Effects of Pipe-System Restraint on COD Calculations of Axial Loaded Pipes forLBB Applications – Finite Element Round Robin Results

摘要

Typical LBB analyses require calculations of the crack-opening displacement (COD) for pipe under bending andaxial tension loads. These models all assume that the pressure loads are essentially modeled as an end-capped pressure vessel.There are natural rotations that occur due to the presence of the crack that are restrained in a real pipe system by the presenceof nozzles, elbows, pipe hangers, and other boundary conditions. Other axial tension loads also introduce the rotationaleffects on the crack-opening displacement that will be restrained by the pipe-system boundary conditions. Earlier sensitivitystudies on this restraint of the pipe rotations showed that the crack-opening displacement could be significantly reduced bythe pipe system boundary conditions. This effect could be highly detrimental to achieving LBB conditions.This paper describes a round-robin effort conducted as part of the on-going Battelle Integrity of Nuclear Piping(BINP) Program to characterize the piping system restraint effects on the crack-opening displacement for different pipediameters, crack lengths, pipe radius-to-thickness ratios, and distances from the crack plane to the restraining boundarylocation (both symmetric and non-symmetric restraint lengths). These efforts are leading to an analytical correction to theexisting crack-opening displacement analyses for improved LBB analyses.