The hydraulics industry is increasingly moving toward environmentally acceptable fluids. However, the overall performance of most biofluids has, thus far, been disappointing. A key issue is the fluids’ compatibility with soft or yellow metals and alloys. Conventional corrosion testing — such as DIN 51759/ASTM D 130 “Copper Strip Corrosion Test” or ASTM 2619 “Hydrolytic Stability Test” — does not adequately demonstrate real world performance.
VDMA, a key association service provider and the largest engineering industry network in Europe, lead by Linde Pumps, sought a more meaningful test for both mineral oils and biodegradable fluids. Together, VDMA and Linde developed a screening method capable of establishing correlations between field experience and the results of accelerated testing.
Test parameters include copper-alloy materials, temperature, different mixtures of biodegradable oils with mineral oils and water, as well as the simulation of mechanical activation of the corroding surfaces. It is suggested that the “Linde test” provides a simple, quick, and low-cost laboratory method to determine the compatibility of biodegradable oils with copper alloys in hydraulic systems under conditions representative of practical applications.
The procedure, although simple, is very severe. The fluid is contaminated with petroleum oil and water. It is then heated to 120° C (248° F), and sample strips of metal are added. The fluid and sample strips are agitated with glass beads that work to grind the test samples. The samples are weighed after 96 hr, and the mass loss is determined. The samples are also evaluated for corrosion and are rated none, weak, strong, and extreme. Typically, brass (CuZn35Mn2Si), cast bronze (CuPb15Sn8), sintered bronze (CuPb10Sn8), and bearing steel 100(Cr6) are used.
As part of a project with National Oilwell Varco (NOV), Terresolve Technologies Ltd. ran its readily biodegradable and non-toxic EnviroLogic 3068 hydraulic fluid against this very severe protocol. The results have been favorable.
The majority of the biodegradable lubricants use synthetic esters as base fluids. To make a synthetic ester, a triglyceride (typically vegetable oil) is mixed with acid and alcohol. The reaction gives off water and heat. In a lab, the synthetic ester has excellent properties. However, in the VDMA 24570 test, adding water and heat back into the fluid causes a reverse reaction that makes acid, alcohol, and vegetable oil. The acid attacks metals and seals, and the vegetable oil is subject to breakdown under temperature.
Terresolve has taken a different approach. Its EnviroLogic 3068 is made from Biopolyolefin which does not hydrolyze (break down when mixed with water). Therefore, it is more stable in hot, wet conditions. Also, EnviroLogic 3068’s high thermal stability allows it to withstand temperatures in excess of 300°F.
EnviroLogic 3000 series of fluids include ISO viscosity grades 32, 46, 68, and 100. All have met or exceeded VDMA 24570 and other tests. In addition, it has performed in tens-of-thousands of hours in the field, under all kinds of conditions. This performance, combined with its biodegradability and non-toxicity, make it a logical choice when hydraulic equipment must work in sensitive environments.