Characterization of Tube Repair Weld in Thermal Power Plant Made of a 12% Cr Tempered Martensite Ferritic Steel

Abstract

The heat resistant tempered martensite ferritic steel X20CrMoV121 (DIN) has been extensively used within the last few decades as a material for boiler tubing systems and pipelines in thermal power plants (TPP). Long-term behavior of this steel is vastly researched and very well known, but main disadvantage is its poor weldability. In situ welding of martensitic steels is always challenging task and is usually quite difficult to implement properly in a short time, during forced outages of TPP. In this paper, characterization and mechanical properties of undermatch welded joint made during partial replacement of boiler outlet superheater (SH) in TPP by austenitic filler material, after 10 years of service are presented. Due to "cold" technique of welding, which does not required post weld heat treatment, this procedure were regular and widely used repair welding technique in two TPP (620 MW) units. In the purpose of comparison, two other type of matching welding joints of the same SH were also characterized: shop welded joint made by electrical resistance flash butt welding, as well as field welded joint made by gas tungsten arc welding during assembling of SH, which were both in service approximately 150,000 h.