Applications of advanced low-alloy steels for new high-temperature components

The new low-chromium steel grades 23 and 24 are candidate materials for components of the new power and petrochemical plants, and for the refurbishment and re-powering of older plants. The mechanical and creep properties of both grades are significantly better than the parent grade 22, but long-term creep performance, microstructural evolution, welding characteristics and other properties were not fully defined and assessed. It was also important to improve knowledge of microstructural evolution in order to verify the mechanical behaviour after long-term service. The consortium has produced trial components by industrial process routes for both grades, but the activities have been focused mainly on grade 23, for commercial reasons, and on grade 24 for comparison. New consumables for welding have been developed and tested. Creep test programmes for base material and welded joints, including long-term tests, have been carried out, and some tests will continue beyond the end of the project. The data acquired will also be incorporated in the creep database of the European Creep Collaborative Committee and will be used in the coming assessments for EN standards. The parallel aim of the project was piping integrity assessment under realistic loading conditions by combined thermal and hydraulic system analysis and stress analysis using the data generated during the project. This work has shown that a P23 pipework system will be more durable than an equivalent CMV system providing that good operational practice is maintained, thereby minimising the risks of severe operational transients.