Piping Analysis: A Flexibility Approach

Design for the vertical and horizontal accelerations associated with a seismic event coupled with low allowable loads on equipment are two primary contributors to the current situation. Much effort is currently being expended to address this problem, effort that includes the use of higher damping ratios, consideration of response spectra shifting, and consideration of seismic effects as secondary loading. All of these have the potential of reducing the number of pipe supports, but none of them, with the possible exception of a radically different consideration of damping, appear to offer an optimum solution to the problem of overly rigid piping systems. Regulatory constraints, coupled with a fundamental inability to model a piping system in a way that permits an accurate assessment of its true non-linear behavior, have created an impasse in attempts to develop a new, less restrictive approach to piping analysis. The writers conclude that a focused effort by the nuclear industry, including extensive dynamic testing of large scale piping systems, is called for to address the problem.