Rust and False Brinelling – Equipment Shut Down Threats25 Jun 2020, Posted by Industry Information in
When equipment has to be shut down for extended periods of time, you run the risk of rust and false brinelling. Both can cost a plant time and money. Let’s look at rust and False brinelling and what they mean for your equipment:
Rust (static corrosion)
Rust is the product of an electrochemical reaction that occurs when an electrolyte (like water) comes in contact with a metal surface.
• Its formation can be accelerated by the presence of contaminants in the water or on the metal itself, like scale, dust, acid, salt or alkali.
• Appearance: Rust can be red or orange FE2 (OH3) or depending on the amount of dissolved oxygen available, it can produce black FeO or Fe3O4 – a reaction that often happens very rapidly on bearing steel.
• Because the oxides of iron can often be harder than the base steel, they act as abrasive lapping compounds when the bearing is put back into service.
• The resulting pits cause concentrations of stress that reduce the load capacity of the bearing and gears, causing premature wear and failure.
• False brinelling occurs when lubricant gets squeezed out from between rolling elements and a raceway due to vibration (not rotation).
• It often happens during storage when minute ambient vibrations cause rolling elements to oscillate slightly, but not enough to generate a full lubricant film, so any subsequent metal-on-metal contact tears microparticles from high points on the surfaces.
• Appearance: Either bright polished depressions in the raceway beneath vibrating elements or the characteristic red-brown stain of fretting.
• Conditions necessary for false brinelling to occur:
1. The bearing must be under load, either from the weight of the shaft or the bearing itself.
2. The bearing must not rotate.
3. There must be an external source of vibration.
Most inactive industrial equipment is subject to all three.
Don’t let rust gain a toehold during equipment shutdowns. Let us help you protect your investment so you’re ready to roll when it’s time to start up again. Our Industrial Services team can help you determine the best course of action – saving you both time and money. Contact us today and let us get you started.