Anti seize compound 1

[rQuestionEngineering]

1. Why stainless steel fasteners required nickel free anti seize ?
2. Is copper based anti seize compatible with stainless steel fasteners ?
3. From the Molykote series/brand , what is the best product for stainless steel fasteners on 316L piping (ASME B31.3) ?

 

[EdStainless]

1. Beats me, I have used it.
2. under most conditions yes. I severe corrosion environments I wouldn't use it.
3. I have found that one MoS2 is about the same as another. I actually prefer h-BN (hex boron nitride)

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P.E. Metallurgy, Plymouth Tube

 

[MintJulep]

Nickel anti seize is recommend for stainless in most conditions.

Why do you believe the opposite?

However, nickel is a likely carcinogen.

https://www.cancer.gov/about-cancer/causes-prevention/risk/substances/nickel

 

[moltenmetal]

Nickel powder is a possible respiratory carcinogen, as is nickel oxide, so it would be a concern after you'd heated the fasteners to the point that all the grease and binder were gone- but nothing that a dust mask wouldn't deal with, which you'll likely be wearing because of the insulation involved in lines which get that hot. So the issue isn't with the compound itself, but with what you get after it has been cooked for a long time.

Anti-seize compounds are recommended and sometimes necessary to prevent galling in same-on-same stainless fasteners even at room temperature- I've seen cheap 18-8 nuts and bolts seize at room temperature when used dry at torques necessary to develop full strength in the bolted joint. If you want to disassemble a threaded stainless steel component after use at high temperature, antiseize is a practical necessity. Less of a problem if the grades of material used for studs and nuts are different, if the threads are rolled rather than screw cut or die cut etc.

 

[EdStainless]

On Ni alloys I like using a Ag bearing anti-seize.
At higher temperatures I move to MoS2 or hBN.
I have had a lot of galling issues with soft Ni alloys and Stainless's.
Even with different materials, different hardness, and rolled threads if one of the pieces is soft you will have issues.

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P.E. Metallurgy, Plymouth Tube

 

[Tmoose]

There are substantial differences in galling resistance of various alloys and combinations. Some combos have an EXTREME tendency gall ( at a mere 2 ksi ) as shown in charts like Table XII here -

https://www.nickelinstitute.org/med...lingcharacteristicsofstainlesssteel_9006_.pdf

I forget the SS alloys involved, but at a former precision spindle hangout we made some fancy centrifuges using gorgeous high precision ground threads on the shaft and bearing nut. The slightest tightening torque sometimes resulted in horrible galling/welding of the threads. The solution was apply to oompress the not-all-that-strong preload springs, and turn the free spinning nut into position. To rebuild the spindles the nut was machined off rather than risk the shaft threads.