Life Assessments of Steam Chests and Valve Casings at Four Fossil Fuel Thermal Power Units

摘要

Periodic inspections have identified numerous visible cracks on the inner surfaces of steam stop valve and control valve casings at four coal-fired electricity generation units, each with approximately 50 years of operation. Evaluations were performed in recent years to assess the remaining life of those components. The assessments incorporated visual examinations, phased-array ultrasonic test (PAUT) examinations, dimensional measurements for creep analyses, and stress and crack growth analyses using finite-element analysis (FEA). It was determined that the sizes and growth rates of the observed cracks in all of the inspected units were such that there is substantial margin available before the valve casings would be expected to reach life-limiting levels of creep, cracking, or fatigue.