Effect of Normalizing on Impact and Corrosion Resistance of Low-temperature Service Seamless Steel Pipe

Abstract

The seamless line pipe, which has fine low temperature impact properties for Low-temperature Service and good H2S corrosion resistance, was investigated through chemical composition designing, optimizing smelting-rolling processes, and heat treatment processes following ASTM A333 standard. The influence of normalizing on the impact property and corrosion resistance was studied by optical microscope, scanning electron microscope, transmission electron microscope, mechanical test and corrosion test. It is demonstrated that the low temperature mechanical properties and anti-H2S corrosion properties of hot-rolled trial-pipe and normalized trial-pipe meet ASTM A333 standard. The microstructure of hot-rolled trial-pipe is pearlite and ferrite, and the grain distribution is uniform and grain size is fine. The dominated precipitates phase are TiN particles in hot-rolled trial-pipe. Ductile to brittle transition temperature is determined at -60 °C. The grain refinement is achieved after normalized and the main precipitates are TiN particles together with a few VN particles. Ductile tobrittle transition temperature was further lowered, at - 80 °C. The corrosion behavior of the material was examined by hydrogen induced cracking (HIC) corrosion test, sulfide stress corrosion (SSC) test and polarization test at various polarization scanning rates. It is observed that the anti-HIC corrosion performance and SSC corrosion resistance are similar for both hot-rolled and normalized pipes, but the performance of electrochemical corrosion of normalized pipe is better than hot-rolled pipe, which indicates that the normalized pipe is more suitable for demanding corrosive environments.