P91 and beyond : Welding the new-generation Cr-Mo alloys for high-temperature service

Abstract

reep strength-enhanced ferritic steel (CSEF) and advanced chromium-molybdenum steels are experiencing worldwide usage. The desire to increase efficiency has introduced a need for advanced materials with superior material properties at higher temperatures. Advanced chromium-molybdenum pipe and tubing such as 9 CrMoV [P(T)91], tungsten, and/or boron-enhanced materials (i.e., Grades 92, 122, E911, 23, 24, etc.) are now being specified. The lessons learned thus far with P(T)91 weldments have truly demonstrated that CSEF steels are quite different and require significantly more attention than the P(T)22 and lesser materials. Of the candidate advanced base materials and consumables, T23 appears to have the highest priority among challenges to P91, followed by P92 and then to a lesser extent the higher chromiumand nickel-based alloys. Emphasis placed herein on Grade 91 and the importance of maintaining preheat, interpass temperature, and dangers inherent in interrupted heating cycles or improper postweld heat treatment plus detailed attention to filler metal procurement to avoid metallurgical complications is equally true for the other advanced chromium-molybdenum alloys.