High Temperature Oxidation of Cr-Mo Steels in the Context of Accelerated Rupture Testing for Creep Life Prediction

Accelerated Rupture Testing is used to aid in assessing the remaining life for components such as pipes and tubes used in high temperature plants. Due to the high temperature nature of the test, oxide growth plays a role in affecting the test by enhancing the stress. This paper includes the study of oxide-scale growth and metal loss kinetics during air oxidation of three Cr-Mo steels used in the manufacturing of boiler tubing. These tests were carried out using cylindrical specimens similar to creep test pieces at 700°C for times up to 600 h. 1.25Cr-0.5Mo and 2.25Cr-1Mo steels showed a similar oxidation behavior, however, the 9Cr-1Mo was much higher in oxidation resistance in air. Multilayer oxide formation was observed to occur in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, involving oxides with various compositions. This paper also explains the ongoing investigations at Monash University regarding the high temperature oxidation of Cr-Mo steels and the role of oxidation in affecting the accelerated creep tests.