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The ModSquad

hi boo boo
yes ive run into this problem too
when I customized/altered several things on my camper trailer
I used st/st bolts
just before easter this year a tried to undo some of them to replace an item and I finished up twisting the bolts off with a large socket bar and two came undone so far
then luckily i was able to buzz them off with the 4inch cutting disc

i spray them with grease now and it stops the binding
at first I though I must have x-thread them
but that wasn't so
the above thread imfo confirms that there is a problem with st/st material
thanks also for the enlightenment
cheers

the reason this happens is that ss bolts stretch easier than steel.
When a bolt stretches the pitch of the thread changes and the thread "galls", especially if there is a bit of anything hard there such as grinding dust etc.
Once it picks up no amount of force will get it off intact.
Anti sieze helps but SS bolts shouldnt ever be used for load bearing applications. There are high grade SS alloys for this sort of use but for general use, dont use SS.

Usually only a problem when SS threads are an interference fit ie when you are trying to both create a joint and also seal it using threads only. NPT taper and BSP taper are good examples of this. Hence the use of Teflon tape or liquid thread sealer - not only does it fill in the gaps between the threaded components to create the seal, it also provides lubrication between the threads to stop binding. Parallel threads usually don't bind as they are not an interference fit (ie they have a bit of 'slop') and are used to hold the joint together whilst any sealing is done elsewhere eg 'O' ring, crush washer etc
Cheers
TG

Ha ha, tell that to the marine industry!

Me too.
Cheers
Ian

Thanks fellas

Reading through the replies I've learnt a bit more.

Olcoolone, you must be a mind reader! I've just come in from putting a corrosion inhibitor/lubricant on gal fittings for a boat lifter I put on the tinnie a few months ago.

Just a tiny bit of 'green' under the washers.

What you may be referring to is the reaction between two dissimilar metals, galling is similar but it is caused by oxidation of similar metals.

And then you have electrolysis thats different again..... so really you can have three types of corrosion and each is treated differently.

With stainless you can pickle the metal to stop corrosion.

This is one of the reasons you have to have a shield of Argon or a mixture depending on what you are welding to reduce oxidation, aluminium is the worst and will start oxidising with in 5 seconds of being cleaned.

The s/s bolt and zinc loctight nut replacement was bought from a nut and bolt place for $1.40.

gbc,

Not sure I understand your comments re the two grades of stainless steel.
304 grade is the "standard" stainless steel and in some applications requires a coating to stop surface oxidisation. Most commonly used in the food industry and architectural applications.
316 is marine grade and as the name suggests is much more resilient to pitting of the surface.

Not sure there is sich a thing as "standard" stainless steel.
Fact is (and I trained as a metallurgist some few years ago) there are a number of grades of SS, and each is intended for a specific purpose.
The numbers 304 and 316 are simply shorthand identifiers for the particular grade of stainless.
As mentioned, 316 is commonly referred to as "marine" stainless, and this indicates that it is intended for use in environments where it will be subjected to intermittent (or possibly constant) immersion in seawater, or brine.
304 SS is a steel (so mainly iron and carbon) with the addition of 18% Chromium, and 8% Nickel - it is also known as an 18/8 stainless for that reason.
316 SS is a 16/10/2 stainless, being steel with 16% chrome, 10% nickel and 2% moly (hence sometimes referred to as chrome/moly)

Much too much information is available at http://www.assda.asn.au/types-of-stainless-steel for anyone interested in the detail - lists upwards of 70 different stainless steel grades.

Ray

Thankfully the situation I am using the s/s and zinc nut is not critical, ie not a high rust area.

The next time I use s/s I'll use anti freeze or similar.

Stainless steel regardless of grade mixed with zinc or hot dipped galvanize is definitely a no no and it won't take long before electrolysis and corrosion occurs. Never seize and quality marine grade stainless is best answer.