Did a side job, didn't go so well

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A guy called and wanted me to weld a 02 bung on his downpipe. I had a few stainless bungs sitting around. He brought me what I thought was going to be a stainless pipe and it wasn't. The magnet stuck to it pretty well. Said the brand was pacesetter. And for some reason it was powder coated. So wire wheel, acetone, and wire brush after I drilled it. Tack welded. Since it was stainless to what I think is mild steel I used 309L, 1/16th. 1.5%, 3/32 lanthanted, 101 amps, 4seconds post flow, 100% argon, 15cfh with gas lens. This is nothing I haven't done a lot, but not sure why i got the results I got.No pics, my phone wasn't with me. Welded halfway around and it came out amazing. Turn the pipe and weld the other half and bah! ****. Did a few dips of filler and got off the pedal to readjust and you can hear the pipe "clinging" and then the cracking began. The half that welded good stayed good, I kept wire brushing and going over the cracks with 309 and same issue. Is it just cheap metal?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Try breaking out your grinder and doing a spark test. It could even be cast iron.My thinking is the inside of the pipe was heavily contaminated with baked-on soot and engine waste products, even prior to powder coating. You heat it up, carbon and gunk gets sucked into the HAZ. Did you drill the hole prior to fitting the the bung on there? If so that might have made the problem worse.You could try getting a couple nickel-based cast iron SMAW electrodes, then breaking the flux off one of them and using as TIG filler Cut the exiting bung off and just start fresh. having one side welded with 309 and the other side welded with a bit of 309 and a bit of nickel isn't what I'd call "quality work."I mean, if I saw any kind of coating on exhaust parts, I'd be skeptical already and tell the guy just what did he think he's clowning around with?  Powder coat has a melting point of.....? certainly well below typical catalytic converter operating temperatures.  Probably the person he paid to coat it just took his money and asked no questions...like that movie "The Transporter."Last edited by Joshfromsaltlake; 08-20-2013 at 11:22 PM.
Reply:I think it was too light to be cast iron. And there was no flange on the back end, so I don't know if it was a slip fit or not. He bought it all powder coated already and was excited because he didn't pay much for it.I really felt bad about how it came out, well at least half of it, so I told him if it ever breaks bring it back and I'll fix it free and told him to pay me less. He was very nice and insisted on paying full price since I did it while he went out to eat.He used a hole saw and started to drill, but didn't get very far. So I used a step bit to finish up the hole.I think powder coating is good for what 400*? Well it won't be on there long as it's was a downpipe connected to a turbo. But then again it could of been ceramic coated too. I don't know a good way to tell the difference between the two.Research is showing me it's 14g aluminized steel.Would mild steel wire on the mig welder of been a better choice?Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Its most likely a Ceramic Coating  and that stuff bonds to the metal its self not just the surface of the metal
Reply:One thing, a wire brush isn't gonna cut powder coating or ceramic coating. This is when I break out a rotary file and get down to metal. Clean clean clean if you want proper results.
Reply:Yep, definitely isn't podwercoat. Could be high temp paint or ceramic. Once I found out it wasn't stainless I would have just migged it.Lincoln precision TIG 275Millermatic 140 MIG
Reply:Thought so. But wasn't sure how well the mig would take to the stainless bung. I guess for next time I'll do so.Do you think the ceramic coating is what caused the hot cracking?No rotary file here  Just a hand file, and wire brush.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer
Reply:Ive welded over HPC ceramic coating before several times with no issues, It just kinda forms a skin over the puddle but once you get through you're good. Didn't seem to effect the weld at all.Welding/Fab Pics: www.UtahWeld.com
Reply:Was it new or used? If it was used then my vote goes to carbon and contaminants from the inside.Lincoln precision TIG 275Millermatic 140 MIG
Reply:It was brand new. No markings on it at all and the end was a slip fit so there was not even any signs of it being crimped.Torchmate 2x2 CNC with Flashcut CNC controlsHypertherm Powermax45 Esab ET220i Razorweld 195 MigRazorweld 200ac/dc TigTormach 770, Tormach xstechRazorweld, Vipercut/Vipermig, SSC Foot Pedal Dealer