Load Carrying Capacities of Small-Diameter Pipe Bends under Internal Pressure: Analytical and Computational Predictions

Abstract of the technical conference paper:
2024 Pressure Vessels and Piping Conference (PVP 2024)
July 28-August 2, 2024
Bellevue, WA, US

Prepared by:
N. Robinson and X. Wang
Carleton University

B. Wasiluk
Canadian Nuclear Safety Commission

Abstract:

The performance and embedded conservatism of common modeling approaches used for predicting load carrying capacities were evaluated for small-diameter pipe bends typically found in CANDU reactors. Comprehensive analyses were conducted using both an analytical approach and detailed finite element modelling with the commercial code ABAQUS. Small diameter pipe bends, with and without local wall thinning, under loading by internal pressure were investigated. The adopted modelling approach incorporated variability in pipe bend geometry and the characterization of material properties.

The results obtained indicate that load carrying capacities of small-diameter pipe bends, either with or without local wall thinning but characterized by uniform wall thickness and single parameter material strength, are conservatively predicted with analytical models in principle based on the limit load approach. However, detailed finite element modelling is necessary for obtaining more accurate predictions of plastic instability pressure for pipe bends with local wall thinning.

The reported investigation provides technical insights into the modelling approaches presently used for predicting load carrying capacities of small-diameter pipe bends under internal pressure loading; in addition, it has explored embedded conservatism while recognizing the existence of involved uncertainties. The results obtained emphasize the importance of detailed characterization of pipe bend thickness and material strength in such engineering predictions.

This work has been performed under Canadian Nuclear Safety Commission (CNSC) Research and Support (R&S) project R765.1. The insights obtained may be used to further assess embedded conservatism in fit for service evaluations of CANDU outlet feeders experiencing wall thinning due to Flow Accelerated Corrosion (FAC). In addition, supplementary information informs the activities related to lowering the minimum required thickness below 75% of a straight pipe thickness by Article NB-3640 of Section III of the ASME B&PV Code for design pressure.

To obtain a copy of the abstract’s document, please contact us at cnsc.info.ccsn@cnsc-ccsn.gc.ca or call 613-995-5894 or 1-800-668-5284 (in Canada). When contacting us, please provide the title and date of the abstract.