Trick for magnetic material
Lets say your burning 5p+ on a cattle guard. All the sudden the arc puddle explodes and your going WTF? Your thinking somebody is messing with me, right, but you look around and no ones around. Well take your stinger lead and wrap around the pipe as close to the area where you are welding(4or 5 wraps should do) and get on with the job. About 80% of the time it will allow you to get a good arc-puddle and heat up the area and get rid of the magnetism.