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MIG welding certification tests are kind of rare for structural welding jobs. They are more commonly used for pipe welds.
MIG Weld tests that are given for pipe welder jobs are commonly 6 inch schedule 80 pipe welded in the 6G position (pipe is positioned at a 45 degree angle).
Here is a very common test setup:
- 6 inch carbon steel pipe, schedule 80, 37.5 degree bevel with a 0 "to 1/16" land. 1/8 "gap.
- E70S6 bare wire with 75/25 argon / CO2 shielding gas.
- The root is welded downhill, and the rest of the passes are welded uphill.
Some MIG welding tests use Flux core mig for the fill passes after the root is welded with bare wire MIG. E70S6 is used for the root and E71-T1 is used for the flux core fill passes.
Usually, if the root pass is downhill, its an open butt joint with no backing. If backing is used, an uphill root pass is common.
For open butt root passes, the thing that will kill a test is slipping and shooting wire through the back side. Some test inspectors will fail your test for that … and all it takes is one slip, so being rock steady is key.
A 6G position downhill root pass with no backing requires the welder to continuously reposition his body to keep gun angle and to stay in the sweet spot of the puddle without shooting whiskers through. Sounds easy, but under the pressure of knowing a good paying pipe welding job is at risk, the shakes can take over and ruin your day. That's why its important to practice enough so that you wont be nervous on test day.
- Stickout = the distance between your arc and the contact tip . Keep it short on bare wire mig and longer on flux core
- MIG gun angle. Pipe is round. Duh. right? keeping gun angle correct on 6 inch pipe means changing position smoothly and often. All the while making sure you do not shoot wire through the root.
- Keep the nozzle clean . A nozzle full of spatter will often short out when you touch the copper nozzle to the pipe. It always happens at the worst time. Clean the nozzle every pass.