Qenching/cooling 304L/316L ss pipe welds 1

[Neweld]

We are GTAW (tig welding) 304L/316L SS piping of various diameters and thicknesses in the 1G rotated position. In the smaller diameters (1" through 8&quot we would like to speed up the process with an air/water mist cooling of the weld to an interpass temperature of less than 250ºF. followed by cleaning with a ss power brush. The temperature ranges from about 1300ºF immediately following the weld then falls off rapidly depending on diameter and wall thickness. Are we looking for trouble(s)? If so why?

Thanks...

 

[GRoberts]

Some things you would want to watch out for, is if any water gets near the weld, you could absorb hydrogen, leading to porosity. HIC isn't usually a problem with austenitic sst. Also, with GTAW, the turbulent air could cause sheilding problems, resulting in possible porosity, or oxidized (tinted) welds/base metal with reduced corrosion properties.

 

[bilge]

Microstructurally, you probably won't notice any differance although the HAZ might be somewhat narrower. Hydrogen pickup might be a concern, as has been mentioned, so might a new set of residual stresses.

 

[weld123]

I have been welding stainless steel for about eight years schedule ten, forty, and eighty. When welding anything from four inches and up I have never had a problem with overheating to the point that I have needed forced interpass cooling in order to place the next pass. The smaller diameters yes, but not with the larger diameters. You may already know this but welding thin stainless steel piping takes a special technique all together. The welder has to have a rapid movement around the pipe as he or she welds it. This is acheived using a higher than normal amperage and faster weld travel speeds. And from experince with using water to cool stainless welds it turns them a very unattractive grey and black that is very hard to remove even with a power wire brush. In addition the power wire brush tends to actually move the weld metal and give it an unattractive smeared look. These are just my opinions and experiences with stainless. I would personally slow down and let it air cool and use stainless hand scratch brushes.

 

[Neweld]

G.Roberts, Bilge, Weld 123,

Thanks for your timely replies.

GR, ...no misting during welding, guess I wasn't too clear.

Bilge, McGuire, over in "Piping and Fluid Mech..." said about the same thing.

Weld 123, ...strange how experience notes the same things. We do delay quenching to avoid just the things you mention... the nasty grey stuff and smearing.

Thanks again, Neweld