Technical report | RTM322 Engine Bearing Red Substance Contamination and Corrosion Investigation

ABSTRACT

Defence Science and Technology (DST) were asked to investigate the nature and cause of a red gelatenous substance observed in the lubrication system of several RTM322 engines fitted to Australian Defence Force (ADF) MRH90 Taipan helicopters. The contaminant and associated corrosion had been responsible for the unscheduled removal of several engines from the ADF fleet in two tranches over a period of approximately 3 years. DST analysis revealed that a complex interaction was likely occurring involving an adverse chemical reaction between the synthetic MIL-PRF-23699 lubricant and a coating on bearings within the engine (likely a bearing preservative fluid).

Executive Summary

The Navy Aviation Systems Program Office (NASPO) requested DST analyse a red substance that had been identified around bearings in the lubrication system of several RTM322 engines. These engines are fitted to MRH90 helicopters, a sub-fleet of which are operated by the Royal Australian Navy (808 Squadron). Later investigation in consultation with Airbus Helicopters identified the same substance in several Australian Army MRH90 helicopters. DST identified the red substance as a metal quinizarate salt, which had been assessed as benign in a previous investigation involving unfiltered gearboxes on a different fleet of ADF helicopters. In the case of the RTM322 engines, however, the red substance was accompanied by significant localised corrosion around bearings in the vicinity of the red substance resulting in bearing degradation and ultimately premature engine removal.

DST analysis revealed that a complex interaction was likely occurring involving an adverse chemical reaction between the synthetic MIL-PRF-23699 lubricant and a coating on bearings within the engine (likely a bearing preservative fluid). Several other contributing factors were identified that may have accelerated the pace of bearing degradation such as water content and compressor wash detergent in the lubricant. The quinizarate is known to form around a metal species and in this case DST confirmed zinc and to a lesser extent copper were the metals causing the formation.

The contamination issue had been detected by metallic wear particles on magnetic chip detectors or prematurely blocked lubrication filters. The corrosion and subsequent metallic debris liberation had caused a significant portion of the engine fleet to be prematurely removed. Several aspects of this investigation are yet to be explained satisfactorily and evidence of the continued impact of the resulting corrosive substance is detailed.