Improved Analysis of External Loads on Flanged Joints

Abstract

External loads on bolted flanged joints must be assessed in order to be in compliance with ASME and other international pressure vessel and piping codes. However, in the case of the ASME B31.3 piping code or ASME VIII, Division 1 pressure vessel code, there is not specific guidance on how to assess these loads. This has created a situation where piping designers have employed a variety of methods, ranging from very conservative to possibly non-conservative. A review of historical joint external load experiments is made in this paper, which highlights the relatively low risk of joint leakage due to external loads. In addition, an improved method of assessing the acceptability of external loads for any given joint is introduced and compared to both test results and existing assessment methods. The method presented is based on probability of leakage for standard piping joints using the method outlined in Appendix O of ASME PCC-1 [1]. This allows, in some cases, a much higher acceptable load than typically employed when using traditional methods such as the Equivalent Pressure method. By allowing higher external loads, it is possible to reduce the footprint of a process unit, which saves money, while maintaining safety.