What is the hydrolytic stability of lubricating oil?

The hydrolytic stability of lubricating oil refers to the ability of the components (base oil and additives) in lubricating oil to remain stable and not decompose in the presence of water. Lubricating oil with good hydrolytic stability is relatively stable. The test standard for lubricating oil hydrolytic stability is ASTM D2619-09.

1. Which lubricants are more likely to hydrolyze:

Lubricants are hygroscopic, so they absorb moisture from the air. Different base oils have slightly different hygroscopicity. Ester oils, especially polyol esters and phosphate esters, are relatively hygroscopic.

The hydrolysis stability of lubricants is related to the ingredients of the formula. Some additives are easy to hydrolyze. For example, some anti-wear oils contain ZDDP anti-wear agents. This anti-wear additive is relatively easy to hydrolyze and produce acidic substances.

Some base oils are relatively easy to hydrolyze. When selecting oil, the moisture problem of the use environment and the type of base oil should be considered. For example, ester oils are relatively easy to hydrolyze. If ester oils are used under conditions of heavy moisture and humidity, attention should be paid to the waterproof maintenance of the oil. Lubricants with better hydrolysis stability have a relatively long time to resist hydrolysis and can withstand a relatively high moisture content, but they will still hydrolyze over time. Therefore, it is necessary to strictly control the problem of water ingress into the lubricant and deal with it early.

2. Consequences of lubricant hydrolysis

Lubricant hydrolysis will change the physical and chemical properties of the oil, causing poor lubrication and damage to the machine. In addition, the products of hydrolysis are also harmful to the machine.

1) Lubricant hydrolysis will cause the appearance of the oil (color, transparency) to change.

2) Formation of acidic substances: The most common consequence of lubricant hydrolysis is the formation of acidic substances, and most of them are carboxylic acids. Compared with sulfuric acid, carboxylic acids are weaker, but they can also damage the machine. The acidic substances generated by hydrolysis can be monitored by oil detection FTIR technology.

3) Decrease in lubricant viscosity: Hydrolysis will cause the viscosity of the lubricant to decrease - compared with acidic substances, the decrease in viscosity will damage the machine more directly and quickly. When the viscosity decreases, when the oil film's carrying capacity is insufficient, friction between metals occurs, which wears the machine.