Thermal Behaviour of Marine Lip Seals – A Pathway Towards Condition Monitoring

Marine lip seals are commonly used in a variety of marine propulsion systems. Predicting marine lip seal behaviour, however, is difficult: the harsh conditions in which the seals operate greatly increase the likelihood of malfunction, increased wear and/or failure. Moreover, published literature pertaining to the matter is exceedingly scarce. Condition monitoring provides a pathway to addressing the main shortcomings associated with the use of marine lip seals, such operational oil spillage and costly unscheduled maintenance. This paper examines the behaviour of marine thruster lip seals in a full-scale, fully flooded environment with a view to developing the basic requirements of a condition monitoring system. Lip contact temperature was identified as a suitable variable to characterise the condition of the seal. A custom test device was built to measure the sub-surface contact temperature of a commercial thruster seal package operating fully submerged. The seal package consisted of three seals of 300 mm nominal diameter. A typical tungsten carbide coated stainless steel shaft liner was used as the counterface. The liner was drilled to accommodate thermocouples situated 0.5 mm below its surface, thus facilitating the sub-surface measurement of lip seal contact temperature. The contact temperature was measured at five points across each seal. A sub-gigahertz frequency was used to reduce attenuation when transmitting measurements through the test device. Seals were tested under conditions that simulated normal running and conditions that precipitated seal failure. The shaft rotational speed was used as the only strictly controlled experimental parameter. Shaft speed, water, bulk oil, and lubricating oil temperatures were measured. Pressure differentials across each seal were assigned, set, and measured. Results validated the viability of the proposed concept and highlighted the interdependent nature of seal behaviour in a package configuration.