ROOT-CAUSE ANALYSIS OF SUPERHEATER-TUBE FAILURE

摘要

Superheater-tube failure is listed among the major causes of a fossil-fuel-fired boiler outage. Therefore, it is necessary not only to identify and repair it in the case of failure but also to eliminate the root cause of this problem. As there may be multiple reasons of failure in exposed equipment such as a superheater, a thorough investigation of more than one probable cause is usually required. This article focuses on a failure analysis of a boiler located in a chemical plant. After a leak was discovered, several cracks on the superheater tubes were identified as its main cause. It was necessary to assess the extent of the damage, detect the root cause and propose corrective actions. Two problematic locations with cracks were identified during the visual inspection: the first was on the superheater-tube bends and the other was the weld joint between the superheater and the transition pipe. As the first step, the material-microstructure and composition analyses of the tubes in these critical locations were carried out. Even though small weaknesses were found in the microstructure, the main cause of the tube failure was not identified. As the next probable cause, thermal-dilatation stresses were investigated using the finite-element analysis (angl. FEA). The support system, consisting of fixed and spring supports, as well as the compensator were included in the analysis that confirmed the thermal-dilatation stresses as the major cause of the failure. Based on the results, a new technical solution for the supports was suggested and verified with the FEA.