Stainless Steel Welding

There is a lot of discussion re: discoloration of weld joints where unclean gases are used. Obviously a purge gas keeps a positive pressure so to create a smooth joint but it also keeps contaminates out of the joint as well.

Typical orbital welding of high-purity systems employs GTAW (gas tungsten arc welding) for its cleanliness, repeatibility and speed using either five nine Ar or N from a purified source and a point of use filter.

I have been through countless meetings and evaluation sessions as to how these impurities effect product integrity. No one has ever come out and said "OK, this is the chemical makeup of the halo, or yellowing at the joint".

Please tell me what you are piping (product) and what your welding equipment is and I may be able to elaborate.

cr3

I guess a point worth noting is use of INERT gas. It is nonreactive, nonflammable and noncorrosive.

We wouldn't want to try and weld with silane or oxygen as a purge gas, now would we?

cr3

If you have no gas available, Why not use self sheilding process like SMAW?

The purpose of the gas is to keep hydrogen and oxygen out of the joint. Chrome in stainless is to pick up carbon to keep it corrosion resistant. Oxygen can form with many elements with higher bonding affinity contaminating the weld with porosity etc.

Hydrogen will embrittle the joint through atomic to molecular change upon cooling.

Use argon as your shielding gas.

No gas - big problem

If you do not have access to gas then use chromium/stainless welding rods that generate their own gases to shield the weld.

Tig is cleanest method though

argon is not required. It depends on how clean you want the joint.

For welding e.p. or b.a. tube GTAW is the preffered/required method for mainting system integrity. And, five nine Ar internal & head purges are required.

Parameters such as

.1micron particles<10 ppb

trace gas analysis at a low ppt level

helium leak at <10E ^-9

I like using a tri-mix .... CO2-Argon and a touch of helium.

Hi Guest,

Please tell us the kind of weld: ARC or MIG or MAG. And the size with thickness of stainless steel pipe was welded.

best regard