Comparison of the stress intensity factor for a longitudinal crack in an elliptical base gas pipe, using FEM vs. DCT methods

Abstract

While several theoretical and experimental studies for cracks in piping exist, most pertain to pipelines, equipment, or fittings under pressure conditions or under stress corrosion conditions at welding. Element finite Method models have occasionally supplemented experimental methods, to investigate such operational fails. In this approach we explore technical options to comprehensively understand crack propagations, by first, evaluating the Stress Intensity Factor (KI) using ANSYS Parametric design language then, comparing with the Displacement Correlation Technique, for an elliptical base gas piping (20″APL Gr. B) suffering a longitudinal welding-induced crack, under a compression of 1.86 MPa. The KIvalue for an Electric Resistance Welding crack was calculated for the two-dimensional plane, for a quarter-length of propagated crack along the elliptical front. The KI value estimates are 0.94x(10)−3 MPam from ANSYS Parametric design language vs. 0.70x(10)−2 MPamfrom DCT the two methods are close less than 1. These results were compared with the theorical stress intensity factor for elliptical cracks by Broek11 Broek, D. (1984). Elementary engineering fracture mehcanics . The Hague: Martinus Nijhoff Publishers. David called elementary engineering fracture mechanics where the values were 0.5x(10)−1 MPam. We found that the proposed FEM method for estimating (KI)is the approach that is closest to the theoretical value.

Keywords

• Piping
• Finite Element Method (FEM)
• Stress intensity factor
• Cracks propagation
• Displacement Correlation Technique (DCT)