Prediction of creep failure of ۱۴CrMo۳ superheater tubes based on FFS Assessments

This investigation assessed the fitness-for-service of ۱۴Cr Mo۳ steel seamless tubes extracted from a ۳۲۰ MW power plant superheater. The study revealed a multifaceted degradation mechanism impacting tube integrity. Analysis of the flue gas-facing side indicated fuel ash corrosion, evidenced by the presence of vanadium and sulfur deposits and the formation of low melting point salts. This corrosion compromised the protective oxide layer, resulting in wall thickness reduction. Concurrently, the steam side exhibited iron oxide layer formation and evidence of water presence due to steam drum malfunction, creating insulated zones and localized hot spots. These conditions fostered creep microvoid formation and carbide spheroidization. An ۱۸% thickness reduction significantly elevated hoop stresses, diminishing remaining creep life. Applying Larson-Miller criteria and API ۵۷۹-۱/ASME FFS-۱ guidelines, coupled with finite element analysis, demonstrated the sensitivity of tube lifespan to temperature fluctuations. A mere ۵۰°C increase drastically reduced the predicted service life, highlighting the criticality of maintaining optimal operating conditions to ensure superheater reliability.

Keywords:

super heater tube , failure analysis , fitness-for-service assessment , creep