304 stainless exhaust question

admin

A customer brought me a motorcycle exhaust that has a dent rite on the outside bend that he wants filled in. I have been welding on some of the exhaust pieces he makes for the last couple months without too many issues but this one bugs me. The problem I'm having is as soon as I light up on it the material starts to sink before I can even get the puddle started. The material by my gage is 0.068. I'm running a 1978 dialarc HF at about 45 amps with 11 cfh argon. It welds out fine I just can't prevent the sinking.Thank you in advance for advice or direction. Sent from my iPhone using Tapatalk
Reply:purged?
Reply:Have you tried filling it with air (probably 10-20 psi) and slowly heating the bent area until it is uniform again? I would try this before welding it but I don't know what the damaged spot looks like! I've had good luck running about 25-30 amps on harley exhaust tubes when I've got to butt weld them without overheating the pipe. Just remember you will most likely need to run very short beads if your filling a dent in thin wall material to keep from overheating the area..You could always weld it upside down! Then the dent will (sink) outward!!Real welders know how to penetrate!(Equipment)Whatever can be used to beat my opponent into submission!
Reply:Originally Posted by traumajunkie720A customer brought me a motorcycle exhaust that has a dent rite on the outside bend that he wants filled in. I have been welding on some of the exhaust pieces he makes for the last couple months without too many issues but this one bugs me. The problem I'm having is as soon as I light up on it the material starts to sink before I can even get the puddle started. The material by my gage is 0.068. I'm running a 1978 dialarc HF at about 45 amps with 11 cfh argon. It welds out fine I just can't prevent the sinking.Thank you in advance for advice or direction. Sent from my iPhone using Tapatalk
Reply:Not purged and thought that could be a issue. But it is a pipe inside a pipe and he has the inside pipe wrapped in the exhaust tape. I did try welding it overhead and gravity was not my friend. It still sank the wrong direction. Have run small beads and let cool to ambient before running another run. I'm at the lowest amperage I can be and still get a puddle. Sent from my iPhone using Tapatalk
Reply:"Its called thermal expansion. As sheet grows, it always will move towards the side it is convex on, simple geometry. Part of welding is understanding this."Makoman1860,Thanks for the teaching moment we all are not perfect or we wouldn't be on this site. Please enlighten me more as to why the metal is NOT moving toward the convex side as you explain it will do? Sent from my iPhone using Tapatalk
Reply:Originally Posted by traumajunkie720"Its called thermal expansion. As sheet grows, it always will move towards the side it is convex on, simple geometry. Part of welding is understanding this."Makoman1860,Thanks for the teaching moment we all are not perfect or we wouldn't be on this site. Please enlighten me more as to why the metal is NOT moving toward the convex side as you explain it will do? Sent from my iPhone using Tapatalk
Reply:Ok I get what you are saying in that respect. The dent is on the convex of the pipe where it was bent and that is where our communication got crossed. I live in a small town with only two other welding shops and they know nothing of stainless or any of the properties. I did make a call to the collage instructor and he advised I might be running too small of filler. I also talked to the customer and laid out the options. He requested I fill in the dent with filler and he will file/sand as he does not want air blown in and the way he explained how the "pipe in a pipe" is mounted there doesn't seem much of a chance the full pressure would reach the area of the dent. He has several rings through that would block airflow and they are hammered in to hold the inside pipe tight. Thank you all for your help! I will just fill it and roll on. Sent from my iPhone using Tapatalk
Reply:Originally Posted by traumajunkie720Ok I get what you are saying in that respect. The dent is on the convex of the pipe where it was bent and that is where our communication got crossed. I live in a small town with only two other welding shops and they know nothing of stainless or any of the properties. I did make a call to the collage instructor and he advised I might be running too small of filler. I also talked to the customer and laid out the options. He requested I fill in the dent with filler and he will file/sand as he does not want air blown in and the way he explained how the "pipe in a pipe" is mounted there doesn't seem much of a chance the full pressure would reach the area of the dent. He has several rings through that would block airflow and they are hammered in to hold the inside pipe tight. Thank you all for your help! I will just fill it and roll on. Sent from my iPhone using Tapatalk
Reply:You would be correct about cutting it out and reshaping and weld it back in but the pipe in the pipe becomes a factor and the exhaust wrap inside doesn't help. Then there would be more to sand and polish. So it's all filled in and a rough grind done on it. Now the customer can finish sand and polish it. Providing he doesn't drop it again it will be shipped to it's new owner on Friday. Sent from my iPhone using Tapatalk
Reply:Most motorcycle shops around me clamp rubber stoppers in the end, heat the dent until red hot , and gently pressurize until dent comes out.Weld like a "WELDOR", not a wel-"DERR" MillerDynasty700DX,Dynasty350DX4ea,Dynasty200DX,Li  ncolnSW200-2ea.,MillerMatic350P,MillerMatic200w/spoolgun,MKCobraMig260,Lincoln SP-170T,PlasmaCam/Hypertherm1250,HFProTig2ea,MigMax1ea.
Reply:Originally Posted by shovelonMost motorcycle shops around me clamp rubber stoppers in the end, heat the dent until red hot , and gently pressurize until dent comes out.
Reply:Hello,I have dealt with issues like this before.  One repair included a similar repair as yours, except there was an actual small crack at the bottom center of the dent.  I purged the inside, and used a manometer to adjust and maintain the inside pressure while providing a purge.  The setting of the internal pressure is key to have the dent push out slowly while still fixing the crack.  My experiences with orbital welding lent to this solution.  Another similar repair, was to tac a small screw to the center of the dent and use a small slide hammer to pull the dent.  I didn't drill a hole  and turn the screw in because I wanted to avoid welding the hole back up.  Took several pulls at different locations, but once re-polished it looked great.  Good Luck.