Damageability of the Metal of Combined Cycle Plant Heat Recovery Steam Generators and the Service Properties of Advanced Lifetime-Governing Metals Used in Them

A sampling analysis of the results from examining the metal of 25 heat recovery steam generators (HRSGs) used as part of combined cycle plants (CCPs) installed at 12 power plants in Russia is carried out. In-service examination of the HRSG metal is as a rule carried out during the equipment overhaul. The metal defects revealed during the steam generator diagnostic activities are in most frequent cases damages in weld joints, some of which were left in the steam generator manufacturing or installation stage, while the other ones emerged during the operation. Operational defects include, among others, the thinning of component walls. Factors causing various kinds of metal defects are briefly analyzed. Advanced steels developed outside of Russia are used in some heat recovery steam generators as the structural material for manufacturing the critical components. Assessing the quality of these steels and the stability of their service properties is a top-priority objective pursued in analyzing the HRSG metal state. In the course of activities carried out at the VTI on studying full-scale welded billets made of grade WB36 steel used to manufacture the drums, it has been confirmed that the main service characteristics of this steel comply with the applicable regulatory requirements, and that the steel has satisfactory properties in terms of resistance to low-cycle and brittle fracture. This made it possible to increase the fleet service life of high-pressure drums (HPDs) made of this steel. For high-chromium steels of grades P91 and Di82, the results of representative tests for long-term strength have been generalized and processed, which opens the possibility in principle to estimate the current state of metal and predict the lifetime characteristics of the critical components of heat recovery steam generators.