Cavitation erosion tests has been conducted at an inlet pressure of 20MPa with a low Cv-value angle valve inserting a needle-type contoured plug. Under a flow-to-open set up, the plugs made of Stainless Steel-316 were eroded mainly in a confined area around the seat joint taper. The history of the weight loss caused by the erosion is found to be subjected to a power law to the working duration. A deterioration in the valve performance as a failure of the shut-off function or a complete damage on the entire characteristic surface is diagnosed in terms of the cause of the erosion development. If a valve operation is monitored for an entire duration, a limit for replacement of the plug will be predicted by the presented power law. For an estimate of the weight loss, the plug should have the surface carefully machined and be arranged concentrically with the seat ring since the initial roughness and the eccentricity affect the erosion development significantly.
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