Wear Prediction of Strip Seals Through Conductance

Labyrinth seal assemblies are often used to reduce gas and/or steam leakage in turbines. Caulked-in continuous strip seals are one of the common forms of seals employed on both the rotating and stationary components of turbines. Labyrinth seals perform best when minimum clearances are achieved during the steady state operation of the turbine. However, the design of the turbine and its operation during transient periods of start-up, shut-down and hot re-start often result in interference between the seal components. In the case of the strip seals, this leads primarily to wear of the strip, which in effect adds to leakage. The aim of this paper is to show that strip tip heating and melting during the rub is the main mechanism of wear in the strip. Hence thermal conductivity through the strip and into the body mass in which it is caulked is the primary controlling factor in seal wear. This paper will discuss the use of thermal conductivity and geometry of the strip in predicting wear during high speed rubs against a proprietary material. A close correlation between calculated and experimental strip seal wear data with a number of seal alloys will be demonstrated. Test data will indicate that material properties such as tensile strength and hardness have a minor effect on the wear behavior of continuous seal elements during high-speed rubs.