Nonlinear ultrasonic characterization of intergranular corrosion damage in super 304H steel tube

Purpose – Super304H steel is a new fine-grained austenitic heat-resistant stainless steel developed in recent years, and it is widely used in high temperature section superheater and reheater tubes of ultra-supercritical thermal power units’ boiler. Currently intergranular corrosion (IGC) has occurred in a few austenitic stainless steel tubes in ultra-supercritical units and led to boiler leakage. The purpose of this paper is to find a nondestructive method to quickly and easily detect IGC of austenitic stainless steel tube. Design/methodology/approach – This paper uses the nonlinear characteristics of ultrasonic propagation in steel tube to detect the IGC of Super304H tube. Findings – The experimental results show that the nonlinear coefficient generally increases sensitively with the degree of IGC; hence, the nonlinear coefficient can be used to assess IGC degree of tubes, and the nonlinear coefficient measurement method is repeatable for the same tube. Research limitations/implications – A theory of how IGC would affect the ultrasonic signals and lead to a nonlinear response needs further research. Practical implications – A nondestructive method to quickly and easily detect IGC is provided. Social implications – Using ultrasonic nonlinear coefficient to assess IGC degree of tubes is a new try. Originality/value – This paper provides a new way to test IGC.