Leshchak R. Method for corrosion damaging assessment of welded joints of pipes with dissimilar steels

Research object: circumferrential welded joints of powerplants steamheater pipes (12Х1МФ steel and 12Х18Н10Т steel) with different exploitation time. Purpose of work: developing of assessment of corrosion damaging of dissimilar welded joints methodic which is based on the basic electrochemical characteristics of the welded joint materials and calculating procedure of determination of corrosion current density on the internal surface of the pipe, which considering the combined welded joint as a threeelectrodes electrochemical system. Methods of researces: voltamperometric electrochemical methods for experimental determination of the basic corrosion characteristics of the welded joints materials; materialscience methods for microhardness and surface chemical composition of welded joint components determination; mathematical physics methods for analytical description of corrosion currents on the internal surface of the pipes near-by the welded joint; numerical methods for calculation of depth and character of corrosion damages on the internal surface of welded dissimilar pipes. Considering of welded joints of dissimilar pipes as a three-electrode electrochemical system, an analytic procedure for the evaluation of corrosion current density distribution at the welded zone is proposed. On this basis the experimental-numerical method for prediction of profile and maximum depth of local corrosion defects in the components of welded joints has been developed. The data on general characterisation and maximal depth of localised damaging on internal surface of pipes were received and analysed with dependence of term exploitation and composition of operating environment. In particular, the possibility of changing the polarity of local galvanic couples in the vicinity of the welding zone depending on the period of operation has been shown and that cannot be predicted within the framework of the existed approaches. Proposed model and received data can be served as basis for prediction of the given welded joint behaviour during long-term exploitation with the aim to prevent the catastrophic situations.