Influence of Moisture on Bearing Life

The hazards of moisture are reflected in two aspects: direct damage to the metal surface, and damage to the lubricating oil/grease, the latter indirectly causing bearing damage.

The hazards of water to bearings are in the following ways:

1. Hydrogen-induced cracking:

Also known as hydrogen embrittlement or hydrogen damage, it can cause metal damage, but it has not received extensive attention in the manufacture and maintenance of bearings. For this type of situation, water may be a part of the source of hydrogen. Electrolysis and corrosion can also produce hydrogen. Promotes electrolysis and corrosion. High-strength steels are particularly vulnerable to this problem. In addition, the additives added to lubricating oil and grease contain sulfur (extreme pressure additives, anti-wear agents, etc.). Mineral oil itself also contains certain sulfur impurities, which will promote metal corrosion and cracking. Both humid atmosphere and free moisture may cause hydrogen embrittlement of metals.

2. Corrosion:

Water will cause metal rust and corrosion. After corrosion damage is formed on the surface of the bearing raceway, the smoothness of the lubricating oil film will be destroyed, resulting in poor lubrication and further aggravated damage.

3. Oxidation and deterioration of lubricating oil:

Water will promote the oxidation and deterioration of the base oil in the oil. If high temperature and impurities (such as fine metal grinding debris) are added, the oxidation rate will increase significantly.

In addition, water will also cause the loss and consumption of antioxidants in the lubricating oil, leading to oxidative deterioration of the lubricating oil. The oxidation of lubricating oil will form acidic substances, the paint film on the metal surface, and the viscosity of the oil will increase, leading to metal corrosion, affecting metal cooling and the normal function of certain parts.

4. Consume the additives in the oil:

The main component of lubricating oil and grease is base oil, and there are some additives. In addition to antioxidants, there are other additives such as anti-wear agents, extreme pressure agents, rust inhibitors, detergents and dispersants, demulsifiers and so on. Water can cause additives to hydrolyze, agglomerate, and lose. Certain sulfur and phosphorus extreme pressure agents will denature in the presence of water, generating sulfuric acid or phosphoric acid, increasing the acid value of the oil, and forming a corrosive acidic environment.

5. Affect the normal flow of lubricating oil:

Water will cause sludge and oil to emulsify. These agglomerated impurities are suspended in the oil and affect the normal flow of the oil. In addition, these impurities will also accumulate in the oil supply holes of the bearing. Other hazards are the clogging of the filter element. In severe cold weather, the water in the oil may freeze, which also causes the oil flow to be poor and the machine lacks oil.

6. Increased bubbles:

Moisture will affect the surface tension of the oil, causing the bubbles in the oil and the foam on the surface of the oil to increase. For general oil, only 1000ppm of water in the oil will cause serious foam problems. The consequence is that the metal surface cannot form a complete surface. Lubricating oil film, a series of problems will follow: increased oil temperature, increased oxidation, metal cavitation, and poor oil flow will cause damage to the bearing. Sometimes the bubble problem can also affect the normal operation of the oil slinger or the oiler.

7. Affect the strength of the oil film:

Bearing lubrication relies on the lubricating oil to form an oil film between two metal contact surfaces. The oil film separates the direct friction between the metals and protects the metal. If water enters the bearing metal contact area, it will Destroy the integrity of the oil film and reduce the strength of the oil film. For heavy-load, low-speed bearings, this hazard is particularly obvious, causing metal fatigue damage, metal scraping, and chipping.

8. Breeding bacteria:

Water can breed bacteria, microorganisms, and fungi. The main hazard of these substances is to affect the normal flow of oil. In addition, they can block the filter element, form corrosive substances, cause lubricating oil and grease to rot and deteriorate, and indirectly harm the bearing by affecting lubrication.

9. Loss of lubricating oil and grease:

Water will cause oil loss through scouring. In addition, some greases will soften when immersed in water. With the loss of water, the thickener used in some greases is not resistant to water and will soften and lose during water scouring and splashing.


From the text, we can see that the hazards of water to bearings are mainly reflected in a series of chain reactions. Therefore, it is necessary to prevent water from entering at the source, and prevent grease and lubricating oil from contacting moisture during storage, transportation, and use to prevent bearings damage.

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