Failure analysis of superheat tube 2.25Cr-1Mo in biomass power plant

Abstract

The understanding of microstructures, their influences, and failure mechanisms are of necessary for determining lifetime and failure behaviors of metal parts being used in some severe environments. This research aims to study the failure causes and mechanisms of superheat tube used in a power plant. The tube examined in this experiment was 2.25Cr-1Mo (SA213 Grade T22) with a diameter of 33.5 mm and 4.33-mm wall thickness. This tube had been in-service for 7.5 years in a 9.9-MW biomass power plant. Visual inspection, chemical analysis with an optical emission spectrometer, optical microstructure, scanning electron microscope (SEM), energy dispersive X-ray (EDS), hardness measurement and tensile were employed to investigate the causes of superheat tube failure. The results showed that the damaged tube was subjected to the non-uniform loss of outer wall thickness due to erosion and presence of ferrous oxide at the outer tube surface. The hardness of outer and inner tube surfaces was found to be less than that of the mid-wall section. In addition, carbide particles were observable and uniformly dispersed throughout the microstructures. Regarding the SEM result, the tube failure was relevant to the bursting with ductile fracture.