A heat exchanger tubesheet experienced cracks in the ligaments between tube holes. This paper describes the analyses that were performed in order to determine the cause of the crack. The first analysis examined the residual stresses in the tubesheet caused by the tube-rolling. It showed that the residual stresses caused by a typical rolling operation would be negligible. The second analysis examined the steady-state operating condition. It indicated that a tensile stress field existed on the surface of the tubesheet — a potential crack propagation driving force. The third analysis examined a thermal transient caused by a process upset. This transient created high peak stress intensities. However, a fatigue analysis indicated that the stress intensities were inadequate to initiate a crack in the low-cycle fatigue regime. The results of these analyses pinpoint the locations of the cracks accurately, and indicated that while a crack propagation mechanism existed, a crack initiation mechanism did not. Therefore, it was concluded that the crack may have been caused in the manufacturing process.

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