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

Abstract

Finite element analyses of cracked short-radius piping elbows are reported. Both axial and circumferential cracks, centred about the bend crown or intrados respectively, are considered. The defects are internal, with depth±thickness ratios a=t in the range 0:25 < a=t < 1:0. Since the aim is to assess limit loads, the analysis assumes elastic±perfectly plastic material behaviour with no geometric non-linearities. The loadings considered are (a) opening bending moment, (b) internal pressure and (c) combined loading of steady pressure, set at the design value of the pipe elbow, with a superimposed monotonically increasing opening bending moment.For each type of loading, the general component behaviour, by consideration of the global deformation with increasing load, is reported. Limit load values for each case are presented and the relative reductions in load-carrying capacity, compared with that predicted for a defect free elbow of the same material and dimensions, are given. NOTATION a crack depth A, n constants bradius ratio R=r m D o pipe outside diameter h bend characteristic tR=r 2 m K r measure of proximity to failure by linear elastic fracture mechanics L r measure of proximity to plastic limit load failure m normalized moment for an uncracked pipe M=4S y r 2 m t M moment M L limit moment of elbow M S limit moment of straight pipe p normalized pressure for an uncracked pipe Pr m =S y t P pressure P d design pressure P L limit pressure for an elbow P S limit pressure for a straight pipe r m pipe mean radius r ml

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].…”

Plastic loads of elbows with local wall thinning under in-plane bending

“…1a). Introduction of the attached straight pipe is to minimize the end effect due to the applied loading (Roberston et al 2005;Yahiaoui et al 2000;, and the length of the attached straight pipe, L, was chosen to be sufficiently long (five times the bend radius, L = 5R) in the present work. The objective of this work is to quantify the effect of local wall thinning on plastic behavior and plastic loads of elbows.…”