Dissimilar metal welds (DMWs) have been used successfully in many corrosive and severe service environments. In recent years, strict limitations have been imposed on DMW use in all environments. Current criticality service guidelines for petrochemical plants demand a fit for purpose re-evaluation of DMWs. DMW implementation requires an in-depth review of welding metallurgy and the potential corrosion mechanisms. Success with DMWs in severe service depends largely on the fusion boundary morphology, dilution limits, mechanical and chemical properties, chemical composition of the deposited weld metal, and micro-segregation. These factors need to be evaluated in conjunction with a variety of conditions such as process stream, temperature, weld configuration, stress regime, fatigue, creep strength, and corrosion mechanisms. This paper discusses how DMWs can be reliably incorporated into severe service by presenting practical DMW guidelines for today’s petrochemical plants that address weldability, selection of filler metal, and weld procedure qualification. Case histories of industry use of DMW are also presented.
Keywords: Dissimilar Metal Welds (DMWs), Intermediate Mixed Zone (IMZ), Fusion Zone Microstructure, Dilution, Carbon Migration.