In high temperature applications, dissimilar welds made with nickel-base alloy filler metals provide extended service lives as compared to similar welds made with stainless steel filler metals. Although considerable refinery experience exists, it is difficult to find published information for pressure boundary welds made with nickel-base filler metal in hot hydrogen and/or H2S services. The Amuay Refinery has used nickel base alloy filler metals to join clad piping components in a number of piping applications. This paper details the results of an analysis of clad 1?!Cr-?AMo steel hydro processing reactor effluent piping samples removed from service to assess the long term effects of hydrogen and H$ on the dissimilar weld. Results of mechanical testing and metallurgical analysis reveal that no significant loss in properties occurred. Details of the weld procedures and weld joint design are provided.
Dissimilar metal welds (DMW) are more commonly used with great success in refinery applications than is often realized. While considerable literature has been published by the power industry on this subject, very little published information exists for refining applications (Ref. 1).
Dissimilar welds by their nature combine properties of two or more alloys which can result in mixed microstructure, and adjoining regions exhibiting differing thermal expansion characteristics. However, with an understanding of the basic mechanical properties and corrosion resistance of commonly used alloys, dissimilar welds can be designed and selected much like any material selected for high temperature or corrosive services.
An example of an extreme case might be a worthwhile place to start this discussion. It is perhaps not widely recognized that one-sided full penetration nickel alloy welds are commonly used to join stainless steel piping to weld overlaid chrome-moly nozzles on hydro processing reactors operating in hot, high pressure hydrogen services.
This paper presents the results of analysis of a DMW in 321 stainless steel clad 1MCr-%Mo piping that operated without problems for 5 years and was selected for analysis to determine the effects of operating conditions on the butt weld joints. The clad piping had been installed as a replacement for solid stainless steel piping that suffered leaks resulting from chloride stress corrosion cracking (SCC).
