they are not. First of all, an arc strike is not a mark on the steel and/or paint from hot sparks rolling across the steel from welding or cutting operations, even when those sparks are hot enough to develop into “tightly adherent spatter” according to D1.1, 5.30.2. While spatter should be removed per 5.30.2, it is not required to be ground, as an arc strike is, when it has bonded to the base material unless required for ultrasonic testing (UT) or some other application — Fig. 1. Conditions Resulting in Arc Strikes Next, arc strikes are not necessarily close to an area that received welding — Fig. 2. Let’s look at some situations that have resulted in arc strikes. 1) An accidental bump of the trigger on a welding machine with a wire feeder when parts were moved during repositioning for additional work causes a momentary arc that leaves behind an arc strike. It is possible no one even saw it happen, including the welder. 2) The work lead is attached to a skid/horse and a beam placed upon it for fabrication. Upon initiating the arc, the current arcs at the contact between the beam and the skid. Again, it is possible no one even noticed the arc strike and it is nowhere near an 24 Inspection Trends / July 2013 area of welding. 3) A wide flange beam is rolled over on the skids and pinches the electrode lead, which causes an arc blowing out a small area on the corner of the flange and leaving behind a heataffected zone with hard spots. 4) Let’s not forget some other common situations that cause arc strikes, such as accidentally striking an arc with a shielded metal arc welding (SMAW) electrode because the welder did not remove the electrode. While leaving the electrode holder sitting on the work, it flips over and strikes the member. Or, when striking an arc, the electrode sticks, and when the welder yanks it loose, the electrode scoots across the member leaving behind half a dozen arc strikes. Why Are Arc Strikes Ignored? Now that we have identified what an arc strike is and seen some of the conditions that cause them, a question arises. Why do welders, supervisors, inhouse inspectors, and even many third-party inspectors overlook and/or ignore arc strikes (Fig. 3)? My personal opinion, based on many encounters with welders and management, is that lack of training across all levels of welders and inspectors is the major reason for this problem. Training needs to include practical information as to the serious nature of arc strikes. The information from the AWS literature makes it clear that even a “small” arc strike is a potential problem. In fact, a small arc strike can be the worst. Even on members not requiring preheat, a quick arc with a minimal amount of deposited material, because of the shortness of the heat from the arc, will cool so quickly as to leave behind a hard spot with potential cracks. On heavier pieces, this fast cooling is multiplied. A Practical Illustration Following is a description of an experiment I performed after reading about some tests another inspector did on arc strikes. The experiment can be accomplished easily and I encourage you to do it as well. It was very enlightening and the results can be used to demonstrate the severity of this condition to others. I saw a description of this written by John Wright, a fellow CWI, a few years ago, and decided it was something I needed to do myself. It requires a coupon bender, so I built one to D1.1 specs for doing welder qualifications. I then prepared a set of guidelines with some constants. Namely, I ran two pieces of 3⁄8 ×1½ × 6-in. A-36 flat bar through the bender. Both bent perfectly. Next, I ran a couple of coupons through that had been welded as for welder qualifications. Since this was a dependable operator with current qualifications, these also came through with no failures. I now had my baseline proofs. Pretty standard stuff so far. Next, I worked to make arc strikes that would imitate those I have seen in the field. I played with it until I had several using two welding processes, gas shielded flux cored arc welding and SMAW using 7018 electrode. I ran each through the bend test with no repairs of any kind and the obvious happened, they fractured right along the arc strike area — Fig. 4. Since D1.1 requires arc strikes to be ground down and tested, I sanded samples from the first process nice and smooth and tested/bent them. One Fig. 7 — Coupon after welding over the arc strike and grinding it down.
Inspection Trends | Summer 2013
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