Danger defects

Following the same procedure, a similar double exponential form for the cumulative failure distribution F a) was obtained by Ray and Chakrabarti (1985a) and was finally reduced (fitted) to a Weibull form (Weibull 1951). Later, Duxbury et al. (1986) obtained this generic form (1.25) using Lifshitz argument for the estimate of the size of the most dangerous defect for small disorder (p 1). 

We now consider larger defects but in a small quantity, i.e. we are still in the vicinity of p = 1. In this dilute limit there is no interaction between the defects. The important question is what is the most dangerous defect or, in other words, what is the defect which will introduce the largest enhancement of the current density ... 

The more dangerous defects will be flat defects perpendicular to the current lines. In two dimensions they are lines, but in three dimensions they have the shape of cylinders. Prom the results of Section 1.2.2(a), one can see that the enhancement factor for an elliptic defect (see Fig. 2.4) is k = l/b. Thus a long defect parallel to the current lines b I ) does not affect the current lines, while a long defect perpendicular to the current line b 1) affects them strongly. 

We shall now determine what is the probability of occurrence of a dangerous defect as defined in the preceding section. In the present case of a lattice, it consists in n neighbouring resistors belonging to the same plane perpendicular to the current flow. In d = 2, it is merely a line of n removed bonds and in d = 3, it is an ensemble of n removed bonds forming a hole with approximately the shape of a disc. The current in the immediately adjacent parallel resistor will be in accordance with the enhancement factor in an elliptic defect... 

The probability that n vertical resistors have been removed to form a dangerous defect is... 

In the very dilute limit p —> 1, there is clearly no difference between the two types of percolation. We thus expect, as above, a strong variation of 7f(p) near p = 1. In the dilute limit, when the defects are well separated but their number is not very small, the same argument of dangerous defect that we used in the case of lattice percolation can again be applied. Now L is the ratio between the size of the sample and the diameter of one defect. All the results we established above are valid here. 

We shall now investigate the influence of the sample size. As discussed earlier, it is related to the notion of the most dangerous defect in the sample. In the present case, the most dangerous defect is a cell of the infinite cluster with length in the direction parallel to the current and /max in the perpendicular direction. The total probability of getting a defect of size I is given (using g l) from eqn. 1.23b) by... 

It was found that the failure current If depends not only on the fuse (resistor) concentration p, but also on the size of the sample through InL. The dependence of If on In L was discussed more fully by Li and Duxbury (1987). They also investigated the role of different dangerous defects in this sense, that in their vicinity there is a possibility of strong enhancement of the current. They proposed to define an exponent ip such that If depends on L through (InL) , with an approximate bound for this new exponent ... 

Schedule 1 lists the information to be contained in a report of a thorough examination, for example, name and address identity of equipment date of last thorough examination SWL appropriate interval any dangerous or potentially dangerous defects repairs required date of next examination and test details of the competent person. 

There is a huge amount of data being collected development of algorithms for real-time processing is essential for quick identification of dangerous defects. 

It was also shown, that serious defects were detected, which under normal circumstances could lead to dangerous situations in the following service periods and cannot be detected by the normal conventional testing method. 

There are difficulties of detecting defects in axial canal because of solid sediment layer of 1. 2 mm thick on the canal surface. When using known defectoscope devices a preliminary labor-intensive mechanical treatment of the axial canal surface is needed. The experience of application of different methods of rotor axial canal control in multifunction automatic device ROTOR - K has pointed to the fact that the most effective method is eddy current one [1]. All the dangerous cracks were just detected by the eddy current method, the part of the cracks were not... 

One who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his property is subject to liability for physical harm thereby caused to the ultimate user or consumer, or to his property, if (a) the seller is engaged in the business of selling such a product, and (b) it is expected to and does reach the user or consumer without substantial change in the condition in which it is sold. 

Two comments sought to give content to the terms "defective condition" and "unreasonably dangerous" that appear ia this rule ... 

Differences in rest potential can be about 0.5 V for cell formation with foreign cathodic structures. The danger increases on coated construction components with coating defects of decreasing size on account of the surface rule [Eq. (2-44)], and is limited, for a given soil resistivity p-Mv., not by the grounding resistance of the defect / , but rather by the pore resistance R2 and the polarization resistance of Rp. 

A similar danger of corrosion lies in cell formation in steel-concrete foundations (see Section 4.3). Such steel-concrete cells are today the most frequent cause of the increasing amount of premature damage at defects in the coating of new steel pipelines. The incidence of this type of cell formation is increased by the connection of potential-equalizing conductors in internal gas pipelines and domestic water pipelines [25], as well as by the increased use of reinforcing steel in concrete foundations for grounding electrical installations [26]. 

An essential part of the Engineer Surveyor s role is the detection of defects in plant or of operating practices, which could lead to a dangerous occurrence. This knowledge is part of his experience. Nevertheless he will never disclose to another client or to a third party the sources of his experience in such a way that breach of confidentiality could result. 

Repairs, renewals or alterations to the power press and safety device(s) to remedy defects which are or may become a cause of danger to employed persons (Regulation 6(1)) (see note 2)... 

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