What Causes Galling of Pump Materials?

Sulzer Pump Service Reliability Tips

Material Galling & Hardness Differential

What causes galling of materials? 
A gall results from wear caused by adhesion between sliding surfaces. When a material galls, some of it is pulled with the contacting surface, especially if there is a large amount of force compressing the surfaces together. 

Galling is caused by a combination of friction and adhesion between the surfaces, followed by slipping and tearing of the crystal structure beneath the surface.

Galling example

Why a Differential?  
In general, for good galling resistance, a minimum hardness differential up to 100 Brinell Hardness Number (BHN) is needed. While API 610 requires a minimum 50 BHN differential, Sulzer improves on that by requiring 100 BHN differential.

However, if both rotating and stationary materials are very hard (>400 BHN per API 610), then the differential is not as crucial to maintain.   

Many other factors go into establishing close clearance material combinations, and although non-galling performance is typically a priority, it might not be the only factor.

Sulzer has vast testing, research and experience in material couple choices for providing the best performance for your situation.    

Sulzer Pump Services (US) Inc.
Email: [email protected]

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