The paper describes a failure which serves to illustrate the complexities involved in use of creep-strength enhanced ferritic alloys, such as Grades 91 and 92, particularly in systems where they are combined with other, less creep-resistant, alloys. The case in point is recent failure of a girth weld joining main steamline piping to a main steam stop/control valve after less than 5,00 hours of operation. A post-failure assessment indicated that all design and processing associated with the sizing, welding and subsequent heat treatment of the joint had been performed consistent with the rules of the design code used A review of results of the destructive analysis of the joint is made to characterise nature of damage that caused the premature leak. This is followed by be a discussion of significant design issues that this failure has raised pertaining to a) design of the joint, and b) omission of cold spring during installation of the piping and its potential influence on the failure.
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