Abstract
In order to get rid of the preferential corrosion problems occurring in the welded joint of line pipes transporting oil and gas containing CO2, the effects of the chemical composition of heat affected zone (HAZ) and weld metals on the preferential corrosion property in CO2 containing environment were investigated. Electrochemical polarization and galvanic current density measurements were carried out to examine the preferential corrosion of welded joint in synthetic sea water saturated with 0.1 MPa CO2. The effect of base metal chemistry, seam and girth weld metal chemistry of line pipes on the preferential corrosion of HAZ and weld metals was investigated. The effect of base metal and HAZ microstructures on HAZ preferential corrosion property was also investigated.
HAZ preferential corrosion is not likely to occur in Cu and Ni bearing steel whose microstructure consists of bainite. The chemical composition of weld metal and base metal affect the preferential corrosion behavior of the welded joint and the addition of Ni and/or Mo to the weld metals is effective to prevent the preferential corrosion of the weld metals regardless of welding methods.
