Relaxed Hanger Spans for Non-Critical Piping

Piping systems are normally used to transport air, gases, steam, water, and other fluids. Piping systems in power plants, petro-chemical, and other industrial facilities that carry non-hazardous fluids like air, water, etc. with no significant pressures at moderate temperatures can be considered as non-critical. Codes such as ASME B31.1 provide suggested dead weight spans for the placement of supports. In this paper, relaxed hanger spans are computed for non-safety related piping systems taking in to consideration the maximum bending stress, maximum deflection or pipe sag, and bearing stresses due to dead weight for pipe sizes ranging from 1” to 42” diameter. For situations in which large diameter pipes are directly sitting on steel with a line contact, bearing stresses are computed using finite element analysis as well as simple formulas. A comparison of relaxed hanger spans with B31.1 suggested spans is presented. Significant benefits in lowering the cost due to reduced number of dead weight supports, and the associated savings due to reduction in materials, fabrication, and installation can be derived by using the relaxed spans. These relaxed hanger spans were utilized over the past nine years on a variety of non-safety related piping systems. Experience with more than a dozen power projects of Pulverized coal (PC), Cogen, Simple cycle, and Combined cycle types indicates that the piping systems, which used relaxed hanger spans, are operating normally and satisfactorily without any problems.