Advanced Elastic Follow-up Factor for Elbow Piping of Carbon Steel

Abstract

A piping system subjected to earthquake possibly deforms plastically in design analysis because design seismic ground motions have been increased recent years. Though simplified elastic plastic analysis using elastic follow-up factor is standardized in design code to evaluate elastic plastic strain based on elastic analysis results for fatigue evaluation, elastic follow-up factor is conservative for piping systems. In this research, static elastic and elastic plastic analyses for elbow pipe connected to two straight pipes were performed with a view of streamlining the elastic follow-up factor. Forced displacements were applied to the analysis models so that four times stress of yield stress was generated at elbow pipe. In these analyses, outer diameter, thickness, curvature radius of elbow, and length of straight pipe were changed to verify the effect of pipe size on elastic follow-up factor. From the analysis results, it was clarified that elastic follow-up factors are varied depending on pipe size. Therefore, coefficient factor h’ was defined newly to represent pipe size, and it was indicated that elastic follow-up factor can be expressed as a function of coefficient h’. Mean line and upper envelope line were proposed to predict elastic follow-up factor as a function of coefficient h’.