RU2254562C2 - Method of determining presence of initial and residual defects - Google Patents

Abstract

FIELD: nondestructive testing .

SUBSTANCE: method comprises manufacturing test-specimen for determining characteristics of the nondestructive testing of the cavities in the article and nondestructive testing of the specimen.

EFFECT: improved method.

3 cl, 6 dwg, 1 tbl

Description

The invention relates to the field of non-destructive testing (hereinafter referred to as NC) of discontinuities, inhomogeneities and other defects in the material of a product or a group of products (parts, structural elements, etc.), including ultrasonic, eddy current, radiographic and other methods of NC. The invention can be used in assessing the quality, reliability and safety of a product based on the results of a tax code, assessing the suitability of the means and methods of a tax code, the adequacy of the qualifications of the operators of a tax code, and organizing product control during operation and / or manufacture.

In accordance with existing practice in modern technology, NK of critical products is carried out after manufacture, before operation and during operation. At the same time, it is assumed that as a result of the NC, all defects that are available for detection by this control method are detected. All discontinuities, inhomogeneities, and the like anomalies of the metal, if they exceed the permissible sizes, are classified as defects and are eliminated by repair. It is believed that after repair and repair of defects, there are no other defects in the product (see, for example, “Equipment and pipelines of nuclear power plants. Welded joints and surfacing, Control rules”, PNAEG-7-010-89, Gosatomnadzor of Russia, Energoatomizdat, 1991). The same practice has developed abroad. Thus, it is believed that initially (before the ND) in the product there were those defects that were revealed during the inspection, and after inspection and repair of the detected defects there were no more. However, it is known (for example, Gurvich AK “Reliability of flaw detection control as the reliability of the complex“ Flaw detector - operator - medium ”, Flaw detection, 1992, No. 3, pp. 5-13), that in almost all cases of ND there is a significant probability skipping defect large sizes exceeding permissible sizes. In practice, it turns out that almost always after ND and repair of detected defects in the product, defects still remain. It is these defects that ultimately determine the reliability and performance of the product.

Known methods for determining the defectiveness of the product, which determine the initial defectiveness of the product, however, there is no evidence that the detected defects are defects in the product. As a rule, defects still remain in the product.

Thus, the known methods do not provide complete identification of defects and do not allow the assessment of defects missed during inspection, which negatively affects the reliability and performance of the product.

Closest to the claimed one is a method for determining the defectiveness of a product (GOST 14782-86), according to which a standard sample is manufactured with a small defect obtained by drilling or milling, by which sensitivity is determined, which determines the reliability of this control method (and control means). It is believed that the higher the sensitivity, the higher the reliability of the NK, but the quantitative characteristics of this relationship in the specified method has not been established, i.e. the method does not allow to evaluate the real defect both before and after repair of the identified defects.

The technical result to which this invention is directed is that it allows you to evaluate the actual defectiveness of the product both before the inspection and after the inspection and repair of the identified defects, and also due to the knowledge of the original (before inspection) and the residual (after checking and repairing the detected defects) defectiveness of the product increases the accuracy of the assessment of the real state of the product, there is the possibility of reliable and safe operation, it is possible to more accurately judge the acceptability of certain methods NC rows, quality products manufacturing technology. The method also allows, if necessary, to take reasonable measures to improve the quality and reliability of the product to an acceptable level.

The problem is solved in that in the method for determining the defectiveness of the product, including the manufacture of a test sample designed to determine the characteristics of non-destructive testing of discontinuities in the material of the product, as well as the control of this test sample by the method of non-destructive testing, according to the results of which they judge the reliability of the control, and control products that are produced by the same method as the control of the test sample, the test sample is made in the form of the product or its most critical part from the same material and according to the same technology as the product, with defects located at random with different characteristic dimensions χ, the reliability of the control is determined as the probability of detecting defects P _water (χ):

where N _obn is the number of defects detected during the control of the test sample,

N _{Hall then} - the number of defects in the manufacture of the sample,

when inspecting the product, the control results are presented in the form of a histogram in the coordinates (χ, N _{obn ed} ), where N _{obn ed} is the number of defects of a given size detected during the inspection of the product,

determine the initial defectiveness N _ref :

determine the residual defectiveness N _ost as the difference N _ref and N _{obn ed} .

As a rule, the linear size of the defect, or a combination of the linear dimensions of the defect, or the area of the defect, or the volume of the defect, is chosen as the characteristic size χ of the defect.

As a rule, the resulting histogram is approximated by an equation of the type

или

или

или

N _ref = A exp (-nχ), or

or

or

or

where a, c are the linear dimensions of the defect,

F is the area of the defect,

n, A are the coefficients selected from the condition of maximum approximation of the analytical curve to the experimental data.

в области дефектов, важных для безопасности, определяют в виде числа дефектов в изделии, размеры которых равны или больше критических размеров χ_кр в режиме эксплуатации изделия:In order to divide the defect into groups of defects important for safety, reliability and manufacturing quality, three groups of defects are introduced into the test sample: defects whose sizes lie in the range from the sizes of defects acceptable during operation to sizes critical for products in operation mode; defects, the sizes of which lie in the range from the dimensions allowed during the manufacture of the product, to the sizes of defects permitted during operation; defects whose sizes are in the range from the sizes minimally available for detecting defects to the sizes of defects acceptable during manufacture, while the first two types of defects mimic defects of an operational nature, and the third type mimics technological defects, residual defects

in the field of defects important to safety, it is determined as the number of defects in the product, the dimensions of which are equal to or greater than the critical dimensions χ _cr in the operation mode of the product:

в области дефектов, важных для надежности, определяют в виде числа дефектов, размеры которых превышают размеры дефектов χ_д.э., предельно допустимых в эксплуатации изделия:residual defectiveness

in the area of defects important for reliability, they are determined as the number of defects whose dimensions exceed the dimensions of the defects χ _doe maximum permissible in the operation of the product:

в области дефектов, определяющих качество изготовления, в виде числа дефектов, размеры которых превышают размеры χ_изг допустимых при изготовлении несплошностей:residual defectiveness

defects in determining the workmanship, as the number of defects that are larger than the dimensions χ _mfd permissible in the manufacture of discontinuities:

where χ _before - the maximum possible characteristic size of the defect.

Figure 1 schematically depicts a defect in the pipeline, figure 2 shows the distribution of defects of critical sizes, allowable for operation dimensions, and allowable discontinuity sizes during manufacturing (the corresponding manufacturing standards are given in table NTD PNAEG-7 010-89), Fig. .3 - characterization of the reliability of the ND in the form of the dependence of the probability of detecting defects P _water on its size (in this case, width a), in Fig. 4 is a histogram of defects detected in the product, in Fig. 5 is the initial defectiveness of the product, in Fig. 6 - residual def ktnost products.

The method is used for a specific product or group of similar products, the quality of manufacture, the reliability and safety of which must be ensured using the well-known NK method, when an operator controls a well-known skill.

Before the manufacture of the test sample by the methods of fracture mechanics, the sizes of discontinuities of a critical size are determined, which are important for determining the safety of operation of the product, taking into account the loads in the operating mode; sizes of defects, the maximum permissible in operation, relevant to determine the reliability of the product; allowable sizes of discontinuities in the manufacture (product defect norms), determined by the applicable regulatory documents and / or technical specifications for manufacturing. It should be noted that defects that determine quality are defects whose sizes are in the range from the minimum dimensions available for detecting defects (search) to the sizes of defects acceptable during manufacture and above; defects determining reliability - these are defects whose sizes are in the range from defective during manufacture to acceptable during operation and above; defects defining safety - from acceptable during operation to critical sizes and above.

Taking into account real operational loads and conditions, defects (discontinuities) are determined for the product (for example, the pipeline, Fig. 1) by the methods of fracture mechanics (taking into account safety factors).

The distribution of defects of critical dimensions (curve 3), allowable sizes in use (curve 2), as well as the allowable sizes of discontinuities in the manufacture (curve 1) are shown in Fig.2.

The test sample is made in the shape of the product and on a scale of about 1: 1 to the product or its most critical part. The most critical part of the product is that part of the product in which the most likely occurrence of defects (welds, places of maximum operational influences, etc.) or the destruction of which is dangerous. The test sample is made of the same material and using the same technology as the product. Three types of artificial defects are laid in test samples:

- defects whose sizes lie in the range from the sizes of defects admissible during operation to sizes critical for the product in the mode of operation of defects,

- defects, the sizes of which lie in the range from the sizes allowed during the manufacture of defects to the sizes of defects allowed during operation,

- defects, the sizes of which lie in the range from the minimum dimensions available for detecting defects to the sizes of defects that are permissible during manufacture (it is also permissible that the upper boundary of the interval exceed the dimensions of defects that are permissible during manufacture).

In this case, the first two types of defects (discontinuities) should imitate defects of an operational nature, and of the third type - technological. Operational defects - defects that can develop from technological defects or arise and develop under the influence of operational loads (fatigue cracks, stress corrosion cracking cracks, etc.), technological defects are defects whose occurrence is associated with the features of manufacturing or installation technology (lack of fusion, non-fusion, pores, etc.). At the same time, it is possible to bookmark a different combination of types of defects (one, any two, three), if necessary, it is also possible to produce a different number of samples, in each of which one type of defects or their different combination will be laid.

All embedded defects must be hidden from PC operators, i.e. be internal (subsurface) or, if the defect is superficial, be located in a place inaccessible to visual detection (or have dimensions that cannot be visually fixed).

It should also be noted that defects are randomly placed in the sample, for example, using random number tables.

The minimum allowable distance between defects is determined on the basis of the condition for the existence of single defects (if single defects are laid) or less for group cracks (the conditions of mutual influence are known, for example, Guidelines MP 108.7-86, M., TSNIITMASH, 1986).

The number of defects of each type should be sufficient for statistical processing of the results, for example, at least 9 pieces. (With less results are less reliable).

Any defect can be conservatively modeled by a crack, and any crack can be described by an ellipse with semi-axes: short a and long c.

There are various options for bookmarking defects in the test sample.

Defects in the form of ellipses are laid in the test sample, and the ratio of the axes of the ellipse is taken on the basis of the condition for the maximum growth rate of the defect in the operational stress field.

Defects in the form of ellipses are laid in the test sample, while the ratio of the axes of the ellipse is arbitrary, and the area of the plane defect or the projection area of the volume defect on the plane of the probable development of the defect is taken as characterizing the size of the defect.

Defects in the form of ellipses are laid in the test sample, while the number of defects and the ratio of the axes of the ellipse are selected using mathematical methods for planning the experiment, based on the condition of minimizing the number of defects to be laid (H. Daniel. Using statistics in an industrial experiment, M .: Mir , 1979).

If the defects to be inserted into the test sample do not have the shape of an ellipse, then they are schematized by ellipses.

After the manufacture of the test sample, it is controlled using the same means and methods of control and by operators of the same qualifications, which will then be used to control the product, the results of the control are compared with real defects embedded in the test sample.

For each characteristic size of the defect, reliability is determined as a function of the probability of detection of defects P _water (χ):

where N _obn is the number of defects detected during the control of the test sample,

_Hall N is the number of defects incorporated in the manufacture of the sample.

Based on the control results, a probability curve for detecting defects for a given part is constructed using this NDT method, depending on the characteristic size of the defects. The probability curve for detecting defects from the dimensions of defects “a” and “c” (any defect in the material can be conservatively described by an ellipse with half axes a and c) can be approximated by the equation that most closely describes the experimental results of control, for example

where α _NK - reliability coefficient of NK, characterizes the increase in the detection of defects depending on its size;

ε is a constant characterizing the ultimate detectability of the control by this method for an arbitrarily large defect size; if the dimensions of the part are small, then this value can be neglected by introducing an appropriate adjustment of the value of α _NC ;

χ is the characteristic size of the defect, for example, its area;

χ ₀ is the minimum characteristic size of the defect;

and ₀ , c ₀ are the minimum defect sizes available for detecting ND.

Next, the product is inspected, and the inspection results are presented in the form of a histogram in the coordinates "characteristic defect size χ - the number of detected defects of a given size N _{obn ed} ."

или

или их аналогами типа

или

The initial defectiveness N _ref is defined as the ratio of N _{obd ed} / P _water (χ), the resulting histogram is approximated by an equation of the type N _ref = A exp (-nχ), or

or

or their analogs like

or

where a, c are the linear dimensions of the defect,

F is the area of the defect,

n, A are the coefficients selected from the condition of maximum approximation of the analytical curve to the experimental data.

Residual defectiveness is obtained as the difference between N _ref and N _ed. In this case, N _{obs. ed} can be taken both directly from the control results and from the analytical expression of N _ex · P _water (χ), in the latter case, the residual defectiveness of N _ost can be represented as the equation

в области дефектов, важных для безопасности, определяют в виде числа дефектов в изделии, размеры которых равны или больше критических размеров χ_кр в режиме эксплуатации изделия:Residual

in the field of defects important to safety, it is determined as the number of defects in the product, the dimensions of which are equal to or greater than the critical dimensions χ _cr in the operation mode of the product:

в области дефектов, важных для надежности, определяют в виде числа дефектов, размеры которых превышают размеры дефектов χ_д.э., предельно допустимых в эксплуатации изделия:residual defectiveness

in the area of defects important for reliability, they are determined as the number of defects whose dimensions exceed the dimensions of the defects χ _doe maximum permissible in the operation of the product:

в области дефектов, определяющих качество изготовления, в виде числа дефектов, размеры которых превышают размеры χ_изг допустимых при изготовлении несплошностей:residual defectiveness

defects in determining the workmanship, as the number of defects that are larger than the dimensions χ _mfd permissible in the manufacture of discontinuities:

where χ _before - the maximum possible characteristic size of the defect.

The method is illustrated by the following example.

1. Product: main circulation pipeline of a power reactor installation.

Product characteristics: steel type 22K with yield strength = 320MPa, clad on the inside of the pipeline with austenitic stainless steel; welds are located both across the axis of the pipeline and along the axis; wall thickness for the base metal of the pipeline - S = 34 mm; the inner diameter of the pipeline is D = 800 mm.

Product operating conditions: operating temperature - 280 ° C; working pressure - 80 kg / cm ² ; the assigned service life is 30 years.

2. Acceptable at the manufacturing stage (quality standards), hidden discontinuities, operational defects and critical defects are shown in FIG. 2, respectively, by curves 1, 2, 3.

3. A test sample is prepared containing flat defects of a technological nature such as fusion and hot welding cracks (Table 1).

4. Determine the reliability of the NC using the method (ultrasonic, eddy current, radiographic and other methods of NC), technical means and operator of the NC of a certain qualification, which will also be used in the control of the product. The results of determining P _water from a are presented in Fig.3.

5. Conduct NK products using the same means and method and operators of the same qualifications as in the control of the test sample (when determining the reliability of NK). The control results are presented in the form of a histogram in figure 4.

6. Using the numerical values of N _{obd ed} from the histogram (figure 4) and P _water from the graph (figure 3) determine the initial defect N _ref . The results of the determination of N _{ref are} presented in the form of a graph in FIG. 5 in the coordinates of N _ref - the characteristic size of the defect (in this case, the width of the defect a, schematically the defect is shown in figure 1).

7. The graph of residual defects N _ost is presented in the same coordinates as for N _ref , in Fig.6. For N _ost produced for every fixed value of a subtraction value of the number N _ref of detected defects.

8. We determined the number of defects remaining in the product after repair and repair of detected defects, and it was obtained that:

the total number of defects, the sizes of which are equal to or exceed the critical dimensions of the defects in operation, amounted to:

the total number of defects, the sizes of which are equal to or exceed the allowable sizes of defects in operation, amounted to:

the total number of defects that are unacceptable during the manufacturing process according to the norms of discontinuities for manufacturing, amounted to:

9. Based on the results, we can draw the following conclusion:

the manufacturing technology of the product and / or the NK technology need to be improved, because in the case of transferring the product to operation, up to 23 defects of unacceptable dimensions will be detected as a result of operational ND, which will lead to additional repair of the product under operating conditions (which is a more expensive measure than factory repair), and in case of missing defects According to the results of operational control, an accident may occur with partial or complete destruction of the product (in this case, the pressure pipeline).

Thus, if you are guided by regulatory documents PNAEG-7-010-89, the product after manufacturing, NC and repair of the identified defects can be allowed to operate. However, the determination of the characteristics of the initial (before the ND) and residual (after the ND and repair of the detected defects) defects indicates a low level of reliability of the product and the need for its improvement.

Claims (4)

1. The method of determining the defectiveness of the product, including the manufacture of a test sample designed to determine the characteristics of non-destructive testing of discontinuities in the material of the product, control of this test sample by the method of non-destructive testing, which are used to judge the reliability of the control, and control of the product, which is performed by the same method as the control of the test sample, characterized in that the test sample is made in the form of the product or its most critical part from the same material and using the same technology as and the product with randomly located defects with different characteristic dimensions χ, the reliability of the control is defined as the probability of detecting defects P _water (χ): P _water (χ) = N _obn (χ) / N _zn (χ), where N _obn - the number of defects detected during the control of the test sample, N _Hall - the number of defects incorporated during the manufacture of the sample, during the control of the product, the control results are presented in the form of a histogram in the coordinates (χ, N _{obd ed} ), where N _{obd ed} is the number of detected during the control of the product defects of a given size, determine the outcome hydrochloric defectiveness N _ucx: N _ucx (χ) = N _{expos ed} (χ) / P _treatment (χ), determine residual defectiveness N _ost as the difference N and N _{ucx upd ed}

residual imperfection N ^Σ _{ost, over} in the region of defects important for reliability, is determined as the number of defects whose dimensions exceed the dimensions of the defects χ _doe maximum permissible in the operation of the product:

residual imperfection N ^Σ _{ost, out} in the region of defects that determine the quality of manufacture, in the form of the number of defects whose dimensions exceed the dimensions χ out _of allowable for manufacturing discontinuities:

where χ _before - the maximum possible characteristic size of the defect. 2. The method according to claim 1, characterized in that the linear size of the defect, or a combination of the linear dimensions of the defect, or the area of the defect, or the volume of the defect, is selected as the characteristic size χ of the defect. 3. The method according to claim 1 or 2, characterized in that the resulting histogram is approximated by an equation of the type N _ref = A exp (-nχ), or N _ref = A _χ χ ^-n _x , or N _ref = A _and a ^-n _a , or N _ref = A _{a, s} (a ² / s) ^-n _a.c , or N _ref = A _F F ^-n _F , where a, c are the linear dimensions of the defect, F is the area of the defect, n, A is coefficients selected from the condition of maximum approximation of the analytical curve to the experimental data. 4. The method according to claim 1, characterized in that the test sample contains three groups of defects: defects whose sizes lie in the range from the sizes of defects acceptable during operation to sizes critical for the product in operation, defects whose sizes lie in the range from the dimensions acceptable in the manufacture of the product to the sizes of defects acceptable during operation, defects whose sizes lie in the range from the sizes minimally available for detecting defects to the sizes of defects acceptable in the manufacture, while the first two types of defects imitate defects of an operational nature, and the third type - technological ones, residual defects N ^Σ _{ost, safety} in the area of defects important for safety, is determined as the number of defects in the product whose dimensions are equal to or greater than the critical dimensions χ _cr in the mode of operation of the product .

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