Piping elbows with cracks Part 2: Global finite element and experimental plastic loads under opening bending

Abstract

Experimental and finite element (FE) plastic load results of cracked piping elbows under opening in-plane bending are presented and compared with data from similar defect-free components. The elbows used were short-radius components with an outside diameter of 88.9 mm and thickness 5.49 mm. Axial (at the crown) and circumferential (at the intrados) blunt crack-like defects were produced using electric discharge machining (EDM) procedures. Both short (è 218 axial or 2â 468 circumferential) and long (è 758 axial or 2â 1208 circumferential) defects were investigated with three depth±thickness ratios a=t 0:5, 0.75 and 1.0. The FE simulations employed the measured true stress±strain properties for the elbow material and included geometric non-linear behaviour.The results obtained show that piping elbows under opening bending can tolerate substantial defects, with reductions in plastic loads compared with the defect-free component of the order of 15 per cent or less in most cases, except when the defect is through-wall and circumferential and covers an angle 2â 1208 or more, in which case the reduction in plastic load can be as high as 40 per cent.

Piping elbows with cracks Part 1: A parametric study of the influence of crack size on limit loads due to pressure and opening bending

“…These tensile tests, on what was a typical carbon steel piping material, indicated that a clear, perfectly plastic behaviour existed with a`flat region' up to strain levels approaching 2 per cent, beyond which strain hardening occurred (see Fig. 2 of Part 2 [9]). …”

Uncertainty Analysis of Data-Based Models for Estimating Collapse Moments of Wall-Thinned Pipe Bends and Elbows

“…1 [6][7]. Carbon steel bends with an outer diameter (Do) of 400mm and a nominal thickness (tnom ) of 20mm were used.…”

Net-section limit moments and approximate J estimates for circumferential cracks at the interface between elbows and pipes

“…These parameter sets are believed to cover the practically relevant range of elbows in the power generating industry. The length of the attached straight pipe is chosen to be ten times the pipe mean radius, L ¼ 10r, which is sufficiently long to avoid end effects due to the applied loading [16][17][18][19][20][21]. Both circumferential part-through surface and through-wall cracks were considered.…”

“…[11][12][13][14]). For cracked elbows, several researchers performed both experimental and numerical works to investigate the effect of cracks on plastic limit loads [15][16][17][18][19]. The authors also proposed closed-form approximations of plastic limit loads for circumferential cracked elbows under in-plane bending, via small strain three-dimensional (3-D) finite element (FE) limit analyses using elasticperfectly plastic materials [20,21].…”