Analysis of Corrosion Damage on Water Tap
Akihiro Sakamoto, Takuya Yamasaki, Masanobu Matsumura
Most of the water taps for domestic use are made of copper alloys. Their valve seats occasionally suffer damage due to corrosion and erosion as a result of water quality and seemingly cavitation respectively. The examination of damage mechanism and the development of testing methodology for selecting the durable materials to the attack were requested. In order to understand and solve these problems completely, erosion-corrosion tests were carried out on various copper alloys (five brasses and five bronzes) by using three test methods: (a) the ISO 6509 dezincification test for pure corrosion; (b) the vibratory cavitation test with eccentric stationary specimen for cavitation erosion-corrosion; and (c) the Jet-in-Slit test for flow induced localized corrosion. The materials tested were ranked in different orders of merit according to the results obtained in the three test methods. Among these rankings, the one obtained in the Jet-in-Slit test has agreed upon with the ranking order that had been determined by experiences of field engineers who engaged themselves with the troubles under practical conditions. Hence it was concluded that the damage on valve seats has been caused by the flow induced localized corrosion, and the Jet-in-Slit was recommended as the reliable test method in selecting durable valve seat materials.