Microstructural Evaluation and Corrosion Resistance of a Dissimilar Joint between a High Strength Low Alloy Steel and a Duplex Stainless Steel

Abstract

The union between two dissimilar materials has been widely applied in the oil and gas industry. In general, this type of welding is more sensitive to differences in chemical composition between the metals involved. From this perspective, this work aims, by autogenous welding, to evaluate the microstructure of a joint welded between a high strength and low alloy steel of class API 5L X80 and a duplex stainless steel UNS UNS S32304. Furthermore, the corrosion resistance of the dissimilar welding region was evaluated in a solution which simulates the seawater environment. The microstructural properties and composition of the welding region were studied using optical microscopy, scanning electronic microscopy (SEM) with energy dispersive spectroscopy (EDS). The corrosion resistance was studied by anodic potentiodynamic polarization and by electrochemical impedance spectroscopy. The dissimilar region differs from both materials in their microstructural characteristics and presented significant migration of chromium and nickel from duplex materials to the dissimilar region, which enhanced their corrosion resistance compared with the API. Therefore, we concluded that the dissimilar regions are compatible with the applications which allow taking the advantage of join these two materials.

Key-words:
Welding; Dissimilar; API; Duplex