# The method of determining the probability of defect detection, the initial and residual defects using the results of non-destructive testing

The invention relates to the manufacture, installation, operation, products of modern engineering and instrumentation, including energy, petrochemicals, transportation. The method includes monitoring products using non-destructive testing. For a specific product or group of similar items define critical size defects in the operation mode, valid in operation the size of defects and acceptable manufacturer defects dimensions. The testing results are in the form of a histogram. The histogram approximate equation with constant, which is determined from the condition of maximum approach of the equation to the monitoring results, presented in the form of a histogram. Determine the source of the defect and the probability of defect detection. The residual defect is defined as the difference between the original and the detected defects. In this case the residual defect is determined in three ranges: in the field of defects that are important for safety, reliability and quality workmanship. The method improves the accuracy assessment of the product. 4 C.p. f-crystals, 4 Il.

The scope of the invention is the manufacture, installation and operation of the ed the water), energy (thermal, nuclear, and others), petrochemicals including Nate, gas and product pipelines, vessels and storage, General engineering, etc.,

In accordance with the existing practice in modern technology NC is responsible products after manufacture, before commissioning and during operation. It is assumed that the NC identifies all defects that are available for detection by this method of control. All discontinuities, heterogeneity, and similar anomalies metal, if they exceed the allowed dimensions, are classified as defects and will be repaired by the repair. Believe that after NC and repair identified defects other defects in the product (see, for example, “Equipment and pipelines of nuclear power installations. Welded joints and welding. Control rules”, PNEG-7-010-89, Gosatomnadzor, Energoatomizdat, 1991). The same practice has developed and abroad. Thus, it is believed that the original (to NC) in the product were the defects that were detected in the control process, and after inspection and repair identified defects in the product defects, not a product can be safely operated. However, the assessment as a source of defects in the product, and the mod who take into account the actual detectability of defects, inherent to the used control methods and operators NC with a certain level of classification. It is known (for example, Gurvich N.To. “The reliability of flaw detection control as the reliability of the system “Flaw - operator - environment, Inspection, 1992, No. 3, S. 5-13) that in almost all cases, NC there is a significant probability of missing a defect larger than the permissible size. In practice, it is almost always after NC and repair identified defects in the product is still defective. These defects ultimately determine the reliability and performance of the product.

There is a method of determining the defectiveness of the product, which determines the initial defectiveness of the product, and measured when the control parameters are selected from the best possible testing reliability by reducing the probability of making wrong decisions (USSR author's certificate No. 1406888, 1995).

However, this method does not provide complete removal of residual defects and does not allow its evaluation, which negatively affects the reliability and performance of the product.

Closest to the claimed method is determining definium or milling, which adjusts the sensitivity of determining the validity of this method of control (and control). It is believed that the higher the sensitivity, the higher the reliability of the TC, but the quantitative characteristics of this relationship in the specified method is not set, i.e. the method does not permit the assessment of real defects both before and after repair of detected defects. The disadvantage is that the standard samples are not tied to real designs, dimensions and types of defects that affect the quality, reliability and safe operation of the product, the method makes no assumptions about the actual validity of the tax code.

The technical result, which directed this invention lies in the fact that it is possible to evaluate the reliability of NDT carried out on a single or group of similar products, taking into account all the real features of the product design, technology, manufacturing, testing, qualification and integrity of operators NC, spending control, and other factors affecting the results of the control.

The method allows to evaluate the real defects of the product before kaskadnoi (to control) and residual (after inspection and repair of detected defects) defects of products increase the accuracy of evaluation of the actual state of the product, reliability and safety of its operation, the acceptability of certain methods of NDT, quality technology products. The method also allows, if necessary, to take reasonable steps to improve the quality and reliability of the product to an acceptable level, and to formulate (if required) reasonable requirements for perfection of means and methods of NDT, training and responsibilities of the operators NK.

The problem is solved in that in the method of determining the defectiveness of the product, including control of products using non-destructive testing, for a specific product or group m the same products determine the critical dimensions of the_{kr}defects in the operation mode, valid in operation dimensions []_{D. E.}defects and acceptable in the manufacture of dimensions []_{technology}defects, the inspection results are in the form of a histogram in the coordinates (N_{OBN},), where N_{OBN}- the number of detected during the inspection of defectsthe characteristic defect size, approximate the histogram of the equation

N_{the>exp[-(-0)]-}, (1)}

N_{OBN}()=Aexp(-n){1-(1-)exp[-1(-_{0})]-},

where A, n,,- constant, which is determined from the condition of the best approximation for N_{OBN}(to the monitoring results, presented in the form of a histogram;

_{0}- minimum available for the detection of the defect size

determine the original defect N_{ucx}according to the formula:

N_{Ref}=And^{-n}or N_{Ref}=Ehr (-n), (2)

and the probability of defect detection P_{water}according to the formula:

P_{water}=1-(1-)exp[-(-_{0})]-, (3)

determine residual defects N_{ocm}as the difference N_{ucx}.gif" border="0">in the field of defects, important to safety, defined as the number of defects in the product, the dimensions of which are equal to or greater than the critical size_{kr}in the operation of the product

residual defectsin the area of defects is important for reliability, defined as the number of defects that are larger than the sizes of the defects []_{D. E.}maximum allowable in the use of the product

residual defectsin the field of defects in determining the quality of production, as the number of defects that are larger than the dimensions []_{technology}valid in the manufacture of discontinuities

where_{before}- the maximum possible characteristic defect size

m is the number of the same products.

Generally, as the characteristic dimensiondefect is selected linear dimension of the defect, or a combination of the linear dimensions of the defect, or pasoleteenage all of the inspection results summarize and present in a single histogram.

In particular, the minimum available for the detection of defect size_{0}determine if the flaw detector setup used in the control of the product, or as the minimum size of defect that was detected during the inspection.

In particular, to simplify the calculations, constantis equal to 0.

In Fig.1 shows a schematization of the defect in the pipe; Fig.2 shows the defects of critical size is valid in operation sizes and allowable flaw dimensions during manufacture; Fig.3-histogram of the identified product defects; Fig.4 - the functions of the original defects N_{ucx}(), residual defects in N_{ocm}(and the defect detection probability P_{water}() defined according to the results of NDT products. It is also shown the function of N_{OBN}()=N_{Ref}()P_{water}().

The method is applied to a specific product or group of similar products, quality workmanship, reliability and security which you must provide with the application of osenia determine the critical defect size in the mode of operation for this product_{kr}maximum allowable operation defects []_{D. E.}valid in the manufacture of the size of defects []_{technology}(the norm of the defect), as defined by applicable regulations and/or specifications for the manufacture (the characteristic size of the defect, for example, is selected linear dimension of the defect, or a combination of the linear dimensions of the defect, or the defect area, or volume of the defect). It should be noted that the defects that define the quality is defects whose sizes are in the range from the minimum available for defect detection (search) to the size of defects that are valid in the manufacture and above; a defect determining reliability is the defects whose sizes are in the range from acceptance at the manufacturer to an acceptable during the operation above, the defects that determine the security is valid from when the operation of the critical dimensions and higher.

The distribution of defects of critical size (curve 3), valid in operation dimensions (curve 2), and the allowable size of the discontinuities in the manufacture of curve (1) shown in Fig.2.

Spend nerazrushai TC) and technical means of control operators specific skills.

The testing results are in the form of a histogram in the coordinates of the characteristic defect sizethe number of detected defects of a given size N_{OBN. ed}". The horizontal axismust include a critical size defect, even if the control of all identified defects have not reached a critical size.

In the case of control a few of the same products all inspection results are summed and represented as a single histogram. The greater the number of products was controlled, the more we get the final result.

Structure analytical expressions that can describe the NDT results presented in the histogram, the following

N_{OBN}()=N_{Ref}()P_{water}() (7)

where N_{OBN}- the number of detected during the inspection of defects per unit of characteristic size. If the characteristic size of the selected semi-minor axis of the ellipse, which schematize the defect, then the dimension of N_{OBN}mm^{-1};

n_{Ref}function source (to NC) defects with the same size of the N_{Ref}and R_{water}determined based on the condition of maximum simplicity of expression, the minimum number of constants and compliance physically due to dependency N_{ucx}and R_{water}. In the first approximation can be used the following equations:

N_{Ref}=A^{-n}, (2)

P_{water}=1-(1-)exp[-(-_{0})]-, (3)

N_{OBN}()=A^{-n}{1-(1-)exp[-(-_{0})]-} (1)

where A, n,,,_{0}- constant.

Determine the numerical value of the constant, where A, n,,from the condition of maximum approximation equations N_{OBN}() results of NC, presented in the form of a histogram.

When thisin the first approximation can be taken equal to 0. The result is a three unknowns, which greatly facilitates the task of their definition.

To determine the constants a, n,you can either solving the system of three equations for A, n andwho receive, if we take three points on the histogram, or define them using the method of least squares.

Residual defects N_{ocm}defined as the difference of N_{ucx}and N_{on}

N_{OST}()=N_{Ref}()-N_{OBN}(). (8)

While the number of remaining defects in the product is determined in three ranges: residual defectsin the field of defects, important to safety, defined as the number of defects in the product, the dimensions of which are equal to or greater than the critical size_{kr}in the operation of the product

residual defects]_{D. E.}maximum permissible product use:

residual defectsin the field of defects in determining the quality of production, as the number of defects that are larger than the dimensions []_{technology}valid in the manufacture of discontinuities

where_{before}- maximum characteristic size of the defect in this design with given geometry (e.g., in the direction of thickness of the vessel wall pressure limiting defect size is equal to the wall thickness),

m is the number of the same products.

According to the obtained results make assessment and make decisions

- largest- about the possibility of full or partial destruction of the product in use,

- largest- about the reliability and scope of the repair of the product during operation,

- largest- quality control

- functions of P_{water}() - o reliability of NDT products and the skill level of operators is) about the workmanship, if NK was performed at the factory, or on the extent of damage to the product, if the cause of defects were operational impact).

The invention is illustrated by the following example.

It is necessary to ensure the quality of the two pipes of internal diameter D=800 mm wall thickness S=34 mm from pearlitic steel. Critical size defects in girth welds is shown in Fig.2 (curve 1). Valid in operation defects determined using the equations of fracture mechanics and factors of safety (curve 2 in Fig.2). Norms of defects in the operation shown in Fig.2 curve 3.

In the NC standard method and means prior to the operation (after installation) was detected 47 of discontinuities.

All identified discontinuities (defects) are presented as histograms in Fig.3.

At the same time as the characteristic dimension of the defect selected width of the defect in the direction of wall thickness, but rather the semiminor axis of the ellipse, which was shemaleshemale all identified defects.

With a ratio of/0,5 critical size defect corresponds to

Although the maximum size of the defect detected was_{max}=13 mm, the x-axis contains the critical size=15 mm

The equation describing the number of detected defects N_{OBN}depending on the size and

N_{OBN}=AA^{-n}[1-exp[-(a-a_{0})]. (9)

Control minimum detected defect had_{0}=0.6 mm

To determine the constant A, nsolve system of three equations with respect to these constant:

the 1st equation to get the point with coordinates (=1 mm, N_{OBN}=20) Fig.3

20=A·^{1-n}[1-exp[-(1-0,6)]]; (10)

2nd equation to get the point with coordinates (=5 mm, N_{ESD}=4) Fig.3

4=As·5^{-n}[1-exp[-(5-0,6)]]; (11)

the 3rd equation to get the point with coordinates (=13 mm, N_{OBN}=0,66) on Fig.3

0,66=A·13^{-n}[1-exp[-(13-0,6)]]. (12)

For the 3rd equation of N_{OBN}=0,66 obtained as the averaged number of detected defeatable system of equations has the form

20=A·[1-exp(-0,4)]

4=A·5^{-n}[1-exp(-4,4)] (13)

0,66=A·13^{-n}[1-exp(by 12,4)]

Solving the system of equations for A, ngave the following results

A=1000 mm, n=2,56,=0,05 mm^{-1}.

Substituting the constants a, n,in the corresponding equations, obtain the equation of the original defects

N_{Ref}=1000A^{-2,56}; (14)

the equation of the probability of defect detection:

P_{water}=1-exp[-0,05(a-0,6)]; (15)

equation residual defects

N_{OST}()=N_{Ref}()-N_{OBN}(). (8)

These equations are represented graphically in Fig.4.

Claims

1. The method of determining the defectiveness of the product, including control of products NDT method, characterized in that for a specific product or group m the same products determine the critical dimensions of the_{kr}defects in the operation mode, valid in operation dimensions [OBN, (), where N_{OBN}- the number of detected during the inspection of defectsthe characteristic defect size, approximate the histogram of the equation

N_{OBN}()=A^{-n}{1-(1-)exp[-(-_{0})]-}, or

N_{OBN}()=Aexp(-n){1-(1-)exp[-1(-_{0})]-},

where A, n,,- constant, which is determined from the condition of the best approximation for N_{OBN}(to the monitoring results, presented in the form of a histogram,

_{0}- minimum available for the detection of the defect size

determine the original defect N_{Ref}according to the formula:

N_{Ref}=AndP_{water}=1-(1-)exp[-(-_{0})]-,

determine residual defects N_{OST}as the difference N_{Ref}and N_{OBN}while N_{OST}define three ranges: residual defectsin the field of defects, important to safety, defined as the number of defects in the product, the dimensions of which are equal to or greater than the critical size_{kr}mode of operation:

residual defectsin the area of defects is important for reliability, defined as the number of defects that are larger than the sizes of the defects []_{D. E.}maximum permissible product use:

residual defectsin the field of defects in determining the quality of production, as the number of defects that are larger than the dimensions []_{technology}let the>_{before}- the maximum possible characteristic defect size

m is the number of the same products.

2. The method according to p. 1, characterized in that as the characteristic dimensiondefect is selected linear dimension of the defect, or a combination of the linear dimensions of the defect, or the defect area, or volume of the defect.

3. The method according to p. 1 or 2, characterized in that the control m the same products all inspection results are summed and represented as a single histogram.

4. The method according to any of paragraphs.1-3, characterized in that the minimum available for the detection of defect size_{0}determine if the flaw detector setup used in the control of the product, or as the minimum size of defect that was detected during the inspection.

5. The method according to any of paragraphs.1-4, characterized in that the constantis equal to 0.

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