Effects of cyclic stress and insulation on the corrosion fatigue properties of thermally insulated pipeline

The corrosion fatigue properties of thermally insulated pipeline in synthetic groundwater were investigated by electrochemical test, corrosion fatigue test and SEM analysis. In comparing S–N curves in an air and in the corrosive environment, the fatigue life was reduced significantly due to the corrosion reaction. The effects of insulation and stress on the corrosion fatigue resistance of pipeline steel were studied through linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) during corrosion fatigue testing. The result of LPR measurement indicated that the corrosion rate was determined not by the water content of PUR foam but the magnitude of applied stress. The better corrosion fatigue property of the insulated steel was attributed to the formation of a protective rust layer under the insulation, which reduced the acceleration of corrosion process and the propagation of fatigue crack. This was confirmed by the results of EIS measurements and SEM observation.