Stainless steel nuts galling on stainless steel bolts

Never-Seeze, or a similar anti-seize compound. Or Loctite - depends on how easily you want them to come apart, .vs. stay put. Axle grease in a pinch, but anti-seize is better.

Per Ecnerwal:

If you talk to folks who assemble stainless vacuum systems, they'll tell you that the quickest way to having a nut permanently installed on a bolt is to assemble them dry, and then bake above 100C.

You have to cut them apart. The answer is just put some molykote on them before assembly. The nickle and copper based anti-sieze compounds work too. Doesn't take much.

Jim

Commercial solution, that for example Swagelok uses in their SS parts, is to silver-coat the thread of one part - usually nut. Works really well.

The brute-force solution is to use anti-seize grease on the thread. Propably what you should do - I use Omega 99, but any such compound is ok. In places where graphite (or other stuff that makes a mess - most of these make a mess) is a no-no, high-vacuum silicone grease works ok.

I know the hard way that clean SS surfaces of nut and bolt can seize even at room tempeture when installing them together, BEFORE even really tightening. That happened with parts that I had just cleaned of any grease in hot acetone in ultrasonic cleaner - if memory serves, it was M8 fine thread in aisi 316L. The way to open them is to turn the nut while hammering it - it will open a little bit each time hammer hits it from top. I've seen people do this to BIG nuts when they've forgotten to use the anti-seize compound and the parts have been to 300+ C.. It takes a large hammer (BFH) and long wrench to open. :)

Kristian Ukkonen.

spaco wrote in news:hoydnTYZZKveqKTZnZ2dnUVZ snipped-for-privacy@bright.net:

The answer is here:

"spaco" wrote in message news:hoydnTYZZKveqKTZnZ2dnUVZ snipped-for-privacy@bright.net...

Try wrapping the thread with Teflon plumbers tape before you screw it in. There is a compound that you can buy with Teflon in it that is brushed on but I can't remember the brand name. Teflon tape can be found at most hardware shops.

Tom

stainless on stainless mthreaded fasteners should be put together with a quality antisieze [ spelling ]

never with out , unless you want a semipermanent installation

Hardware and plumbing supply stores sell teflon-loaded pipe thread sealant. Is this what you mean?

Joe Gwinn

As other's have said, a good anti-seize compound. Most stainless materials gall at very close to 2000 PSI...this includes 17-4 and 17-7 precipitation hardened parts. It doesn't take much pressure to hit that

2000 psi level on fasteners considering the ramp-action of the threads as well as the relatively small contact area.

Anyway..just wanted to throw out that 2000 PSI number as food for thought in the group. If you calculate backwards based on bearing area and torque on the nuts, you'll see how little torque it takes to gall out a stainless bolt/nut. If it gets really critcal and you have deep pockets, Nitronic 60 stainless is available at about $ 12.00 per pound (at least that's what it used to be). Nitronic 60 doesn't gall until you get to about 50,000 PSI and is used on bridge pins and critical stuff like that where galling could really muck up the works.

Koz

SS bolts with brass nuts, or use copper or silver bearing anti-seize. I like the brass nuts on stainless bolts.

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Hamilton-Standard used to specify a molybdenum-disulfide dry film lubricant (Electrofilm 100 if I recall correctly but it's been a couple of decades) for the bolts holding the afterbody housing on the 54H60 propeller together (this is the prop on the C-130, P-3, and Electra) to deal with just such a problem. Worked pretty well--they were 3/8" flat heads assembled and disassembled with an Allen wrench and the Allen usually got them out.

Yep - SS on SS is bad. What happens is you get intramolecular welding between the two parts. The solution (if you MUST do SS on SS) is to "contaminate" the surfaces. As said earlier, silver plating works best, but any contamination will help. Anything with moly-disufide is good: grease, anti-sieze compound, dry film lube, what ever. The best contaminate is baked or otherwise adhered to at least one of the surfaces, soft, and thin (so as to not fill the threads). Good luck.

If you look closely under a microscope at a siezes part like that, you see that the material welds up, then tears free as it begins to try to slide - with the result being tiny 'snowballs' of metal that grow larger as the sliding continues. Eventually the rolled up metal is large enough to cam up inside the thread clearance, and the fastener jams.

This is one reason why, if you suspect a fastener is just beginning to sieze up as you loosen it, you should immediately snug it back down and try to get some penetrating oil into it by capilary action. Soak it, tighten, loosen in repetitive cycles.

At some point there will be enough oil in there to prevent the continued weld-up of additional metal to the ball that is trying to grow in there.

Jim