44040

Anti-galling plating help required please!  

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Hi all,
I have a problem with some parts manufactured from Aisi 420 steel which galls very badly on a stub acme thread. We currently copper plate the thread (0.003" thick) to prevent this, but I'm not convinced that this is the best plating choice. Can anybody recommend any plating.

These parts are used in a downhole environment and subjected to H2S and CO2. Temperature is 150°C max.

Thanks,
Leo Hinton

Leo Hinton
- Verwood, Dorset, UK

I would have suggusted silver or tin until you said sulfide. I would investigate using between 0.0005 and 0.001 of electroless nickel on the male threads. It is harder than copper but will plate relatively evenly, so should work.
What is wrong with using teflon tape?

James Watts
- Navarre, Florida

Sounds like an excellent application for electroless nickel/teflon.

Jeffrey Holmes, CEF - Spartanburg, SC, USA

In the past I have used silver plated onto the stainless steel to overcome galling problems, but I see this application will be aexposed to H2S, so it may not be suitable. I used a cyanide silver strike system and it seemed to work OK. However, if silver is no use, it may be worth trying a gold coating - bit expensive but it probably will work.

Trevor Crichton R&D practical scientist - UK

Hi James,

Thanks for the information. I'm going to give the Nickel a shot and see what happens.

Although teflon tape would probably be very successful, I am a little bit caution of using it as we have o'rings at every threaded interface. A piece of tape could work it's way across the sealing face can compromise the joint.

Thanks again,
Leo Hinton

Leo Hinton
- Verwood, Dorset, UK