July 18th, 2018
By Dave Lynnes
The final weld on a pipe is called the cover pass. I use 3/32” 7018 electrodes and set the machine around 80 amps. I change my technique from the hot pass and use a Z-weave for the cover pass. Years ago, when I was started welding pipe on the job, I asked six other welders what their cover pass techniques were. All of them had a different technique, and all their welds looked damn good. As a young welder, I realized then that there are several different welding techniques, and how I weld might not be the same as how other welders like to weld.
When starting a new weld, strike the arc 1” ahead of the end of the previous weld, long arc the electrode, and pause on the crater. When I’m using the Z motion, I center the electrode on the edge of the bevel and pause 1001 to fill in any undercut. Then I step up making the Z motion, and center the electrode on the other side of the bevel, pause 1001, move straight across the bevel to the center of the bevel, pause 1001. The slag should chip off very easy if you follow these steps.
If you don’t like how your weld looks, then try stepping up farther, or don’t step up as far, continue changing your technique until you find what works for you. Grind the start of the first weld 1/2” back so can make a nice tie-in to complete your weld.
What I mean by “long arc the electrode” is let’s say our arc length is 1/8” when welding, and we just want to preheat the electrode, we can strike the electrode and lift it 1/2” or so away from the material, and move the electrode to the crater without adding material.