The influence of microstructure on the protective properties of the corrosion product layer generated on the welded API X70 steel in chloride solution

In the present work, a novel heat treatment process was used to investigate the influence of microstructure alteration on the corrosion behavior of base metal (BM), heat affected zone (HAZ) and weld metal (WM) in welded pipe steel of grade API X70. The electrochemical impedance spectroscopy (EIS) measurements were carried out to study the protective properties of the corrosion product layer after 90 days immersion in a high-pH solution. The EIS results showed that, the corrosion resistance of HAZ and WM increased after heat treatment due to formation of fine and compact corrosion product layer with fewer defects.

► Heat treated welded joint exhibits more effective corrosion products layer.
► Charge transfer resistances of heat treated welded joint sub-zones are close together.
► Defects of corrosion product layer affect corrosion behavior of welded joint sub-zones.