Corrosion mechanism and failure analysis of 09CrCuSb acid-resistant steel in blast furnace gas environment

A steel mill replaced Q235 carbon steel with 09CrCuSb acid-resistant steel for its blast furnace gas pipeline, aiming to extend service life to 9 years. However, after only 3 years, leaks were detected at the bottom of the pipelines. Detailed analysis of the service environment revealed that the pipeline temperature fell below the sulfuric acid dew point temperature following wet dust removal, resulting in a bottom solution with a pH close to 2 and a high concentration of Cl − . Through detailed observations of the failed pipeline surface and corroborating simulation experiments, we determined that this condensate environment is detrimental to the enrichment of alloy elements Cu and Sb on the acid-resistant steel surface. Instead, it promotes the formation of a loose and porous corrosion product, β-FeOOH. This resulted in localised corrosion characteristics, including the absence of a protective rust layer and severe pitting corrosion, ultimately leading to the premature failure of the acid-resistant steel.