Impression creep testing for evaluation of grade 22 ex-service hot reheat piping seam weld

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.

Keywords

• impression creep
• seam weld
• small sample testing
• crmo steels
• remaining life assessment