Stainless steel pipe welding is heavy work. Always has been. It will always be.
If you can do it and do it well, you are the man and you will never go hungry. But it takes some attention to detail to get it right.
The main thing that separates the men from the boys or should I say, true stick burner welders is a willingness to follow procedures for welding stainless steel. Procedures such as waiting for the pipe to cool down between passes, keeping the hot rod tip shielded with argon, cutting off the TIG welding rod tip when damaged, keeping the tungsten sharp.
One of the main procedures I am talking about is the PURGE. It is absolutely necessary to purge stainless steel with argon gas to prevent sugar formation. Sugaring is also called granulating, but it’s severe oxidation no matter what you call it.
You can’t even get away with spot welding without an argon purge protecting the back or inside of the pipe. So how do you do it? How is the rear protected with argon?
It is usually done with aluminum foil tape. The ends of a stainless steel tube are taped shut and the entire interior purged with argon gas. Even the opening in the pipe joint is perforated so that the argon can fill the entire pipe and expel the oxygen. The tape is removed enough to get a tack once the pipe has been sufficiently purged.
What is enough? The only way to know for sure is with an oxygen analyzer. A bic lighter will not work. Even 2% oxygen content will put out a bic lighter. And 2% oxygen will result in a black root pass.
There are other dirty and dirty ways to check purge, but an oxygen analyzer is the sure way.
Here are some tips to help you get a good purge on the stainless steel pipe you weld.
- Make sure there is no water inside the pipe…not even a drop. A single drop of water will throw a wrench into your purge until it evaporates. Do you remember what’s in the water? Hydrogen and oxygen.
- Make a ventilation hole in the highest place you can find. Think of argon as water. Because it is heavier than air, it will fill any space like water, displacing air as it fills every nook and cranny.
- More purge gas flow is not always better. A high, turbulent flow of argon will not necessarily purge a pipe faster than a lower flow rate. And a diffuser at the end of the argon hose usually allows you to use a higher flow rate. A homemade diffuser can be made with some stainless steel wool, some perforated stainless steel sheet metal, and some sheet metal.
Once you verify a good purge, you are ready to turn. Peel off the tape enough to stick and let it cool down a bit and stick again. Then turn again with a separation of 180 degrees. Continue until all the tacks are in place.
More tips for welding stainless steel pipe…
- Placing a 1/8-inch wire into the root works better than dipping a 3/32-inch rod.
- Use a feather edge bevel. no land needed
- You can fix the areas that do not penetrate by resoldering
- Only use stainless steel wire brushes and only use files that have only been used on stainless steel.
- Use only enough amperage. Using too much amperage will overheat the stainless steel and cause things to go bad quickly.