Near-circular defect

By definition, a defect within the pipe is through-wall if the remaining pipe wall thickness at any point is 1 mm or less or if it is expected to be so at the end of the (after repair) extended design life of the pipe. Design of repair then varies based on the defect shape. ISO 24817 has considered three different shapes of defects, which are circular or near circular, axial slots, and circumferential slots. The design for a through-wall defect is experimentally based and requires performance test data. The equations are long and not to be repeated here. As an introduction only, ISO equations for circular or near-circular defects are presented below. 

Through-wall circular or near-circular defect... 

In order to design repair of pipes defected by through-wall circular or near-circular shaped defects, ISO presents Eqn (10.9) ... 

As in the fuse problem, we begin with the explanation of how the presence of defects can increase the local breakdown field. A defect is a local change in the properties of the sample. In an insulator, the defects are conducting parts of the sample. We consider again a spherical defect (circular in two dimensions) and we draw the equipotential surfaces or lines (in two dimensions). In a pure sample, these surfaces or lines are parallel to the electrodes (Fig. 2.12a) but in a sample with one defect they show distortions near it. For a two-dimensional sample, the new equipotential lines are shown in Fig. 2.12(b). One sees that in the vicinity of the defect there is an increase of the field. The sample will break at an applied voltage smaller than the one which is needed to break a pure sample. This is the enhancement effect identical to that of the fuse problem and consequently the curve Vb(p) will exhibit an infinite slope when p goes to zero. 

The 3s band has not been identified in absorption but Allen and Schnepp found a band at the right place in the circular dichroism spectrum. An np series is well known. There are three other series with a near zero quantum defect which can be components of the g g forbidden nd manifold or the nf manifold. The latter corresponds atomically to transitions with AL = 2 and would be weak too. (For reviews see , and... 

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