Failure Behavior of Elbows With Local Wall Thinning

Abstract

Wall thinning defect due to corrosion is one of major aging phenomena in carbon steel pipes in most plant industries, and it results in reducing load carrying capacity of the piping components. A failure test system was set up for real scale elbows containing various simulated wall thinning defects, and monotonic in-plane bending tests were performed under internal pressure to find out the failure behavior of them. The failure behavior of wall-thinned elbows was characterized by the circumferential angle of thinned region and the loading conditions to the piping system.

Effect of local wall thinning on shakedown regimes of pressurized elbows subjected to cyclic in-plane and out-of-plane bending

“…As mentioned earlier, Lee et al [15] conducted real scale tests to investigate the failure behavior of pressurized carbon steel elbows, with manufactured wall thinning at the intrados/extrados, subjected to monotonic IPC and IPO bending till collapse. Figure 3(a) illustrates a schematic of Lee et al [15] experimental setup in which the elbow specimen is welded to two identical straight pipes of the same elbow material and pipe geometry. The lower pipe is pivoted to a fixed support while the upper pipe is pivoted to a sliding support on which controlled displacement δ is applied to attain elbow IPC/IPO bending modes.…”

“…Table 1 lists the major geometric dimensions of the elbow assembly. The elbow material as prescribed by Lee et al [15] is ASTM A234 Gr-WPB with mechanical properties listed in Table 2.…”

“…4 are employed in the nonlinear FE analyses utilized to predict the global F δ − response curves for comparison with the experimentally observed data of Lee at al. [15]. The general purpose nonlinear FE software ABAQUS [39] is utilized for simulation of Lee et al [15] tests.…”

“…[15]. The general purpose nonlinear FE software ABAQUS [39] is utilized for simulation of Lee et al [15] tests. Due to full symmetry under both IPC and IPO bending loads, only half geometric model is…”

“…Finer mesh is adopted at the elbow whereas coarser mesh is adopted upon moving away along the straight pipes. Several mesh convergence checks were performed until the generated load-deflection curves yielded comparable F-δ responses to Lee et al [15] observed test results. At the thinned areas, shell thickness was gradually reduced till the prescribed minimum thickness ( p t ) is approached at the elbow midplane following a circular arc geometric thinning pattern as illustrated within Fig.…”