Failure case study on reheater pipes in a subcritical unit served for a thermal power plant

Abstract

Leakage failure occurred in the reheater pipe of a subcritical unit after 9 years operation, but didn't reach the design lifespan. Multi test and analysis methods were applied to find the failure reason and mechanism. The results show that the main failure mode is the thinning of the pipe wall caused by high temperature corrosion, the metal loss of the pipe wall is more than 25 %. Through the analysis of the structure and composition of the corrosion products, it is found that the corrosion products of the pipe wall are divided into three layers, while a large number of pores exist between the corrosion products and base material, hereby, the corrosive substances can continuously reach the surface of the base material. The content of sulfur and oxygen in the corrosion layer on the side of pipe wall is high, and the percentage reaches 20.95 % and 49.17 % respectively. It is proved that sulfur is the main factor affecting the high temperature corrosion of reheater pipes, and sulfate is produced by the combined action of sulfur and oxygen. Under the continuous action of high temperature sulfur corrosion, the local pipe wall of the pipeline is thinned and eventually leaks.

Keywords

• Reheater pipe
• Leakage
• High temperature sulfur corrosion
• Thinning