Life-assessment technology for fossil power plants

Abstract

During the last decade, construction of new fossil power plants has come to a virtual halt in the United States. The main factors responsible for this situation are: (1) industry perception of the existence of sufficient reserve margins, (2) uncertainty in forecasting load growth, (3) cost of borrowing for new plant construction, (4) siting and licensing problems for new plants, and (5) the applicability of more stringent environmental standards for new plants. Unfortunately, by the year 2000 it is estimated that nearly 20% of all the fossil units will be more than 40 years old, and almost 44% will be more than 30 years old. Based on historical trends, nearly half of all fossil plants have been retired before their fortieth year and three quarters before serving 50 years. In the future this trend is unlikely because of the shrinking reserve margins and the long lead time for new capacity addition. If the life of these aging plants can be extended by 20-30 years, utilities can have a viable low-cost alternative to building new plants while at the same time circumventing some of the regulatory, siting and licensing constraints. In view of this, plant life extension has become an integral part of the planning strategy for many US utilities. A critical component of the Electric Power Research Institute's (EPRI) efforts in formulating life extension strategies for fossil power plants is the development of techniques to assess the current condition of high-temperature components. These techniques are necessary not only for assessment of the remaining life, but also for avoiding catastrophic failures and forced outages, for setting up inspection intervals and for optimizing the operating procedures. The components that are being addressed at present are boiler pressure parts, steam pipes and steam turbine rotors. This paper will provide a brief overview of current concerns and areas of research where significant progress has been made to address these concerns from a phenomenological point of view.

Effect of Austenite-to-Ferrite Phase Transformation at Grain Boundaries on PWHT Cracking Susceptibility in CGHAZ of T23 Steel

“…However, in the case of T23 material, PWHT cracking (reheat cracking) has been reported in the process of post-weld heat treatment (PWHT) to mitigate the residual stress in the weld metal [8][9][10][11][12][13][14][15][16]. Therefore, much research has been conducted to analyze the cause of the formation of reheat cracks in 2.25Cr-1.6W steel.…”

Effect of Austenite-to-Ferrite Phase Transformation at Grain Boundaries on PWHT Cracking Susceptibility in CGHAZ of T23 Steel

“…However, in the case of T23 material, PWHT cracking (reheat cracking) has been reported in the process of post-weld heat treatment (PWHT) to mitigate the residual stress in the weld metal [8][9][10][11][12][13][14][15][16]. Therefore, much research has been conducted to analyze the cause of formation of reheat cracks in 2.25Cr-1.6W steel.…”

Remaining life assessment for boiler tubes affected by combined effect of wall thinning and overheating

“…Carbon steel, however, brings new requirements as overheating and creep as well as hydrogen embrittlement should be considered as an additional and sometimes major damage mechanisms. It is generally recognized that creep may initiate in carbon steels in temperatures over 420-440 °C, which is well within the range in water-wall boiler tubes [1]. For that reason, any preventive maintenance procedures have to consider overheating as a possible cause of failure.…”