Pressure design of straight pipe under external pressure is performed in accordance with ASME B31.3 and Section VIII, Division 1 of Boiler and Pressure Vessel Code. And design length of straight pipe shall be defined in accordance with UG-28 and UG-29.

However, there is no specific guideline about the design length which includes branch connection in piping system. Even though the branch connection is not a stiffening component, calculated result shows that increased design length can be considered for piping including the branch connection compared to straight pipe.

This paper presents the study result that shows a tendency depending on several geometry parameters (e.g. Ratio of a diameter of header pipe to a thickness of header pipe.) using elastic buckling analysis performed in accordance with ASME Boiler and Pressure Vessel Code, Section VIII, Division 2. In addition to the result, this paper compares the design length of straight pipe with that of piping system including the branch connection under about the same eigenvalue condition which is called as a “Buckling load multiplier”. Shell element is enough to check the tendency and compare various results by comparison with solid model, because the result is related to overall structural integrity rather than local stress. Shell element is used in the elastic buckling analysis.

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