The “Linde Test” - A Screening Method for Biodegradable Oils with Respect to Copper-Alloy-Corrosion

The compatibility of biodegradable fluids (1) with copper-based alloys was found to be an important requirement for high-pressure mobile hydraulic systems. Existing test methods (2)(3)(4), are not suitable for determining the practical requirements for biodegradable oils, nor do they encourage or contribute to further development of such fluids. Our laboratories developed a screening method capable of establishing correlation between field experience and the results of accelerated tests. 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.

Round Robin tests performed by the German VDMA also resulted in good correlations. VDMA is currently in the process of recommending standards for biodegradable oils based among others on the work described in this paper.