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recommendation for anti-seize?

recommendation for anti-seize?

(OP)
I am designing a pressure vessel that will be using Inconel 718 bolts due its strength retention at the design operating temperature of 550C. Preliminary testing has shown a problem with galling when torquing the bolts with dry threads, so I am considering using anti-seize to prevent galling.

I did a search on anti-seize in the forum and came across a statement that using the wrong kind of anti-seize can be disastrous. No specifics were offered, but I gathered that the problem lies with the anti-seize compound "baking" at high temperature and becoming a solid, like epoxy maybe.

So is that simply a problem with using anti-seize that is not rated for the temperature, or is there more to it than that?

Any recommendations? As I said, the operating temp is 550 C, the bolt material is Inconel 718, and the bolts are 1-8 UNC and will be preloaded to 31,000 lbs each for the hydrotest, and 20,000 lbs for design temperature and pressure.

Thank you.

RE: recommendation for anti-seize?

You could try the types of copper/silver anti-seize that the auto parts stores sell for exhaust manifold studs. This stuff does cook at high temperatures, boiling away the solvents/oils, but does offer some degree of barrier protection against metal/metal contact and diffusion bonding/galling. The gunk left behind helps hold the soft metal particles in place and maintain the barrier. For high temperature vacuum service (risk of diffusion bonding or solid state welding, e.g. vacuum braze furnace tools), we would always use boron nitride spray, BUT this will tend to flake off and disappear if it gets a lot of vibration and exposure to moisture; you may want to test it.

RE: recommendation for anti-seize?

I wouldn't be looking in auto parts stores for something like this.
I-718 is used for critical nuclear bolting, so I'm sure EPRI has something to say on the matter; try searching there.
https://www.epri.com/

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: recommendation for anti-seize?

The silver containing ones are what you are looking for. And yes there are high performance versions that are free of halides and any low melting point materials.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: recommendation for anti-seize?

You want Nickel anti-seize for elevated temperature PV bolting applications.

RE: recommendation for anti-seize?

If you'd believe it, milk of magnesia (unflavored) does a great job of stopping stainless from galling, and can take quite a bit of heat as well, suspect it would work similarly on inco.


I actually have a bucket of 718 bolts in my office that were all lubed with nickel, and exposed to temps <400 F. Almost every one of them had to be cut. I really ought to throw those out...

Nathan Brink

RE: recommendation for anti-seize?

Not going to name any names, but a common well known 100% nickel antiseize.


I've just had terrible luck with nickel antiseize in general. I'm all about moly disulphide lubes myself, but that's a little toasty...

Nathan Brink

RE: recommendation for anti-seize?

Magnesium oxide (milk of magnesia, dried) works ok, but it hardly sticks to most iron/nickel alloys at all. We had better luck with BN powder or spray. Again, both of these are typically applied without any binder (grease/oil - things that boil off in vacuo and contaminate test cells/pumps) and so tend to flake off with very minor handling/vibrations.

Nickel antiseize on nickel alloy bolting does not compute, but if metengr says to try it, I'd test it.

There are some versions with lead and lead oxides that were used historically; you can still find the stuff in industrial supply catalogs.

Oh and yeah, don't trust automotive engineers when it comes to PVs, what do they know, just building millions of very high temperature, million-cycle loaded pressure vessels operated by amateurs in every environment known to man. MY personal experience with Inco 718 bolting doesn't come from nuke plants, it comes from rocket and jet engines and their associated R+D, so by all means ignore my silly ideas. FWIW, OP you mentioned testing and I think that is the wisest thing said in this whole thread.

RE: recommendation for anti-seize?

I have used MgO in the lab, but not sure that I would want to rely on it for long term applications.
Spray can BN is even better, but it is also soft and the coating is fragile. It is very slick though.
We also used it in the lab. But we had a good control over cleanliness and application.

For long term high temp stuff we used to favor solver platting the bolts.
We would use them up to 1550F (850C), and it is reusable.
Avoid anything with lead, tin, sulfur, cadmium, zinc or any other low melting point element.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

RE: recommendation for anti-seize?

Any compound you use will act as a lubricant and you will need to confirm the relationship between torque and bolt stress; i.e. coefficient of friction. Given the high operating temperature that is a tricky proposition.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

RE: recommendation for anti-seize?

I've used copper anti slip agents on Inconel 718 bolts upto 850°C, but also in a lab environment. I had no issues and from memory opened up easily after the heat cycle.

RE: recommendation for anti-seize?

Not torque. Not lubricant. Use hydraulic tensioner.

Regards
r6155

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