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51317--9486-Life Assessments of Steam Chests and Valve Casings at Four Fossil Fuel Thermal Power Units

Periodic inspections have identified visible cracks on the inner surfaces of steam stop valve and control valve casings at four coal-fired electricity units, each with approximately 50 years of operation. Evaluations were performed to assess the remaining life of those components.

Product Number: 51317--9486-SG
ISBN: 9486 2017 CP
Author: Charles Marks
Publication Date: 2017
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Duke Energy’s Marshall and Allen Steam Stations are 4- and 5-unit stations respectively with current lifetimes of over 50 years each. Periodic inspections of the stop valve and control valve steam chests and valve casings have identified numerous visible cracks on the inner surfaces of those components. Life assessments were performed on the steam chests and valve casings for four of the Marshall and Allen units (Marshall Units 1 and 2 and Allen Units 4 and 5). The assessments incorporated visual examinations phased array ultrasonic test (PAUT) examinations dimensional measurements and FEA stress and crack growth analyses. It was determined that the sizes and growth rates of the cracks that were observed 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.

Key words: Steam chest, stop valve, control valve, creep-fatigue cracking, life assessment, cast 1.25Cr-1.0Mo-0.2V

Duke Energy’s Marshall and Allen Steam Stations are 4- and 5-unit stations respectively with current lifetimes of over 50 years each. Periodic inspections of the stop valve and control valve steam chests and valve casings have identified numerous visible cracks on the inner surfaces of those components. Life assessments were performed on the steam chests and valve casings for four of the Marshall and Allen units (Marshall Units 1 and 2 and Allen Units 4 and 5). The assessments incorporated visual examinations phased array ultrasonic test (PAUT) examinations dimensional measurements and FEA stress and crack growth analyses. It was determined that the sizes and growth rates of the cracks that were observed 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.

Key words: Steam chest, stop valve, control valve, creep-fatigue cracking, life assessment, cast 1.25Cr-1.0Mo-0.2V

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