Welding bods – can I weld stainless steel to steel? (exhaust)

I’ve got a mig welder setup gasless at the moment… as I’m using a mates and he doesn’t have gas!… I’ve got to fix my exhaust flexi pipes and the replacements are all stainless steel… what do I need to do differently to weld them to a normal steel exhaust pipe or can I just carry on as normal?

I’ve got a feeling there was some wire that worked better for this application but didn’t know if it was needed or not?

Thanks!

You want 309L filler, as per this, however I’m not sure if you can get that in a gasless combination.

Cheers, Rich

I have MIG welded stainless to mild steel on an exhaust before with no issues

You can do it the same, the weld with go rusty but so is he mild steel exhaust. You would get better results with gas instead of flux core

i was thinking of painting it with hi temp exhaust paint to try to prevent the rust .. my mate doesnt have a regulator or anything so was hoping to get away with normal gasless mild steel wire… shockingly horrible bodge or real world practical?

There is nothing inherently wrong with welding Mild steel to Stainless – we’ve built pressure vessels for Naval Ships using this technique.

They’ve been TIG welded though.

Paint the mild steel, weld and the stainless section to reduce the possibility of galvanic corrosion.

There is nothing inherently wrong with welding Mild steel to Stainless – we’ve built pressure vessels for Naval Ships using this technique.

fingers crossed the design allowed for the around 50% difference in the coefficient of linear expansion between mild steel and austenitic stainless steels

same with the exhaust pipe the differential expansion can potentially tear the weld apart depending on which material is most constrained

I will just repeat what was said above. You need 309 wire. If you have no gas, then the wire will need to be self shielded flux cored. If it is solid wire then you’ll need Ar gas.

As for using mild steel wire. That’s a tricky one. I’ve never tried as I’d get the sack for trying something so reckless on a subsea pipeline. However, in theory it would possibly do the trick (I.e. the pipes will stick together). The weld will be very brittle though, but I’m not sure whether that is important for your application. Give it a go and let me know how it pans out – I’m always interested to know if the stuff they taught as at the Welding Institute is actually true!

Yeah i’ll go for 309 … dont want to risk it really if it falls off it’ll be a mess! it doesn’t look like you can get gasless 309 though doh!!!

Looks like I’ll have to wait to get my welder back

There is gasless 309 wire (ESAB do some here), but suspect it’s a bit too niche to find in a normal shop. It doesn’t have to be 309 by the way – there is a myriad of other options, but 309 is the stock answer. If you can find any other gasless stainless steel wire then let me know and I’ll tell you if it’ll be ok.