Mig welding stainless pipe

GMAW or Mig welding stainless pipe is normally a challenge because of the need to purge the inside of the pipe and because different shielding gases are required than what is used on carbon steel. In this short video a new technology is being used.

Pay attention to the sound of the arc.

That is smooth and sweet.

Stainless steel pipe welds like this are typically fit up using a 1/8” gap +or- 1/32” and each pipe member is beveled to 37.5 degrees plus or minus 2.5 degrees. The sharp edge of the bevel is sometimes filed or ground to about 1/16” usually depending on welder preference

The inside of the pipe is usually purged with argon to prevent oxidation of the weld also known as sugaring or granulation. If the fit up is right and the technique is right, the root pass will look like it has been welded from the inside. It should look like a “wedding band” on the inside.

This machine is using some new technology that is also being implemented by Miller and Lincoln that uses circuitry to control the arc in such a way that the arc is smoother, there is less spatter, sidewall fusion is better, and sometimes purge gas can even be omitted.

WHAT?? I have not seen it yet but I have heard my Miller rep talk about it and I know for a fact that Miller Electric has been working closely with welding instructors from the UA, (united association of pipefitters, steamfitters, and plumbers) to prove out the process.

Eliminating the purge gas from stainless steel pipe joints will make any contractor more competitive and productive because sometimes it takes an hour or more to purge long runs of pipe when joining long piping systems.

Since Argon is heavier than air, it is usually used for the purge gas for stainless steel pipe. All openings are sealed with tape and a hose is inserted with argon flowing. Argon fills the pipe and displaces oxygen.

IT helps to think of argon as water filling up spaces. Thinking about water, there will be Some spaces that will trap bubbles. With argon some spaces will trap air in the same way. That is why there has to be a vent hole at the top most point of whatever is being purged. The vent hole also needs to be large enough that when the weld is completely sealed, pressure does not build and blow a hole in the weld or make is suck back and have too much concavity. Purge dams and purge paper are sometimes used instead of purging a long run of pipe and help cut the time down but some welding codes do not permit purge paper for certain critical applications.


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