I am having a problem with 6" X 1\2 " wall thickness pipe ,either cracking or snapping off completely just above the weld. These pipe are used on trench safety boxes, in which pipe crews put in yhe ground while laying pipe to keep the ground from caving in.These pipe are welded to the main frame of the trench box and are used to hold spreader bars in place.They are only 13" long,7" stick out of the box to pin the spreader bars to,I weld them to the main frame at the bottom of the pipe on the inside of the pipe,because you cannot get to the outside it is down inside the frame,at about midway up the pipe where it portrudes through the frame there is good solid 1\2" plate to weld to.I usually make one pass on the bottom and three passes at mid point with 7018 rods.These trench boxes take major abuse with big trackhoes pulling them along in the ground by the spreader bars. I am thinking cheap grade pipe? Itried to heat the pipe, maybe not enough preheat?
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