Welding stainless questions.

Lets start, I live in the rust/ salt belt. Not sure what Ford uses on their exhaust systems but it has held up pretty well. I have had a problem where the catalytic converter hooks up to the extension pipe. I would MIG with ER70s6. That weld would rust off in 2 years. Not sure if the exhaust is some kind of stainless or ??? Normally I would just keep welding it back up every year or 2.

FYI I am not a pro welder by any means. I do pretty good with MIG on steel. And decent with TIG on steel.

Now today I was working on a flex pipe on my sons car. 07 Ford. The flex pipe was marked stainless, the exhaust is thick and solid. But surface rust. Some stainless does rust. ??? I tried using .024 diameter, 308 stainless wire in the MIG welder and laid a nice bead about 1/4+ long". Then kept getting a birds nest in the mig welder. After that nothing but trouble. I just could not weld for anything. (welding upside down through the frame in a cramped space did not help) The wire would burn back in the tip, stick and birds nest in the machine. Very aggravating. Never have the problem with .030 ER70. (After the MIG problems on son's car I tried TIG. Welding upside down with TIG turned out worse) For future I was thinking of bumping up to .030 stainless. Would that help out with the birds nesting?? Any ideas??? Maybe it was steel not stainless??? Is there an easy way to tell them apart?? How well does stainless filler work on regular steel??

OK, for now... I am going to put a new exhaust on my old truck. Stainless all the way. They do not sell stainless preformed. So I bought a kit. A box of elbows and some straight pipe. I was going to MIG it. (Maybe TIG???) How do you know what wire to get. I was thinking of trying .030. But I am finding 308, 309, and 316. How do I know what alloy to use?? Is one more universal??

Thanks guys!!

OK, From what I have read, Stainless is non magnetic... I will have to take a magnet to it, when he is back over.

It's much more complicated than that though...

Some stainless is magnetic, some is not (remember not only Iron is magnetic, but so is Nickle) and the various "blends" called Stainless (sometimes read STAIN-LESS ;)) can go either way. And Surface Rust isn't at all uncommon, especially on exhaust systems. The MBRP aftermarket system on my F350 certainly has some rust on it but, it's Never going to rust-through! (I think they're 306 and as you go "up", like to 316, that surface rusting disappears. And the price goes "up" too of course).

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Originally Posted by Blaster

It's much more complicated than that though...

Some stainless is magnetic, some is not (remember not only Iron is magnetic, but so is Nickle) and the various "blends" called Stainless (sometimes read STAIN-LESS ;)) can go either way. And Surface Rust isn't at all uncommon, especially on exhaust systems. The MBRP aftermarket system on my F350 certainly has some rust on it but, it's Never going to rust-through! (I think they're 306 and as you go "up", like to 316, that surface rusting disappears. And the price goes "up" too of course).

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Years ago I started off thinking stainless did not rust. Think kitchen sink... Did learn later it did. The OEM exhaust on my truck welded pretty well with ER70S6. But the weld sure rusted off fast over a year or 2. But the pipes just lasted.

Now I am told a shielding gas inside the pipe is needed. OK... I think I will put the exhaust in place. Tack weld it, then take it off and do a good weld off the truck. With what I can.

Nevermind,

You do seem to have stainless MIG filler wire.

OEM exhaust is usually 409 stainless. It turns rusty brown on the surface but lasts a long time unless it gets a lot of salt on it. Many aftermarket exhaust parts are aluminized steel.

309 is a good wire for unknown stainless. It is also good for welding stainless to carbon steel. For TIG pure argon is fine, for MIG you probably want tri-mix or C2.