HOT (HAZ) what works?

Date 09-17-2013 14:42

Lets say for a pipe that will be under pressure, one is oxy fuel welded with a large HAZ (heat affected zone) and one it zipped up, down hill, or up hill, with any other common electric process.

Now does a pipe that has been heated like in oxy fuel have better resistance to weld or HAZ cracking because the entire joint, plus or minus a few inches to either side of the HAZ, has all been heated together?

Does a small heat affected zone from an electricity based weld provide less uniformity to flexing of that pipe in cases of earthquakes or movement?

Does the Large area of heating help disperse any possible hydrogen that could be in there?

Thanks everyone!

Jordan

By G.S.Crisi (****)

Date 09-17-2013 19:25

The last time I've seen pressure piping (or tubing, in this case) welded by oxyfuel happened exactly 45 years ago, in 1968. They were the superheater tubes of a VU-50 Combustion Engineering boiler in a medium sized (for those days, now it'd be a small sized) power plant in South America.
Are pressure piping and tubing still being welded by oxyfuel?

Giovanni S. Crisi
Sao Paulo - Brazil

PS: Do the words VU-50 Combustion Engineering boiler raise old recalls in someone of you, frequentors of this Forum?

By Milton Gravitt (***)

Date 09-17-2013 21:02

I think if you have a preheat it will take longer to cool down so you won't have no cracks. If you weld it with-out preheat it will cool down to quick and thats where the cracks come in to place, but you should have a WPS to tell you how hot it sould be before and after welding
begans.

M.G.

By MRWeldSoCal (***)

Date 09-17-2013 22:07

Im just talking hypothetical here, nothing with a WPS. Just talking science and Thermodynamics.

Jordan

By MRWeldSoCal (***)

Date 09-17-2013 22:06

Out here in Southern California the GAS company is using a 6" 5G oxy fuel test to get in. Apparently they use oxy fuel for underground piping often.

Jordan

By 357max

Date 09-19-2013 13:57

OAW with a carburizing flame and downhill progression is still used by gas utilities in some areas. Downhill with the filler rod added above the flame/behind the flame. Not adding filler rod in front of flame as usually taught or used.

By Paladin (***)

Date 09-26-2013 12:42

I don't think the local gas company here still use OAW. But those hands that "grew up with it" swore by it on small pipe. One benefit seemed that in a crowded shallow bell hole, one could just lean over with a pair of cutting goggles and zip it up. You don't have a hood on to crowd the hole. And where I would need to lay down to get the bottom the torch hand just bent over. They always used up hill progression, one pass. I would say faster than stick at least on small pipe.

Floyd

By jbndt

Date 09-27-2013 09:36

Wouldn't the type of pipe also have a bearing on the end result?

Cheers,
jb

By Superflux (****)

Date 09-27-2013 16:40

If you're doing a 6" OAW in one pass remember to also use a faceshield (tinted is even better). Your lips will thank you later!
Never got to see anyone else do this process, but did a bunch of refrigeration pipe (4" and under) on a TV Dinner plant years ago. Really is fun after you get the hang of it.