How to improve the hydrolysis stability of hydraulic oil?

May 01, 2023

What is hydrolysis stability?
The hydrolysis stability experiment of hydraulic oil is also a very important indicator of hydraulic oil.

Hydrolysis stability: The ability of an oil product to resist water reactions when in contact with water. For hydraulic machinery working in humid environments, water may enter the hydraulic oil, which is of great significance to hydraulic machinery.

When hydraulic oil comes into contact with water, the water will interact with the additive system of the hydraulic oil and the Base Oil. If the hydrolysis stability is poor, it is very easy to form acids. Hydraulic oil that lacks hydrolysis stability will hydrolyze and form insoluble inorganic salts, which may block filters and valves, inhibit hydraulic oil flow, and increase the risk of rust and corrosion in the hydraulic system. The bearing capacity of lubricants may also be reduced, and either situation can lead to premature failure of the hydraulic system.

Method for detecting hydrolysis stability
The industry standard test for hydrolysis stability is ASTM D2619-21, also known as the "beverage bottle method", which aims to distinguish the relative stability of hydraulic oil in the presence of water.

Experimental method: Seal the sample, water, and copper sheet together in a pressure resistant glass bottle, and then place them in a 93 degree Celsius oil hydrolysis stability test box. Rotate the mixture upside down for 48 hours, filter the oil-water mixture, measure the insoluble matter, and then separate the oil-water mixture. Measure the viscosity, acid value, total acidity of the water layer, changes in copper sheet quality, appearance color, and corrosion degree of the copper sheet.

However, over the years, many OEM specific formulas have increasingly strict performance requirements, requiring significant improvements in hydraulic oil performance in all fields, including hydrolysis stability. Some mainstream original equipment manufacturers have specified that the performance of hydraulic oil should be higher than industry standard testing, including ASTM testing methods. At the same time, many original equipment manufacturers have developed specialized testing methods for specific performance requirements. Each specification requirement is to ensure reliable and stable performance of hydraulic oil in constantly developing hydraulic equipment.

How to improve and maintain the hydrolysis stability of hydraulic oil?
The use of hydraulic oil with excellent hydrolysis stability can resist the interaction with water, help prolong the oil change cycle, reduce oil change costs, improve the overall efficiency of the equipment, and extend the service life of the equipment. Especially in the summer with high temperatures and increasing rainy seasons, construction machinery will face harsher and harsh environments. The requirements for various properties of hydraulic oil, especially hydrolysis stability, demulsification resistance, and thermal stability, are particularly strict.

The hydrolysis stability of mineral oil based hydraulic oil is mainly determined by the additive formula system, as well as the comprehensive platform and practical application experience. The results of different formula systems vary greatly. Market hydraulic oil additives are collected for comparative testing of hydrolysis stability.

The test uses 32 # hydrogenated Class II base oil with good quality in the domestic market to blend into hydraulic oil product oil. The finished oil blended with LZ5703 and AH31NA has excellent hydrolysis stability. The finished oil blended with two competing additives has one obvious failure and the other edge failure, which cannot meet the requirements of the national standard GB11118.1 for high pressure hydrolysis stability performance indicators.

Modern hydraulic oil formulations require advanced additives and excellent formulation technology to achieve the performance expected by OEMs and end users. Hydraulic oils with excellent hydrolysis stability can resist interactions with water, helping to extend the service life of the equipment. For oil companies, collaborating with additive partners with technical capabilities to develop formulas is essential to find the best hydraulic oil solution and provide better value to end users.

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