Considerations of the Restraint Introduced by Piping Support Friction in a Comprehensive ASME B31.3 Analysis

This paper discusses the prescribed requirements contained within the ASME B31.3 Process Piping Code that specifically address the need to recognize the restraint introduced by piping support friction. The requirement for the design of sliding supports (pipe shoes) and brackets to resist the forces due to friction in addition to the loads induced by bearing is also reviewed and discussed. Questions surrounding the inclusion of the effects of utilizing the maximum coefficients of static friction and the impact of these values on equipment nozzle loadings are explored in light of the qualitative guidelines contained within WRC Bulletin 449. The restraint provided by support friction is approached through the mathematical treatment of extrema with respect to calculated nozzle loads. The calculated nozzle loads then become based upon the analyst’s choice of the largest referenced coefficients of static friction (in most cases) between the two interfacing materials under consideration. It is highly improbable that the choice of the maximum coefficients of friction at each support will exist, but rather, it is physically impossible for this “worst case” condition to occur. Recommendations for the proper treatment of the potential restraint induced by piping support friction in a Code piping analysis are tendered.