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

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 (theta = 21 degrees axial or 2 beta = 46 degrees circumferential) and long (theta = 75 degrees axial or 2 beta = 120 degrees 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 2 beta = 120 degrees or more, in which case the reduction in plastic load can be as high as 40 per cent.