SCC Life Estimation Based on Cracks Initiated from the Corrosion Pits of Bolting Material SCM435 Used in Steam Turbine

• Published in: JSME International Journal Series B Fluids and Thermal Engineering Vol. 47; no. 2; pp. 316 - 322
• Main Authors: ITOH, Hitomi, OCHI, Mayumi, FUJIWARA, Isao, MOMOO, Takashi
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Tokyo The Japan Society of Mechanical Engineers 01.05.2004; Japan Society of Mechanical Engineers; Japan Science and Technology Agency
• Subjects: Applied sciences; Boilers; Bolting Material; Corrosion Pit; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fracture Toughness; Life Estimation; Stress Corrosion Cracking; Bolting; Service life; Stress corrosion; Stress cracking; Crack depth; Steam boiler; Fracture toughness
• ISSN: 1340-8054; 1347-5371
• DOI: 10.1299/jsmeb.47.316

Life estimation was performed for the stress corrosion cracking (SCC) that occurs in deaerated and wet hot pure steam at the bottoms of the threads of bolts made of SCM435 (equivalent to AISI 4137) used in steam turbine. SCC is believed to occur when corrosion pits are formed and grow to critical size, after which SCC is initiated and cracks propagate until the critical fracture toughness value is reached. Calculations were performed using laboratory and field data. The results showed that, for a 40mm diameter bolt with 0.2% offset strength of 820MPa, the critical crack depth for straight-front cracks was 5.4mm. The SCC life depends on the lubricant used; the SCC life estimated from this value is approximately 70000 hours when graphite is used as a lubricant.