Evaluation of options for weld repair of Grade 91 piping and components: metallographic characterisation

摘要

Creep strength enhanced ferritic (CSEF) steels such as Grade 91 are the preferred materials for many of the high temperature boiler tubing and piping components used in modern power generating plants. Validation of temperbead welding techniques is particularly important for Grade 91 steel as accurate post-weld heat treatment (PWHT) has proven to be difficult in field applications. Even a well-controlled PWHT can degrade the base material strength, and a poorly performed heat treatment can lead to subsequent creep properties being below the minimum expected by codes. Successful demonstration of temperbead techniques for Grade 91 steel would alleviate these concerns and create additional options in designing a ‘well-engineered’ repair. This article presents the results from a project evaluating options for field repair of Grade 91 components. Metallographic characterisation of the welds produced is described with future publications providing results from cross-weld creep testing and post-test examination.