Hi! This is my first post. I asked a friend of mine to TIG weld a SS coupling to a keg (used as a HLT) so that it's sits flush with the inside. That's what he did but I figure he had a hard time because now some of the threads inside the coupling have been damaged with slag. I can't screw in my 1/2'' male fitting to hook up my pick up tube. Any ideas on how to clean up the threads so I can properly screw in my fitting?
You may be able to reach through with a long skinny screwdriver and knock the slag off the threads. Slag may or may not be stuck hard. If that don't work you may need to buy a pipe thread tap and use it to chase the threads.
It sounds like to me that the coupling cooled down and became undersized not allowing you to thread your fitting into it on the inside. Get a new or a sharp tap with lubricant and chase the threads you'll be surprised how much the coupling has shrunk down after it was welded in and cooled off. Your not the first person to have this problem. I bet it was a tight fit thru the keg before the welding began as this will increase the shrinkage of the fitting also.