Abstract
U.S. electric power production is significantly dependent on the operation of coal-fired steam generation units and a large majority of these units are reaching ages over 50+ years with concerns for operating component integrity and remaining life. This paper discusses a small sample testing technique (impression creep) that was used to estimate the remaining life of a hot reheat seam welded piping system that saw about 322,000 hours of operation at nominally 4170 kPa (605psig) and 538°C (1000°F) steam conditions. Two different life assessments using experimental impression creep data are discussed and findings compared to a previous preliminary study of the same piping system using operational data, reported measured piping thickness values (from UT measurements), and published creep rupture data. Impression creep tests were conducted in unaffected base metal, weld metal and the heat-affected zone. Impression creep rates of the various zones showed no creep mismatch. Minimal creep mismatch, proper design, fabrication and operation, combined with proper metallurgy have successfully demonstrated that even low-alloy seam welds can operate 300,000+ hours and still exhibit useful remaining life.
Highlights
The world’s first commercial supercritical coal fired power plant was commissioned in 1957 in Philo, Ohio
The impression creep test material was from samples removed from a portion of the HRH system with nominal dimensions of 560mm (22 inch) OD and 28.6mm (1.125 inch) wall thickness
Hardness tests conducted on two other samples not included in this paper showed similar results
Summary
The world’s first commercial supercritical coal fired power plant was commissioned in 1957 in Philo, Ohio. This engineering accomplishment resulted in a significant increase in thermal efficiency in power generation [1]. U.S electric power production remains significantly dependent on the operation of a number of these steam generation units, including coal-fired ones that are exceeding 300,000 hours of operation. In 2017, about 30% of the United States electricity was generated from coal sources [2,3] With many of these aging units continuing to operate, there is a need for improved component integrity and life management strategies, including review of prior assessments in high energy piping and other critical components. The general movement to cleaner energy sources has further complicated life management strategies as these aging assets are expected to cycle and operate outside their intended baseload operation
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