Исследование выявляемости поверхностных плоскостных дефектов ультразвуковым методом с применением волн Рэлея

The issues of detecting operational surface planar flaws by the ultrasonic non-destructive testing method with the use of Rayleigh surface waves generated by an electromagnetic-acoustic transducer are considered. The paper presents experimental studies of planar defects detection, simulated by an artificial reflector of the "notch" type with different width, depth and angle of inclination. The dependences of the signal amplitude on the listed parameters are constructed and their character was estimated. The optimal amplitude models for constructing the probability of detection curves (PoD) have been determined. A conclusion is made about the minimum dimensions of an operational planar flaw detected by the considering method with a probability of 90%, taking into account the confidence interval of 95%.

Study on the Effect of Axial Flaw Length on Limit Bending Load of Wall Thinned Straight Pipes by Large Strain Finite Element Analyses

In this paper, we examined the effect of axial flaw length δz (Fig. 1) on limit bending load Mc of wall-thinned straight pipes by large strain finite element analysis (FEA). In the past, Han et al. [1] studied the effect of axial flaw length δz on limit bending load Mc of wall-thinned straight pipes by limit-load analyses. Han et al.’s [1] results indicated the trend which the Mc monotonically decreased with the increase in δz. If this finding is accepted, the Mc for a crack is larger than that for a non-planar flaw (wall thinning), and as a result, using the crack model for a non-planar flaw would be non-conservative. In contrast, Tsuji and Meshii [2] demonstrated by their tests that the Mc showed the maximum for a small δz. They estimated that this inconsistency was mainly due to the fact that Han et al. [1] and other researchers always assumed the fracture mode as the collapse, but the cracking was observed in Tsuji’s [2] experiment for small δz. Therefore in this work, we examined the effect of axial flaw length δz on limit bending load Mc of wall-thinned straight pipes by large strain FEA and applying Domain Collapse Criterion (DCC) [3] (which can predict fracture mode and the Mc accurately) to FEA results. In concrete, we attempted to reproduce Tsuji and Meshii’s experimental results [2] by FEA that the Mc showed the maximum for a small δz. In addition, we tried to understand the reason why limit-load analysis failed to predict this tendency. The results showed that large strain FEA with DCC [3] reproduced the Mc-δz relationship observed in the experiments. The inconsistency of Mc-δz relationship between Tsuji and Meshii’s experiment [2] and Han et al.’s limit-load analysis [1] and others analysis was estimated on due to the limit-load analysis failed to predict the failure for the flaw with a small δz, in which the failure mode is governed by the local stress (cracking) and not by the plastic deformation in a large volume (collapse).

Influence of Circumferential Flaw Length on Internal Burst Pressure of a Wall-Thinned Pipe

The effect of the circumferential angle of a flaw θ on the internal burst pressure pf of pipes with artificial wall-thinned flaws is examined. When evaluating pf of wall-thinned straight pipes, the effect of θ has been conventionally not regarded as important. Therefore, a burst pressure equation for an axial crack inside a cylinder (Fig. 1, left), such as Kiefner’s equation [1] is widely used [2], [3]. However, it should be noted that there exist the following implicit assumptions when applying the equation for planar flaws to non-planar flaws. 1) The fracture mode of a non-planar flaw under consideration is identical with that of the crack. 2) The effect of θ, which is not considered for an axial crack on pf, is small or negligible. However, from the systematic burst test results of carbon pipes with artificial wall-thinned flaws, Meshii [4] showed that these implicit assumptions may not be correct. On the other hand, the significance of the effect of the fracture mode on pf and the condition for θ to affect pf are not clear. Therefore, in this paper, Meshii’s experimental results are evaluated in farther detail. The purpose of the evaluation was set to clarify the effect of θ on pf. Specifically, the significance of flaw configuration (axial length δz and wall-thinning ratio t1/t) was studied in relation to θ and pf. In addition, a simulation of the effect by a Finite Element Analysis (FEA) was attempted. From the experimental results, θ tended to affect pf in cases with large δz, and t1/t also was correlated to a decrease in pf with the increase of θ. These tendencies were successfully simulated by the elastic-plastic FEA. This effect means the burst pressure predicted for a crack with identical ligament thickness decreases with the increase of θ, so that the effect by θ on pf should not be ignored.

Proposal of Limit Moment Equation Applicable to Planar/Non-Planar Flaw in Wall Thinned Pipes Under Bending

In this paper, limit bending moment equation applicable to all types of planar and non-planar flaw in wall thinned straight pipes under bending was proposed. An idea to rationally classify planar/non-planar flaw in wall thinned pipes was proposed, based on the experimental observation focused on the fracture mode. The results point out the importance to distinguish axially and circumferentially long flaws in wall thinned pipes.

Proposal of a Guideline to Classify Planar/Non-Planar Flaw in Wall Thinned Straight Pipes Under Bending Load

In this paper, an idea to rationally classify planar/non-planar flaw in wall thinned straight pipes under bending load was proposed, based on the fracture mode (cracking/non-cracking) observed in experiments. This cracking phenomenon was correlated with the aspect ratio of the flaw planar configuration. Finally, a guideline to classify this planar/ non-planar flaw based on flaw aspect ratio was proposed.

Proposal of an Internal Burst Pressure Equation Applicable to Planar/Non-Planar Flaw in Wall Thinned Pipes

In this paper, an internal burst pressure equation applicable to all types of planar and non-planar flaw in wall thinned straight pipes was proposed. An idea to rationally classify planar/non-planar flaw in wall thinned pipes was proposed, based on the experimental observation focused on the fracture mode. The results point out the importance to distinguish axially and circumferentially long flaws in wall thinned pipes.