How to predict if galling will occur?

[KM]

We will be getting a new dam gate almost three times as high as an old one we already have on another dam. The detail we use to seal the existing gate on each side (where it meets the steel gain in the pier) is a stainless steel seal tube attached to the gate (hanging vertically from a chain). Water pressure presses the tube into the corner between the gate and gain when it is underwater, but the tube swings away from that corner (about half an inch or so) when it is up out of the water and no hydrostatic force is at work.

It works very well as a detail. Next to nothing for leaks, and zero maintenance. I'm wondering if we can use the same detail on the big new gate, or if the increased hydrostatic pressure is going to mean galling will become an issue.

For ballpark numbers, the gate speed is a little under 0.5 in/sec and the maximum pressure between the moving seal tube and the stationary gain will be a touch over 950 psi in the new gate. It's slow, and it is underwater (lubricated) which are all in my favour.

But how can I tell if galling is going to be a problem?

 

[EdStainless]

I can't absolutely say that it won't gall, but having dissimilar metals works greatly in your favor.
Is there any sliding motion as the gate rises?
Do the existing ones have any wear scars or scratches on them?


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Plymouth Tube

 

[tbuelna]

Galling is process that occurs at the micro level. While your 950psi contact pressure value may seem quite modest, it only describes the macro level contact conditions. Galling is a mechanical bonding process that occurs between the tiny surface asperity tips that initially come into contact at the interface between surfaces having relative motion. The contacting asperity tips undergo a constant process of welding and shearing, which results in a gradual transfer of material from one surface to the other. Over time this material transfer produces the typical "smearing" you see in galled surfaces.

In short, it is very difficult to determine if your components will gall. If there is even a tiny amount of irregularity in the contacting surfaces, due to roughness, misalignment, etc, then galling can easily occur. If you want to ensure that no galling will occur in your system, then I would suggest making one of the sliding seal surfaces from a material (ie. a polymer) that will not mechanically bond to the mating metal surface.

Hope that helps.
Terry

 

[KM]

Interesting--thanks for the replies!