Pitting corrosion resistance properties of super duplex stainless steel weld metals and influencing factors

Thanks to the excellent combination of strength, low temperature toughness, and good corrosion properties, particularly resistance to pitting corrosion attack, super duplex stainless steels have found wide applications in the offshore–onshore oil and gas industries and petrochemical industries. In the meantime, due to the special thermal process of welding, super duplex weld metals in the as-welded condition, when comparing with the base steels, always show considerably inferior corrosion properties. However, in order to maximize the performance capability of processing facilities built with super duplex steels, oil companies have been continuously trying to push the required pitting temperature for weld metals to more and more challenging levels. This has made the design of relevant welding consumables even more difficult. This paper explores the possible solution through optimizing the alloying design so that the weld metals can consistently meet the increased requirements of various specifications. This includes a balanced alloying system that will provide good pitting corrosion resistance (typically expressed as high critical pitting temperatures) while is still capable to maintain adequate mechanical properties, particularly low temperature impact toughness. Major aspects that may have considerable influence on these properties are investigated and discussed.