Puddles we had some outside contractors come into our plant and ground to a nice clean pipe and do some welding on a conveyor or lift table or maybe part of a cross transfer conveyor at the end of two conveyors. The nice clean pipe was electrical conduit.
After the contractors left and production started we had electrical problems half a dozen times per shift with the electrical equipment in the area. No one could track down the exact location of the problem. We lived with the problem until a long weekend or a summer or Christmas shutdown, can't remember which. The electricians went in and completely rewired all the affected equipment. Problem solved.
Clamp the ground close to where you are welding. I know you know this now.
Ever see a welder ground to a rail road track and weld to a box car? He might get more than a a$$ chewing.