Today, there are several categories of environmentally acceptable lubricants (EALs) available for vessel owner/operators and equipment manufacturers. Most EALs are ester-based oils that have been approved by seal system manufacturers. Depending on what the ester oil is derived from, it will exhibit widely different performance characteristics.
How different ester oil types perform
Natural Type: These ester-oil formulations use triglyceride esters from vegetable or animal sources.
Performance issues: Although triglyceride-based ester oils are used in hydraulic applications and as a base for biodegradable greases, their performance is significantly degraded in the presence of water and high temperatures.
Esters derived from vegetable resources have simple, linear molecular structures with carbon-carbon double bonds. This type of molecule is referred to as an “unsaturated ester,” because the molecule is not “fully saturated” with hydrogen atoms. The unsaturation causes this type of ester to be particularly susceptible to breakdown in the presence of water and heat, a process known as hydrolysis.
Synthetic Type: These ester-oil formulations are derived by combining acids and alcohols during manufacturing. Synthetic esters are prepared by reacting carboxylic acids with alcohols. The characteristics of each synthetic ester type are determined by the acids and alcohols that are chosen.
Performance issues: Synthetic-based ester oils can resist temperature and water degradation—but the right type of ester must be selected. A good choice for marine applications is saturated esters prepared from branched acids—known as polyolesters. These complex polyolester molecular structures (also known as sterically hindered esters) are very stable in water.
The bottom line
While all esters can be affected by water through a process known as hydrolysis, field experience with saturated synthetic polyolesters is very positive. In fact, even when mixed in 300 to 500 ppm water, they resist hydrolytic breakdown for years. What have you experienced? Post a comment below.