Arc Welding 101

Preheating a shaft-sprocket assembly

PRACTICAL WELDING TODAY® JANUARY/FEBRUARY 2007

May 8, 2007

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I am building a 400-gallon paint tank and I'm having trouble with leaks when using gas metal arc welding (GMAW).

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I am building a 400-gallon paint tank and I'm having trouble with leaks when using gas metal arc welding (GMAW). I'm using a welding machine running on 440. My best results come when running hot 19.5 on the heat and about 21/2 on wire speed. I am using a trimix gas and 0.035-inch 308 wire. The welds look pretty but are not leakproof. It takes three weeks of 10-hour days to make the paint tanks with GMAW, and it could take twice as long using shielded metal arc welding (SMAW). Any advice or tips are welcome.

"Tank-full" Ted

This sounds like a heck of a project. Here are a few questions: What is the base material type and thickness (type of stainless)? Is it a fillet, edge, or butt joint? What are the wire feed speed (WFS), voltage, and shielding gas flow rate?

It sounds like you are using a fairly common machine, on which that 21/2 on the wire feeder typically equates to 175 to 200 inches per minute (IPM). You should measure the actual WFS output of your machine. To run "hot," use your current 0.035-dia. 308L electrode, and set the weld parameters as follows:
  • A WFS between 500 and 600 IPM should provide 260 to 280 amps.
  • Voltages between 23 and 26 should be measured at the positive and negative studs.
  • Change the shielding gas to 97 percent argon / 3 percent CO2 and run it at 30 to 40 cubic feet per hour (CFH).

These settings will increase weld speed significantly, but you might need some practice to adjust to the speed.

If your base material is thicker than 3/16 inch, then these parameters should work for you, but keep in mind I'm giving this advice without knowing your specific welding requirements. Before you start welding, you should always develop a Procedure Qualification Record (PQR) and Welding Procedure Specification (WPS).



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