Abstract
In present study mass loss behaviour of base metal and heat-treated API X70 pipeline steel in different environments such as fresh water, sea water and sodium thiosulphate medium were observed for 50 days. Corrosion is the main failure in pipeline steel which need to be reduced with the use of suitable heat treatment process. In present study two heat treatment such as HT-1 900 °C (2 hour) with tempering at 450 °C (4 hour) and HT-2 800 °C (2 hour) with tempering at 450 °C (4 hour) was used. Mechanical, microstructure and corrosion rate of HT-1 and HT-2 specimen in different environments were observed. Maximum corrosion rate (0.306 mm/y) in fresh water while minimum corrosion rate (0.181 mm/y) in sodium thiosulphate medium was observed for base metal. Maximum corrosion rate (0.224 mm/y) in sodium thiosulphate while minimum corrosion rate (0.106 mm/y) in fresh water medium was observed for HT-1 specimen. For HT-2 specimen, Maximum corrosion rate (0.192 mm/y) in sea water while minimum corrosion rate (0.099 mm/y) in fresh water medium was observed. For HT-2 specimen, maximum average hardness of (30.3 HRC) in sea water while minimum average hardness of (28 HRC) of base metal was observed. In fresh water also HT-2 specimen, maximum average hardness is (26.3 HRC) while minimum average hardness of (24.6 HRC) of base metal was observed. After that maximum average hardness of base metal (26.6 HRC) in sodium thiosulphate while minimum average hardness of (21 HRC) of HT-2 specimen was observed.