High Temperature Performance of Creep Strength Enhanced Ferritic Steels Under Steady and Cyclic Operating Conditions

Abstract

High energy components must exhibit reliable long-term performance under cyclic operating conditions. Historically assessment of the performance of these components focused on defining the transients related to hot, warm and cold starts and stops. The complexity and range of cycles in many plants now includes rapid changes in generating output to operating levels of 30 % of rated capacity. In many cases, the desirable levels of low load operation are below the values considered in the original design. EPRI programs have thus been working with utilities to implement monitoring campaigns which record the changes in local pressure, temperature and flow with time at different locations within a system and to undertake analysis to assess the influence of these effects on performance. The present review summarizes EPRI achievements linked to transient effects in modern generating plant, with particular emphasis on the behavior of creep strength enhanced steels. These steels, typically based on 9–12 % Cr, offer significant benefits to the design and fabrication of components in high efficiency fossil fueled plants because, when properly processed, tempered martensitic steels offer an excellent combination of strength and toughness. However, assessment of in-service experience demonstrates that cracking in creep strength enhanced ferritic steel components has occurred relatively early in life. Solutions to prevent cracking are presented.