7 - Boiler steels, damage mechanisms, inspection and life assessment

Abstract

This chapter covers the general introduction to the materials used for power plant boilers and a brief history of their development. Materials ageing and component failure mechanisms are then outlined. This is followed by a somewhat more detailed coverage of the microstructural aspects of 9–12 %Cr martensitic steels, the formation of various precipitates during their production and operation at high temperature and their role in the creep strengthening of these alloys. As the use of high Cr steels is now approaching the mid-life stage, cracking and failure has been experienced in many plants worldwide. However, it has been realised that inspection and early stage creep damage detection in these steels is somewhat more challenging than the traditional low alloy steels and in view of this, inspection and monitoring techniques recently developed or being developed for the high Cr martensitic steels have been discussed.