Statistical characterisation of B2 for nuclear pipe bends: In-plane closing moment

Abstract

In recent years, the necessity of reliability-based design has received significant attention from researchers working in the area of pressure vessels and nuclear piping. Preliminary guidelines have been formulated for the reliability-based design of straight pipes using the load and resistance factor design (LRFD) format. In order to formulate similar LRFD design equations for pipe bends and elbows, the first step is a statistical characterisation of the stress indices B1 and B2, which play a significant role for the stress analysis of bend geometry. This paper focuses on the statistical characterisation of B2, which arises due to fabrication/geometric uncertainties, for a thin stainless steel pipe with a 90° bend, subjected to in-plane closing moment. Based on Monte Carlo simulation and nonlinear finite element analyses, the code-based expression for B2 is revised with a random variable K replacing the constant numerator. The statistics for K are provided for different pipe nominal dimensions. The overall mean value of K indicates that the existing code provision gives a conservative estimate of plastic collapse moment for pipe bends subjected to in-plane closing bending moments.