Internal oxide thickness measurement by ultrasonic method

Abstract

ABSTRACTLong-term exposition of re-heater and super-heater tubes in fossil-fired steam boilers at high temperature causes the growth of the iron oxide scale (magnetite) on the both internal and external tube surfaces. The presence of the internal oxide scale on the water side of the tube acts as a thermal insulator reduces heat transfer through the tube wall. Persistent overheating of the tube wall is a crucial issue, which leads to a metallurgical failure of the tube. The oxide scales react as a thermal insulator on the water side and reduce the heat transfer through the tube wall. Relatively thin oxide scale contributes to a reduction of boiler efficiency and causes persistent overheating of the tube wall. The growth of internal oxide scale is a time- and temperature-dependent process with a negative impact on the remaining creep-to-rupture life.