Coating on Stainless Steel Mechanical Wedge-Type Anchors

[1988honda]

Hi,

I have an application where I need to run stainless on stainless threads under a medium to high load, very similar to a mechanical wedge-type concrete anchor. My stainless combinations are a 17-4 rod and a Nitronic 60 nut. My primary concerns are eliminating the risk of galling and reduce the CoF. I know mechanical anchors run 316 rods and nuts, which are in my opinion safety critical devices. Does anyone know what coating or type of coating is used on these threads?

Thank You!

 

[TugboatEng]

The Nitronic 60 specification was made so that you don't need coatings. 316 on 316 is extremely sensitive to galling. Nitronic 60 on just about anything else is highly resistant to galling.

 

[EdStainless]

What is the environment?
How much will they be adjusted?
Any lubricant will be environment dependent.
I presume that your 17-4 is H1050 or H1100.
This is a good combination, so points for that.
Will the 17-4 have rolled threads? We used to roll then age.


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P.E. Metallurgy, consulting work welcomed

 

[1988honda]

TugboatEng - My point exactly, if the anchor manufacturers can be that confident in the coating to eliminate galling on the 316 combination, I'd like have that same level of confidence as an extra level of redundancy.

EdStainless - These will be submerged in fresh water, they will be adjusted infrequently, likely months if not years apart. The acceptance of a lubrication is not guaranteed. I am considered using an acme thread instead of a UNC thread, these will be cut, the thread is 1" diameter.

 

[TugboatEng]

Infrequent motion and submerged is going to be a challenge as you may experience crevice corrosion of the threads where covered by the nut. In this case I would suggest using a material that is slightly less noble than the stainless shaft. Aluminum bronze would likely make a good pairing with 17-4 for fresh water.

Edit: I found this document that shows 304 SS and Nitronic 60 to be a preferred combination. There is very little galvanic corrosion potential between the two. If you need the higher strength consider a more crevice corrosion resistant alloy such as Aquamet 22 for the rod and N60 for the nut.

https://www.google.com/url?sa=t&sou...AQFnoECA0QBg&usg=AOvVaw1dSw5Wmpb7sAP5MrfXwJWM

 

[EdStainless]

I would not use 304/17-4 or any straight 18Cr SS in long term submergence. This includes Nit 60.
Nit 50 has much superior corrosion resistance, this is the Aquamet 22 that TBE referred to.
It is used as boat prop shafting and is available as cold finished bar in various sizes.
I don't know how good your fresh water is, but I would usually be less concerned about galvanic issues than pitting.
Using Al bronze as the mate should be a good option.
If you want to stick with Nit 60 then consider using 2205 duplex ss as the mate.
They have good galling performance.

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P.E. Metallurgy, consulting work welcomed

 

[DAVIDSTECKER]

I use Silver anti-seize on 316 SSTL and aluminium pipe thread fittings.
It definitely solved all my galling issues.