[DML] Re: Electrolysis vs Thread Galling

["content22207" <brobertson@xxxxxxxxxxxx>]

You're talking about electrolysis, which is a totally different
phenomenon from galling, though the end result is basically the same
-- a hopelessly stuck fastener.

-Electrolysis IS a problem that develops over time
-Electrolysis IS the result of dissimilar metals in contact with one
another *AND* moisture (just like a car battery)
-Electrolysis IS affected by the environment (will not occur without
moisture)

One major difference between galling and electrolysis: No amount of PB
will help a galled fastener. Only acetylene will.

There's absolutely no threat of electrolysis with stainless on
stainless. There's infinitesimal electrolysis between stainless and
carbon (certainly nothing like the advantage of not rusting together).
Fear of it should not stop someone from using steel studs & nuts, no
matter the alloy.

Electrolysis *IS* a terrible problem between steel and aluminum. Some
people claim that stainless reacts worse than carbon, but I've drilled
out enough Grade 5 bolts to know that it occurs no matter what alloy
is used. Cooling systems are the worst. That's why I've replaced my
bolts with carbon (7mm) and stainless (8mm) studs & stainless nuts.
Studs can stick to the heads and block as much as they want -- when
time comes to work on my cooling system I'll be turning steel on steel.

Best defense against electrolysis on our little engines would have
been helicoils from the factory. Edelbrock's aluminum heads are 100%
helicoiled for that reason.

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, "David Teitelbaum" <jtrealty@xxxx> wrote:
> Galling can be fatigue corrosion too. It is really fretting and
> results from overcycling metal. In threads it can appear because of an
> under-tightened fastener. It can also appear when using dissimialar
> metals in the presence of an electrolyte like water. Very common in
> aircraft which are exposed to weather and high stress loads with a lot
> of cycles. Aircraft also have many different types of metals. This is
> one of the reasons you will see recomended that you use an anti-seize
> compound on the spark plugs. A highly stressed fastener, steel, in
> aluminum. The spark plugs ARE plated to help prevent corrosion but
> that is not enough. Look up the electomotive chart. The farther apart
> 2 elements are the more reactive they will be in contact with each
> other. It has to do with their affinity for trading electrons.
> Electrolytic corrosion is really an electrical plating (or deplating)
> process. Fretting corrosion is a welding process. The 2 pieces of
> metal are brought into intimate contact with heat and pressure and
> separated may times creating the "corrosion" you will see.
> David Teitelbaum
> vin 10757
> 





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