RU2263296C1 - Method of determining presence of defects after nondestructive tests - Google Patents

Abstract

FIELD: investigating or analyzing materials.

SUBSTANCE: method comprises determining confidence level of the testing method used from the probability of finding defects, which ranges in a definite intervals of their sizes, determining the number of defects after each nondestructive testing that fall into the definite size interval, removing defects, and calculating the number of defects that fall into the definite interval of sizes.

EFFECT: enhanced reliability.

4 dwg

Description

The proposed invention relates to non-destructive testing (NDT) during the manufacturing, installation and operation of products of modern machine and instrument making, including transport, energy, oil and gas pipelines, vessels, storage, general engineering, etc. The most critical products of modern technology are subjected to repeated non-destructive testing (ultrasound, radiographic, eddy current, etc.), as provided, for example, PNAEG-7-008-86. In this regard, one of the most important tasks in the field of non-destructive flaw detection is what defect remains after the first, second, third and subsequent inspections and how its main indicators can be determined.

The prior art method for non-destructive testing of latent defects in a structure according to A.S. SU 1389422 A1, published on 02.27.1996, IPC 7 G 01 N 3/00.

In accordance with the indicated method, before loading the structure, a moving section of the structure is connected with an elastic element characterized by negative rigidity, comparable in absolute value with the rigidity of the structure under test, but less than that, then the structure is loaded with a variable mechanical load and cause its displacement, the parameters of the structure displacement process are measured and compare them with the same design parameters, the level of defects of which is taken as permissible, on the basis of which they judge residual defects controlled design.

However, this method does not allow to determine the number of defects remaining in the product after several NCs, since in essence only one stage of NCs is implemented in it.

Closest to the proposed technical solution is a method of non-destructive testing of the strength of building structures according to the patent of the Russian Federation RU 2006813 C1, published on 01/30/1994, IPC 7 G 01 N 3/00.

In accordance with the indicated method, the places of possible maximum deformations are determined on the surface of the tested structure, in these places the tested structure is loaded with a mechanical load not exceeding the limit value, the amount of deformation in these places is determined, based on which the residual defective structure is judged. In this case, a mechanical load of a constant value is applied, the test structure is loaded 5-10 times, and the voltage value is taken into account when determining the load value.

However, this method does not allow to determine with high reliability and at low labor costs the number of defects remaining in the product after several NCs.

In this regard, the aim of the present invention is to increase the reliability and simplification of the procedure for determining the number of defects remaining in the product after several NC.

The task can be implemented in three versions.

According to the first variant, the method for determining the residual defectiveness of an article after two or more NCs is to determine the reliability of the applied NC method P _j by the probability of detecting defects lying in certain intervals of their sizes j = 1 ... m, n NCs are carried out, where n ≥2, in this case, after each non-destructive i-th control, the number of defects that fall in a certain interval of their sizes jN _{j, i} is determined, then the defects detected on this NC are healed, and the number of defects falling in a certain interval of z of j remaining in the product after the n-th NC and the corresponding healing of defects is defined as

где

- количество всех выеденных дефектов.

Where

- the number of all defects found.

.According to the second variant, the method for determining the residual defectiveness of the product after two or more NCs is to determine the reliability of the applied NC method P _j by the probability of detecting defects lying in certain intervals of their sizes j = 1 ... m, n NCs are carried out, where n ≥2, in this case, after each non-destructive i-th inspection, the defects detected on this NC are healed, having previously determined the number of defects that fall in a certain interval of their sizes j after the 1st inspection - N _{j, 1} , and the number of defects falling they are in a certain range of sizes j remaining in the product after the n-th NC and the corresponding healing of defects, is defined as

.

а количество дефектов, попадающих в определенный интервал размеров j, остающихся в изделии после n-го НК и соответствующего залечивания дефектов, определяют как

According to the third option, the method for determining the residual defectiveness of the product after two or more NCs is to determine the reliability of the applied NC method P _j and the maximum detectability of defects Pn _j by the probability of detecting defects lying in certain intervals of their sizes j = 1 ... m, spend n NK, where n≥2, and after each non-destructive i-th inspection, the defects detected on this NK are healed, having previously determined the number of defects that fall in a certain interval of their size j after the 1st control a la - N _{j, 1} , determine the number of residual defects not detected by this ND method

and the number of defects falling within a certain range of sizes j remaining in the product after the n-th NC and the corresponding healing of defects is determined as

One of the options for implementing the proposed method is illustrated by the following graphic materials.

Figure 1 shows a histogram of detected defects in the 1st control.

Figure 2 shows a graph with the results of determining residual defects after the 1st, 2nd and 3rd controls.

Figure 3 shows a histogram of detected defects in the 2nd control.

Figure 4 shows a histogram of detected defects in the 3rd control.

The proposed method (in any of its options) is as follows.

To determine the reliability of the applied NC method P _j and the maximum detectability of defects Pn _j (the latter for the third embodiment of the proposed method), the following operations are required:

- a test sample is made containing randomly located defects; this test sample is monitored by the NDT method, which will subsequently be used to diagnose the controlled product

- the test sample is made in the form of a controlled product or its most critical part from the same material and according to the same technology and it contains three groups of defects:

a) defects whose sizes lie in the range from the sizes of defects admissible during operation to the dimensions critical for the product during operation of defects;

b) defects, the sizes of which lie in the range from the sizes admissible in the manufacture of defects to the sizes of defects admissible in operation;

c) defects whose sizes lie in the range from the minimum sizes available for detecting defects to the sizes of defects acceptable during manufacture (it is permissible that the upper boundary of the interval exceed the dimensions of defects acceptable during manufacture).

In this case, the first two types of defects imitate defects of an operational nature, and the third type - of a technological one.

Further, to determine the reliability of the applied NK R _j method, the following steps are required:

- carry out the control of the manufactured test sample by the selected non-destructive testing method, the results of the comparison are compared with real defects embedded in the test sample for each defect size;

- determine the ratio of "the number of detected defects N _OBN to the number of embedded defects N _ZAL ", which characterizes the probability of detection of a given size of defect R _water ;

- according to the results of the control, a probability curve for detecting defects for a given product is constructed using this NDT method depending on the size of the defects, approximating the equation most closely describing the experimental results of the control, and an ideal curve is constructed that characterizes one-hundred-percent detection of defects;

- the reliability of the selected NK method for a given product P _j is judged by how close the experimental curve is to the ideal curve, while:

a) by the part of the probability curve for detecting defects lying between the size of defects admissible during operation and the size of defects critical for the product in the operating mode, judge the reliability of the selected NDT method for the part under study in the area of defects important for the safe operation of the product;

b) according to the part of the curve lying between the size acceptable for manufacturing defects to the size of defects acceptable during operation, the reliability of the selected NDT method for the part under study in the area of defects important for reliability is judged;

c) according to the part of the curve lying between the size of the minimum defects available for detection and the size of defects acceptable in the manufacture, the reliability of the selected ND method for the part under study in the region of defects important for the quality of production is judged.

And to determine the maximum detectability of defects Pn _j , the following actions are required:

- carry out multiple control of the test test sample by the selected NDT method, and each subsequent control is carried out by a new operator, and the number of controls is determined from the condition that the next at least two operators did not find a single new defect compared to their predecessors;

- the characteristics of the defects established by non-destructive testing are compared with the characteristics of the embedded defects, and the results of all the tests performed are successively presented as curves of Depot _k versus the characteristic dimensions of the defect, where Depot _k is the total probability of detecting a defect of the appropriate size by the selected NC method performed by the number of NC operators equal to k, defined as the ratio of the sum of detected at least once as a result of the k-th number of defect checks carried out yes to the number-type embedded in the test specimen of this type of defects;

- the control is terminated if there is a curve whose position on the graph does not change with each subsequent control, and the obtained curve is considered to characterize the ultimate detection of defects by the selected method of NK Pn water;

- an ideal curve is constructed that characterizes the absolute detection of defects, and the maximum detection of defects by the selected NC method for a controlled product is judged by how close the Pn water curve approaches the ideal curve

Further, for the implementation of the proposed method, n corresponding NDs (n≥2) are carried out, after each ND, the number of defects that fall in a certain interval of their sizes jN _{j, i} is determined, after which the defects identified at the next ND are healed. If the residual defectiveness of the product is determined in accordance with the second or third embodiments of the proposed method, then there is no need to determine the number of defects that fall in a certain interval of their sizes j after each NC, it is enough to determine it only after the first NC - N _{j, 1} .

And as a measure of the residual defectiveness of the product after n SC, the number of defects that fall in a certain interval of sizes j remaining in the product after the n-th SC and the corresponding healing of defects is chosen. According to the first embodiment of the proposed method, it is calculated as

А по третьему варианту осуществления предложенного способа сначала определяют не выявленное данным методом НК количество остаточных дефектов как

а количество дефектов, попадающих в определенный интервал размеров j, остающихся в изделии после n-го НК и соответствующего залечивания дефектов, в свою очередь рассчитывается как

According to the second embodiment of the proposed method, it is calculated as

And according to the third embodiment of the proposed method, the amount of residual defects not detected by this ND method is first determined as

and the number of defects falling within a certain range of sizes j remaining in the product after the n-th NC and the corresponding healing of defects, in turn, is calculated as

The possibility of implementing the proposed method (based on the first variant of its implementation) can be illustrated by the following example:

It is required to determine the residual defectiveness of a steel pipeline after three inspections by a non-destructive ultrasonic method using a UD-2-12 flaw detector. The first control is carried out at the manufacturing stage, the second control - before the start of operation, the third - after hydrotesting and trial operation of the pipeline.

The solution of the problem is carried out in 4 stages:

- First, the first control of the pipeline. The control results are presented in the form of a histogram N _{j, 1} from j in figure 1.

- Then, the reliability of the used ND method is determined in the form of the dependence of the probability of detecting a defect P _j on the defect belonging to one or another group of their sizes j (see curve 1 in FIG. 2).

для каждой группы размеров дефектов j в виде кривой 2 на фиг.2.- According to the results of the first NC and the probability of detecting a defect P _j determine the initial defectiveness of the pipeline

for each group of defect sizes j in the form of curve 2 in FIG. 2.

Результаты показаны соответственно в виде кривых 3, 4, 5 на фиг.2.- The residual number of defects after the 1st, 2nd, 3rd and all subsequent controls and healing of all detected defects is determined based on the expression

The results are shown respectively in the form of curves 3, 4, 5 in FIG.

и

, построенные соответственно по результатам 2-го и 3-го контролей.3 and 4 show histograms of defect detection

and

constructed respectively according to the results of the 2nd and 3rd controls.

Similar graphs and histograms also, in principle, can easily be explained and the other two possible options for implementing the proposed method. The only thing that can be said on this subject with respect to these two options is that they do not need to determine the number of defects that fall into a certain interval of their sizes j after each NC, it is enough to determine it only after the first NC - N _{j, 1} .

The proposed method in each individual embodiment of its implementation can significantly increase the reliability and simplify the procedure for determining residual defects in the product after several NCs.

Claims (3)

1. A method for determining the residual defectiveness of an article after two or more non-destructive tests (ND), characterized in that the reliability of the applied ND method P _j is determined by the probability of detecting defects lying in certain intervals of their sizes j = 1 ... m, n nD , where n≥2, and after each non-destructive i-th control, the number of defects that fall in a certain interval of their sizes jN _{j, i} is determined, then the defects detected on this NC are healed, and the number of defects that fall in a certain interval of p sizes j remaining in the product after the n-th NC and the corresponding healing of defects are defined as

2. A method for determining the residual defectiveness of an article after two or more non-destructive tests (ND), characterized in that the reliability of the applied ND method P _j is determined by the probability of detecting defects lying in certain intervals of their sizes j = 1 ... m, n n , where n≥2, in this case, after each non-destructive i-th inspection, the defects detected on this NC are healed, having previously determined the number of defects that fall in a certain interval of their sizes j after the 1st inspection - N _{j, 1} , and the number of defects I get in a certain interval of sizes j remaining in the product after the n-th NC and the corresponding healing of defects, is determined as

3. A method for determining the residual defectiveness of an article after two or more non-destructive tests (ND), characterized in that the reliability of the applied ND method P _j and the maximum detectability of defects Pn _j are determined by the probability of detecting defects lying in certain intervals of their sizes j = 1 .. .m, conduct n NC, where n≥2, and after each non-destructive i-th inspection, the defects identified on this NC are healed, having previously determined the number of defects that fall within a certain interval of their size j after the 1st control a la - N _{j, 1} , determine the number of residual defects not detected by this ND method

and the number of defects falling within a certain range of sizes j remaining in the product after the n-th NC and the corresponding healing of defects is determined as

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