I worked at bicycle company for the longest time, and no matter how careful and caring we were, we'd have our share of defects each and every year. I am sure a reputable company like the one you are working with will do everything they can to make you happy if you give them a call - maybe an earfull too!
My guess is that they will offer to have you ship the pipe back and that they will weld it and pressure test it for you. You might even have luck asking them to repaint it and heat cure the finish since they caused you some grief. Don't be too hard on them though, we all benefit from vintage specialty companies making it possible for us to keep the bikes going strong. Good luck!
Jon