Mild steel studs and stainless nuts?

[Tinbasherdan]

All decent cars used to have "brass" nuts, Always around a nut and a half long.

Merlins use brass nuts too

 

[Kent]

Seriously?
How long is the moisture going to last on an exhaust manifold.

Sure it's a theoretical risk but it wouldn't keep me up at night worrying.
Any sensible person would put them together with a bit of copaslip or the like (no matter what nuts and bolts are used) which would also exclude any moisture.

It has worked well for me.

Obviously long enough to rot the exhausts out

 

[bricol]

I use stainless nuts on my motocross bike which spends most of its life under mud and water and never have a problem removing them from the studs.......

Part of it is due to regularly removing it to maintain it I guess. Cars I was forever modifiying, changing or repairing, nothing seized. Run it with nothing going wrong for ten years and I needed an angle grinder!

 

[Dcal]

Obviously long enough to rot the exhausts out

What I was referring to was for galvanic corrosion to take place an electrolyte must be present.
Whether there is electrolyte present between the threads of a exhaust manifold bolt and nut is what I was questioning.

One of the by-product of the internal combustion cycle is water and there are lots of other products made that will make a good electrolyte so the inside of an exhaust is a perfect environment for creating a galvanic cell, so not somewhere I would recommend putting dissimilar metals.

Little wonder they rot out if not properly designed, specified and made but nothing to do with the discussion or what the OP asked.

 

[Kayos]

I got normal nuts

 

[TechnicAl]

What I was referring to was for galvanic corrosion to take place an electrolyte must be present.
Whether there is electrolyte present between the threads of a exhaust manifold bolt and nut is what I was questioning.

One of the by-product of the internal combustion cycle is water and there are lots of other products made that will make a good electrolyte so the inside of an exhaust is a perfect environment for creating a galvanic cell, so not somewhere I would recommend putting dissimilar metals.

Little wonder they rot out if not properly designed, specified and made but nothing to do with the discussion or what the OP asked.

The galvanic effect occurs when 2 different metals are in contact....so NOT just under the threads....the effect will be present until there is a bridge.

 

[zx9]

I got normal nuts

Sounds like something your avatar would say.

 

[Dcal]

The galvanic effect occurs when 2 different metals are in contact....so NOT just under the threads....the effect will be present until there is a bridge.

Al, what do you mean by bridge?
I fully accept any contact between the different metals can set up the cell and once the circuit is complete, galvanic corrosion will occur.
But you need an electrolyte to complete the circuit. Stainless and mild steel nuts touching in a drawer in the dry won't corrode galvanically.
I've never heard of a dry galvanic cell. (But that means nothing)

In the location we are talking about, any water on the outside of the nut / stud will evaporated pretty instantly when the engine is running and if it's parked up in a damp location (which pretty much covers anywhere in the UK) it could get damp with condensation.
Condensation is by and large de-ionised water which is a very bad electrolyte. I also understand that the condensation will absorb salts from the iron oxides but still not a great electrolyte.
Salt from the roads getting on the nut / stud after the water evaporates off would make a good electrolyte when it dissolves in the condensation after it cools down, but most cars have covers to try and prevent that but it is a valid way a galvanic cell could be set up.

It good to see the OP did the sensible thing and ignored all the advice in the thread.

 

[TechnicAl]

Al, what do you mean by bridge?
I fully accept any contact between the different metals can set up the cell and once the circuit is complete, galvanic corrosion will occur.
But you need an electrolyte to complete the circuit. Stainless and mild steel nuts touching in a drawer in the dry won't corrode galvanically.
I've never heard of a dry galvanic cell. (But that means nothing)

In the location we are talking about, any water on the outside of the nut / stud will evaporated pretty instantly when the engine is running and if it's parked up in a damp location (which pretty much covers anywhere in the UK) it could get damp with condensation.
Condensation is by and large de-ionised water which is a very bad electrolyte. I also understand that the condensation will absorb salts from the iron oxides but still not a great electrolyte.
Salt from the roads getting on the nut / stud after the water evaporates off would make a good electrolyte when it dissolves in the condensation after it cools down, but most cars have covers to try and prevent that but it is a valid way a galvanic cell could be set up.

It good to see the OP did the sensible thing and ignored all the advice in the thread.

When I say bridge I mean a physical end to the piece...a rubber washer or something that disconnects the two metals....thats all

Salt is very corrosive stuff........the standard corrosion test is a salt spray test (the so called G48 test).........

My opinion on this is thst there is enough salt and enough moisture about when the metal isnt hot. When it is hot it will evaporate the water but leave the salt which is primed and ready to do its deadly deed as soon as it moistens.

 

[Pete.]

Road salt and stainless exhaust header fasteners = bad juju. Ask any Suzuki Bandit owner. I've had four and they all had at least one rotted stainless header bolt - one of them all eight snapped like chocolate.

 

[TechnicAl]

Road salt and stainless exhaust header fasteners = bad juju. Ask any Suzuki Bandit owner. I've had four and they all had at least one rotted stainless header bolt - one of them all eight snapped like chocolate.

Salt eats Stainless....Chlorides it is.