Quantification of the uncertainty in stress index B2 for pipe bends subjected to out-of-plane bending

Abstract

Over the last decade, the requirement for moving from a deterministic design to a more rational reliability-based load and resistance factor design (LRFD) guideline has been emphasised in the area of pressure vessel and piping. For reliability-based code calibration of pipe bends, a quantification of the uncertainty in the primary stress indices (for pressure B1 and for bending B2) is the first significant task. This paper presents a Monte Carlo simulation-based probabilistic characterisation of B2 for Class 2 and 3 Type 304 stainless steel thin pipes with a 90° long radius bend, subjected to out-of-plane flexure. The ASME B&PV Code, Section III equations (NC 3673.2 and ND 3673.2) to calculate B2 are proposed to be revised using a random variable (K), for which detailed statistics (including the cumulative distribution function) are provided. An alternative equation, based on linear regression analysis, is also suggested which provides a better fit for the B2 statistics. These information can be used suitably to formulate an LRFD equation for pipe bends.