Mechanical properties and corrosion resistance evaluation of superduplex stainless steel UNS S32760 repaired by GTAW process

Abstract

Superduplex stainless steels (SDSSs) are alloys widely used in the exploration and production of oil. They are used in marine and offshore components such as heat exchangers, umbilicals, sea water injection lines and various other equipment that requires high corrosion resistance with elevated mechanical strength values. These characteristics are due to its fine two-phase microstructure composed of similar proportions of austenite and ferrite and the alloying elements of Cr, Ni, Mo, N and W. However, during welding, and also in the stages of fabrication and pipe assembly, the presence of defects may occur that requires the need for repair procedures to be carried out on the welded joint. This study aims to characterise the microstructure, mechanical properties, nitrogen content and critical pitting temperature (CPT) of a SDSS pipe, UNS S32760, in certain regions of a welded joint, where the gas tungsten arc welding process was performed, with the completion of two sequential repair procedures. The results show that there is a decrease in the value of the CPT at the root of the weld, though there are not substantial variations in the mechanical properties analysed.

Keywords:

• Superduplex stainless steels
• welding repair
• mechanical properties
• corrosion resistance