DR wrote:
Mike Spera wrote:

I always wondered why we use plain steel studs and nuts for this
application anyway. It screams "corrosion". Why not heli-coil the port
threads and use a stainless bolt and lock-washer? That way, the
threads are protected from the elements to some degree and using
stainless hardware gives you a little better resistance to rot.

Any engineers know why studs are used on exhaust systems in general?

Thanks,
Mike


It is not true that SS is superior to other steels for all corrosion
issues. When you realize that SS has to be in contact with oxygen for
it's corrosion resistant layer to be maintained, you start to appreciate
why corrosion can be a big big problem (especially in sealed threads or
places where acids can form...)

I wonder why all the stainless fasteners in my airplane last for tens of
years without corroding solid at the threads while plain steel lasts a
fraction of that time and rusts solid? Any ideas why?

-see http://www.corrosion-doctors.org/

Add some electrical current and/or salt and you may have a very big
problem when using dissimilar metals... Bottom line: Keep similar metals
together if at all possible and if you can't, make sure you know which
one will corrode and which can be easily replaced. A mild steel stud can
be cut, have flats filed into it or even be drilled out to effect a
perfect repair. No so easy in SS (especially when the stud eats the
metal it's screwed into)!


Well, you already have dissimilar metals. The head is an aluminum alloy
and the studs are steel. As for removal, stainless requires a lot slower
cutting speed. Most folks ignore this and blaze away with a HS steel
bit. The bit dulls in seconds and the person doing the drilling thinks
stainless is "harder" cuz it takes a long time to drill anything with a
dull bit.

Thanks for the feedback. I'm still wondering if this is really all about
the money and plain steel hardware is cheaper and thus desirable from
the engine maker's point of view. I don't recall ever seeing SS exhaust
studs on the market. As you pointed out, there may be good reason why
they are not used. On the other hand, if the reason is that someone is
trying to save a few pennies by using plain steel, that would be a shame.

my 2c

Cheers MarkC