Electrochemical Corrosion Behavior of X90 Pipeline Steel and Its Heat-affected Zone in Acidic Medium

X90 pipeline steel was subjected to a thermal cycle and a secondary thermal cycle using a Gleeble 3500 heat/force simulation machine. The microstructures of the X90 pipeline steel and its heat-affected zone were observed by scanning electron microscopy. The electrochemical properties of the original structure of X90 pipeline steel and its heat affected zone (HAZ) in different pH Yingtan simulated solutions were studied and compared. The results show that when the pH of the solution was 3.3, the electrochemical impedance exhibitted an inductive resistance characteristic, and the surface of the sample was activated and dissolved. Relative to the original structure of X90, the coarse grained HAZ (CGHAZ) and the critical coarse grain HAZ (IRCGHAZ) had larger surface activity and better corrosion resistance, when the pH of the solution was 4.7 and 6.1, the electrochemical impedance only exhibited capacitive reactance characteristics, and the surface of microstructure was in a state of film corrosion, the product film on the surface of the grain refinement fine grain zone HAZ (FGHAZ) and the supercritical coarse grain zone HAZ (SCCGHAZ) was denser and more stable, the corrosion current density was smaller, and the corrosion resistance was better.