Hi everybody, my name is Chris and I'm new here.
I'm learning how to weld stainless tubing to make headers and exhaust for motorcycles. I've been doing a lot of practice with autogenous welding with pulse. I have a lot of practice tubing that's been sitting around for a couple months and noticed almost every weld has this corrosion on the outskirts of the HAZ. I have a Primeweld TIG225X, using a #19 Furick cup with 35-40 CFH and back purging. Prepping with wire wheel and acetone. Also using stainless tubing from multiple vendors. I appreciate any info you guys can give me.
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Last edited by SovereignMotoworks on Wed Jul 24, 2024 12:33 pm, edited 2 times in total.
i'm no to sure on this. i assume your keeping the colors for looks.
normally i get rid of all that with pickling acid, for corrosion resistance. i don't know how exhaust guys keep those colors without it corroding.
A couple of questions: what grade of tubing are you using?
It’s been my experience that if the tubing shows rust after welding, you’ve gotten it a bit hot and have brought up the alloys that will rust. So, as Tweake mentioned, you need to passivate the welds or reduce your heat.
It also appears that your arc length is longer than preferred and the HAZ is spreading out. You could easily drop to a #12 or #16 cup for exhaust tubes. I only opt for a #16 or greater for titanium. And to really get high quality exhaust welds, switch to 321 tubing. It performs much better than 304. If you stick with 304 I’ve seen lots of guys use 309 filler and not have corrosion later if you use any filler.
Yup.. For continued corrosion prevention you want to finish off with a passivation step. Keeping the HAZ as small as possible with a tight arc will also help a lot. LIke mentioned above the problem is that the HAZ has basically drawn or 'boiled off' some of the nickel and chromium from the stainless steel and left a thin layer of plain steel that can rust. So even with good gas coverage it will still rust over time.
Passivation of stainless can, and has traditionally, be done with (harsh) chemicals/acids to etch the exposed plain steel away and bring the nickel and chromium saturated layers back to the top.
But these days you can also use something like https://www.weldbrush.com/ (there's more out there, some even DIY) for a much more 'friendly' method that does not need such dangerous chemicals. (chemical baths/sprays/etc. of course faster and easiest in bigger industrial settings..)
Thank you guys so much. I’m using 304 from multiple venders but will try out the 321. I don’t want to passivate because I and exhaust enthusiasts love those colors. But I do think arc length and heat input is the issue. I’m still new and need some work with my technique. I might need to speed up a little so I don’t overheat the part. I’ll let you guys know how it goes.
Thanks again.
