RE: [PSUBS-MAILIST] Stainless Steel Galling

Brent,

A heavy coat of a molybdenum-based anti-seize compound to threads prior to applying a nut will go a long ways to avoiding galling. This is a big concern on valves in nuclear systems as they stainless steel and have a threaded cap that covers the valve stem and packing…galling was of particular concerning in these cap threads.

R/Jay

Respectfully,

Jay K. Jeffries

Andros Is., Bahamas

As scarce as the truth is, the supply has always been in excess of the demand.

-Josh Billings

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Brent Hartwig
Sent: Wednesday, December 24, 2008 12:15 PM
To: PSUBSorg
Subject: [PSUBS-MAILIST] Stainless Steel Galling

I trust all you Submadmen are having a great day. Just don't try to go shopping today. As for me it's all about the quality of the snow shovels, and gas for the snow blowers.

I found the below data interesting in regards to preventing SS threads from galling. I usually just use teflon pipe dope to keep the SS threads from galling.

Properties

"High oxidation-resistance in air at ambient temperature are normally achieved with additions of a minimum of 13% (by weight) chromium, and up to 26% is used for harsh environments.^[7] The chromium forms a passivation layer of chromium(III) oxide (Cr₂O₃) when exposed to oxygen. The layer is too thin to be visible, and the metal remains lustrous. It is impervious to water and air, protecting the metal beneath. Also, this layer quickly reforms when the surface is scratched. This phenomenon is called passivation and is seen in other metals, such as aluminium and titanium. When stainless steel parts such as nuts and bolts are forced together, the oxide layer can be scraped off causing the parts to weld together. When disassembled, the welded material may be torn and pitted, an effect that is known as galling. This destructive galling can be best avoided by the use of dissimilar materials, e.g. bronze to stainless steel, or even different types of stainless steels (martensitic against austenitic, etc.), when metal-to-metal wear is a concern. In addition, Nitronic alloys (trademark of Armco, Inc.) reduce the tendency to gall through selective alloying with manganese and nitrogen."

en.wikipedia.org/wiki/Stainless_steel

Regards,
Szybowski