Study of Erosion Shield Failure in Powerplant Steam Generator

Abstract This report gives a comprehensive investigation on the failure of Erosion Shields in the steam generator of a coal-fired power plant. The primary purpose of the Erosion Shield is to safeguard the superheater tube from potential erosion caused by the forceful discharge of soot blower and to mitigate the occurrence of slagging. In certain instances, it has been observed that Erosion Shield clamps may fracture and descend to the lower region of the steam generator, hence causing disruption to the operation of the bottom ash management system. In order to safeguard the superheater tube, the Erosion Shield is affixed and secured by the use of clamps and welding. Based on the observed data, it can be concluded that instances of failure are observed in both the clamp and weld components. In order to conduct a more comprehensive analysis, metallographic specimens of the clamp are made and subjected to hardness testing. The hardness of the weld metal is greater in comparison to the hardness of both the heat-affected zone (HAZ) and the base metal. The disparity in hardness between the E308 filler metal and the AISI 304 base metal is quite substantial. The analysis of the macrostructure reveals that the weld bead on the clamps exhibits an excessive height. This phenomenon can be attributed to the reduced bending angle shown by the clamp at its terminal point. The microstructure analysis of the Erosion Shield sample involves the study of certain test locations located in the base metal, heat affected zone (HAZ), fusion line, and weld metal. Sufficient characterization of the Erosion Shield material as austenitic stainless-steel type can be achieved by analyzing the microstructure of both the base metal and the heat-affected zone (HAZ). The observed grain structure of both the base metal and heat-affected zone (HAZ) did not exhibit any discernible differences. This can be attributed to the prolonged exposure of the Erosion Shield in a high-temperature gas environment ranging from 1200 to 1400°C. Furthermore, there is a lack of evidence suggesting the presence of intergranular corrosion at the grain boundary of both the base metal and heat-affected zone (HAZ).