Understanding and managing the safety and reliability issues of ocean energy converters is a key factor in the development of viable technologies. This requires mathematical models that enable numerical solution with the sufficient accuracy and computational efficiency. In this study a point absorber has been chosen as an example of a wave energy converter (WEC). The converter has been modelled by using bond graphs – a systematic and useful method for systems spanning several energy domains. In the hydraulic system of the WEC, the piston ring and cylinder play very important roles in achieving desired energy converting performance and durability. In this paper, an abrasive wear model for the piston ring and cylinder is developed during the steady state operation by using the Archard's abrasive wear equation. Based on time domain simulation results for the full conversion system, the development of wear in the piston ring is modelled as a function of the contact pressure and relative motion. The procedure to determine the time to failure due to the scuff for the ring is calculated for a case with one sea state only.