Back Purging Stainless with Argon
On full penetration welds the penetration side should also be shielded with argon.
Certain applications like filling mis-drilled or worn out holes in stainless sheet metal allow for copper or aluminum backing but argon shielding is often superior to backing.
When molten stainless is exposed to the atmosphere a condition known as granulation aka sugaring occurs. This is not the same thing as carbide precipitation but its not good because it weakens the weld and also provides crevices for bacteria to grow.
The best way to prevent sugaring on the inside of a pipe or tubing weld is with an argon purge.
A Dual Flowmeter is a convenient way to get purge gas without needing an additional cylinder of argon.
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8 rules of the road for TIG Welding Stainless
- Heat builds up in stainless steel due to low heat conductivity and once heat builds up, it is hard to outrun.
- 3 Second rule...get the puddle established and moving within 3 seconds…2 seconds is even better
- Travel speed is one of the biggest factors when it comes to overall heat input...a slow travel speed with low amps can often overheat stainless more than a higher amperage with faster travel speed.
- Heat sinks in the way of fixturing or chill bars can help a lot to remove heat from stainless and prevent heat from building up.
- A gas lens setup helps. TIG cups like the Jazzy10 make a big difference and help prevent discoloration
- keep the hot tip of the filler rod shielded in the argon and snip the end between restarts if the tip gets discolored.
- purge the back side with argon on full penetration welds...when not possible, often copper or aluminum backing can help trap argon from the torch and provides adequate results.
- Use only stainless steel wire brushes that have only been used on stainless (a good practice is to label and keep your stainless brushes stored separately from carbon brushes.)
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