Ive hasd this happen also on mild steel (carbon). It has alot to with little air pockets in the molding process. Cheap forging basically. I had a air pocket and a piece of metal popped out and of all the places to go it decided to travel down my back. I dont think ive ever got a shirt off that fast in my life lol
It's happened to me but it wasn't bad steel it was drops of sweat comming out of the band in my helmet. It happened a couple of times before I figured it out. I got one of those nice sheepskin liners and that fixed it.
Really, this is true.. When I'd do my last fitup check with the the helmet on and up the sweat from my forehead dripped into the joint and I didn't see it. I guess when the heat hit it, the hydrogen and oxygen parted ways and it popped and blew a hole in my weld. It happend a couple of times and was really making me mad and then I saw it.
Now that's not to say this is your problem but it could be moisture or oil comming to the surface so try preheating it with a map gas torch. Can't hurt and might just solve the problem.
Really, this is true.. When I'd do my last fitup check with the the helmet on and up the sweat from my forehead dripped into the joint and I didn't see it. I guess when the heat hit it, the hydrogen and oxygen parted ways and it popped and blew a hole in my weld. It happend a couple of times and was really making me mad and then I saw it.
Now that's not to say this is your problem but it could be moisture or oil comming to the surface so try preheating it with a map gas torch. Can't hurt and might just solve the problem.
Highly skilled at turning expensive pieces of metal into useless but recyclable crap..