Effect of temperature, pH and sulphide on the cavitation erosion behaviour of super duplex stainless steel

Cavitation erosion characteristics of super duplex stainless steel UNS S32760 in 3.5% NaCl solution with controlled temperature, pH value and sulphide content have been studied by means of a 20 kHz ultrasonic vibrator at a peak-to-peak amplitude of 50 mu m. The erosion behaviour was compared with that of austenitic stainless steel UNS S30400. It was found that the mean depth of penetration rate (MDPR) for S32760 and S30400 initially increased with temperature from 10 degrees C to 50 degrees C, and reached a maximum at about 50 degrees C and then decreased with further increase in temperature to 70 degrees C. Results of MDPR versus pH at 23 degrees C indicated that S32760 is more sensitive to change of pH than is S30400 at 23 degrees C. Also, there exists a minimum MDPR at pH 9 for S32760. For S30400 and S32760 in 3.5% NaCl solution with various sulphide concentrations, the MDPR increased gradually as sulphide concentration was increased. S30400 was found to be more sensitive than S32760; to the effect of sulphide on cavitation erosion. The cavitation erosion behaviour of S32760 at varying temperature, pH and sulphide content is explained with the aid of polarisation studies. (C) 1997 Elsevier Science S.A.