Many leakage troubles were reported in petroleum and petrochemical refineries for bolted flanged connections in elevated temperature service due to the effect of differential thermal expansion in flanges, bolts, gasket, and so on as an assembly. The leakages were found especially in shut down condition for petroleum refineries and chemical plants, even if the weather seal (rain cover) was installed to prevent the flange assembly from rapid cooling by wind or rain. On the other hand, the leakage mechanism of the bolted flanged connections with weather seal under the condition of wind flow is not still clearly understood. Therefore, the leakage behavior on bolted flanged connections is investigated using the latest computerized fluid dynamics (CFD) and the structural thermal analysis with nonlinear material properties in flange and gasket (FEM: Finite Element Method). The actual environmental effect such as wind is modeled by CFD, and the plasticity is also taken into account by the nonlinear material properties in flange and gasket by FEM. The case studies are performed for 6”, 12” and 18” for Class 2,500 with ring joint gasket. In addition, the two temperature and pressure cycles including first start-up, normal operation, shut-down, and the consequent start-up, normal operation, emergency shut-down conditions are considered. Thus, the leakage phenomena are able to evaluate, and the guideline is proposed for maintenance.

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