Corrosion behavior of reheated CGHAZ of X80 pipeline steel in H₂S-containing environments

Microstructure evolution and hydrogen sulfide (H₂S) corrosion behavior in 5 wt% NaCl solution at 55 °C of X80 pipeline steel reheated coarse-grained heat-affected zone (CGHAZ) have been studied. Results showed that a microstructure gradient in reheated CGHAZ was generated because of the different peak temperatures in the subsequent welding thermal cycle. The size, fraction, shape and distribution of the secondary phase, martensite/austenite (M/A) constituents, in base metal, CGHAZ and reheated CGHAZ are different. A series of changes of corrosion products formed on the surface of X80 steel can be seen as the immersion process developed which affect the further corrosion behavior. Electrochemical results and corrosion morphologies in H₂S environment showed that the base metal has the best corrosion resistance, and almost no holes and cracks exist in the corrosion products formed on the surface of base metal. The intercritically reheated CGHAZ has the lowest corrosion resistance because of the coarse necklace-shaped M/A constituents.