In one CANDU® nuclear station, 11 outlet feeder pipes have been replaced because of cracking in the bends (9 of them were detected before leaked). The cracked feeder bends, which were made out of SA-106 Grade B material, were 2.5 inches (64 mm) in nominal diameter and with a small bend radius of 3.75 inches (95 mm). In all cases, cracks were primarily axial in orientation and were initiated either on the inside surface along the flanks of the bends or on the outside surface along the extrados of the bends. Root cause analyses indicated that the residual stress played a significant role in these failures. Measured residual stresses data from ex-service and spare feeder bends have been used to identify possible crack locations, to evaluate susceptibility to cracking of various feeder bends and to develop inspection strategies in limited-scope inspection campaigns. This paper documents the numerical prediction of residual stresses in feeder bends and compares these data with field measurements.
Residual Stresses in CANDU Feeder Bends: Comparison of Measurements and Predictions
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Yetisir, M, Khajehpour, S, & Ding, Y. "Residual Stresses in CANDU Feeder Bends: Comparison of Measurements and Predictions." Proceedings of the ASME 2007 Pressure Vessels and Piping Conference. Volume 6: Materials and Fabrication. San Antonio, Texas, USA. July 22–26, 2007. pp. 983-989. ASME. https://doi.org/10.1115/PVP2007-26699
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