I know might be making more out of this than it needs to be, but I was having a conversation with one of our material experts the other day about welding dissimilar metals (SS to carbron steel, titanium to SS etc) and a lightbulb went off in my head.

Many of us use titanium test pipes with stainless exhausts and those are obviously joined in some fashion. Has anyone ever heard of a corrosive reaction triggered by the chemistry of the metals? What kind of hardware would you use to join the two? SS, Ti, zinc?

Crazy, I know...but humor me

 

bump

 

it's (galvanic corrosion) not enough to worry about. If you use zinc to fasten the two together, that'll be the first thing that corrodes. But unless you're driving a lot on salty/wet roads, you won't have any issues.

Just use stainless fasteners and call it a day.

 

Well, if you have a Ti testpipe and SS downpipe, there should be a gasket in between them. Usually gasket material is some type of composite.

Also, I would stay clear of SS fasteners on exhaust components. SS fasteners are not ideal for high temp applications as they will gall.

 

Post turbo they should be fine.

plus your mounting hardware will set up a conductive path between the dissimilar metals, the gasket won't be enough by itself.

 

I used SS hardware on my old GSX at the cat and they galled. I had to cut them off to get them out. A test pipe should generate less heat, so it may be okay. But you'd still be riding the edge of them galling, so why risk it.

 

yes, cats get very, very hot and could very well pose a problem for stainless. I've had trouble with carbon steel bolts on cats, but never had issues with stainless on test pipes where it connects to the dp or catback. It's a matter of picking the lesser of two evils, galling or rusting. Both can lead to having to cut the bolt or strip the crap out of it till you can muscle it off. Carbon stell will be the anode compared to stainless, so that will make them rust even faster than normal.

 

...hmmm...and here I was thinking that I am the only one that ponders such issues. From what I understand by people's comments there is no "safe" solution and one has to choose something, one way or another. I think SS fastners are the way to go, understanding of course that they present certain limitations like any other solution (carbon steel, zinc etc).

Good stuff people, we have some serious scientists on here, hehehe.

 

the reason stainless steel gall/cold weld is because it is too squeeky clean. A very light coat of lithium grease, moly disulphide, copper/nickel anti seize will prevent that. WD40 is too light, gets washed out or evaporates with heat.

 

Yeah, I think there are threading compounds that prevent galling. Put that on and you are good to go. SS rocks.

 

Isn't it called formicary corrosion?

 

this kind of corrosion occurs in copper, very localized, causing the formation of pinholes. happens in refrigeration tubing causing freon leaks

 

i know, lets all ask Bill Nye the science Guy!!