpage,and might just be the ticket,,maybe,,,maybe another thought would be to preheat it to certain temp by controled means while it was constrianed in someway,weld it,under heat,,,and than run it through a stress relieving cycle,not letting it cool down,,but cooled at a controled rate while still restrained??,,,,asme b31.1 might give you the temps for stress relieving carbon steel,,upper critical temp and all that,,,all maybes,,,the water through it sounds good to me,[if it works],simpliest is always the best,,and I wouldn't really see the need to heat treat it after[if that works],,50 degree preheat is all thats required for 106,no stress unless its over 3/4 thick,[I think],,,so if the water temp was 50 or over,that would meet that requirement,,,air/water,,its about the same,,but codes just say about 50 preheat,,no stress for 106,,,,thingy

[Alfaguy435]

Thanks guys.

The manifolds are for a gaseous fire suppression system. Normally the manifolds are not under any pressure but they are hooked up to several high pressure cylinders filled with inert gas. The cylinder pressures are either 150 bar or 200 bar (2200 psi or 3000 psi). I the event of a fire (or false discharge) all the cylinders dump into the manifold at once.

I am going to try the water cooled thing and maybe try to heat the water to 80 or 90 deg for good measure. I am planned on building a fit-up jig that will clamp manifold in several places during welding. After fabrication I will be hydro-testing at 3000 psi or 6000 psi for one minute.

Thanks again for your comments!