Investigation of corrosion resistance property of cold deformed (bended) duplex and super duplex stainless steel tubes

Abstract

Cold deformation (bending) of stainless steel tubes is one of the efficient and cost effective methods to gain the required shapes of the tube that can be useful for different practical applications. Different mechanical properties can change after the plastic deformation of the material. The purpose of this study is to investigate the corrosion (basically pitting) resistant property of cold deformed Duplex and Super Duplex materials namely UNS S32205 and UNS S32750 respectively. The bended tubes 2.5ND and 5ND were studied and compared with the straight tubes of same materials. Accelerated coupon testing (ASTM G48) and electrochemical method (ASTM G61) were followed to accomplish the objective of this study. ASTM G48 Test method was performed to know about the pitting corrosion behaviour of material at different temperatures. Weight loss per unit area was measured after exposure at acidic environment at different temperature for different exposure duration. ASTM G61 method was adopted to determine the pitting potential for each specimens and also to find the crevice/pitting susceptibility for each specimen. The results show that the corrosion resistant property of material decreases with temperature. The pitting and crevice resistant properties of cold deformed duplex and super duplex tubes were found to be similar to that of straight tubes. No specific patterns were observed in weight loss of straight and bended parts. The specimens’ weight loss per unit area was found to be under the acceptance criteria according to NORSOK Standard MDS-630. Similarly, the pitting potential of straight and bended parts for both duplex and super duplex were found to be in the similar range of about 1 V. The hardness of bended material was observed to be higher than straight one but the hardness decreased slightly after accelerated coupon testing.