The U-tubes installed inside the steam generator experience high temperature and pressure as a role of heat transfer. Specially, during the secondary side hydrostatic test which ensures the integrity of steam generator, the U-tube is subjected to high external pressure. The purpose of this paper is to investigate the allowable external pressure of the U-tube in steam generator.

In the ASME B&PV Code Section III [1], the allowable external pressure is determined by the rules of NB-3133. Alternatively, NB-3228 analysis may be applied. In order to determining the allowable external pressure of steam generator tube, the buckling analysis is performed. The analysis consists of the collapse pressure and elastic instability pressure analyses. In this study, these pressures are determined by finite element analysis (FEA) using ANSYS computer program.

The non-linear static analysis is performed with ideally elastic-plastic material properties for the collapse analysis. On the other hand, the elastic instability pressure is calculated by eigenvalue analysis in elastic range. These allowable pressures are found to be 24.1 ksi and 10.5 ksi. Therefore the lower pressure of 24.1 ksi is the allowable external pressure of tube. In addition, the results of analysis are compared with other research [6] and Det Norske Veritas (DNV) offshore standards [11].

In conclusion, the results of buckling analysis are well matched with other research [6] and standard [11]. For steam generator tubes, the collapse pressure is dominant factor in failure. Also, the collapse pressure is largely influenced by the ovality of tube.

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