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

Abstract

Accelerated creep rupture testing is used to aid in assessing the remaining life for components such as pipes and tubes used in high temperature plants. At the high temperatures, oxide growth can affect the creep results by diameter reduction and, thus, increase the stress. This paper includes the study of oxide-scale growth and diameter reduction kinetics during air oxidation of two Cr-Mo steels used in the manufacture of boiler tubing. Tests were at 500–700°C for times up to 1000h for 1.25Cr-0.5Mo and 2.25Cr-1Mo steels (using cylindrical specimens similar to those used for creep testing). At 500–600°C, 2.25Cr-1Mo steels showed a superior oxidation resistance than 1.25Cr-0.5Mo steels. However, at 700°C, the oxidation resistance of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels was similar. Multilayer oxide formation was observed to occur in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, involving oxides with various compositions. It is suggested that inaccuracies in creep data may arise as a result of the cross-sectional losses of the specimens. This inaccuracy may also cause discrepancies in life assessment.