After that last post by Ralph, ( If you wanted you can apply a flat patch and put a steel band around it covering the repair. Then don't use it for government jobs. Can't have g-men working with anything that isn't "certified" or up to codes.) I most certainly would agree with him, do what ever you choose with the air tank, my suggestion was merely my opinion. However there must be a reason for the certification tag or stamped numbers on each pressure vessel. Maybe Ralph has just been lucky to not have a bad experience...... yet. Any way something somewhere and some how must have happened that involved some one getting hurt or we wouldn't have a requirement for a pressure vessel to be welded by certified methods and people. Bypassing safety devices and procedures, it's true don't always result in injury, so let me quote Clint Eastwood, "Do you feel lucky punk, well do you"? Keep it away from others what ever you do.