RU2499255C1 - Method to detect inner exfoliation of pipe walls - Google Patents

Abstract

FIELD: measurement equipment.

SUBSTANCE: pipe surface is prepared for ultrasonic control, scanned with an ultrasonic converter connected to a device, and detection of exfoliated places by readings of the device, at the same time the grid of coordinates is applied on the controlled surface, measurements of pipe wall thickness are made in each cell of the grid of coordinates serially by two converters with different operating frequencies, availability of inner exfoliation is determined on the basis of difference of wall thickness values recorded in each cell of the grid of coordinates by two converters, and variation of the number of cells with values of thickness, making 20…80% of the nominal value of the pipe wall thickness.

EFFECT: increased accuracy of detection of inner exfoliation of pipe walls with availability of access only to outer surface of a pipe.

4 cl, 2 dwg

Description

The invention relates to the diagnosis of pipe walls and can be used to identify internal delaminations of the pipe walls of operating pipelines.

There is a method of detecting internal delamination of the walls of pipes, which consists in cutting the pipe wall and detecting delamination visually on the etched or etched surface of the cut [Konakova MA, Birillo IN, Osennaya TN On the effect of metal bundles on the performance of gas pipelines // Repair, restoration, modernization. - 2007. - No. 1. - S. 45-48].

The main disadvantage of this method is the need to destroy the control object.

A known method of acoustic emission (AE) control of the technical condition of the pipeline, which consists in the fact that AE converters are placed along the length of the pipeline, load the pipeline, register acoustic emission signals and judge by the parameters of acoustic emission signals the degree of damage to the pipeline, characterized in that the pipeline is equipped stationary AE converters, each of which is installed in a sealed protective case and pressed with a calibrated force to the body of the pipeline by means of clamping nastki through providing maximum acoustic contact of the AE converter with the body of the pipeline contact lubricant, and contains a cable with a connector at the end, placed in a protective casing and brought out through the protective channel to the ground, while the AE converter is switched at a predetermined frequency with the mobile hardware of the AE system [ cm. RF patent No. 2207562, IPC ⁷ G01N 29/14, publ. 06/27/2003].

The disadvantage of this method is the significant complexity and duration of the control procedure, and if there are several types of acoustically active defects on the controlled section of the pipeline (cracks, internal delamination), it is impossible to isolate the acoustic signals arising in the pipeline due to the presence of each of the defects.

A known method of thermographic detection of continuity defects in a solid, which consists in the thermal effect on the object of control and registration on the outer surface of the emerging thermal field [Zavidey V.I., Zotov K.V. New methods and devices in non-destructive testing of metal stratifications of pipelines and vessels when working in a hydrogen sulfide environment //].

The disadvantage of this method is the need to use highly sensitive (at least 0.03 ° C) thermal imaging systems that allow you to evaluate the thermal field on the surface being monitored, as well as calibration standards for interpreting the results of the control.

The known method of ultrasonic detection of internal discontinuities, taken as a prototype, which consists in preparing the controlled surface of the pipe for ultrasonic testing, scanning it with an ultrasonic transducer connected to the device (thickness gauge, flaw detector), and identifying the places of delamination according to the testimony [RD 24.200.13- 90 Steel seamless pipes. The technique of input ultrasonic continuity control].

The disadvantage of this method is the inability to recognize the type of defect (internal delamination of the wall, corrosion or erosion thinning of the pipe surface) in the absence of access to the inner surface of the pipe for visual inspection of its condition.

The objective of the invention is to provide a method that allows to level the disadvantages of the prototype.

The technical result manifested in the implementation of the invention is expressed in increasing the accuracy of detecting internal delamination of the pipe walls with access only to the outer surface of the pipe.

The task and technical result in a method for identifying internal delaminations of pipe walls, including preparing the surface of the pipe for ultrasonic testing, scanning it with an ultrasonic transducer connected to the device (thickness gauge, flaw detector), and identifying the places of delamination according to the readings of the device is solved by applying coordinate grid, measure the wall thickness of the pipe in each cell of the coordinate grid in series by two transducers with different working often they determine the presence of internal delamination based on the difference between the wall thickness values recorded in each cell of the coordinate grid by two transducers, and the change in the number of cells with thickness values of 20 ... 80% of the nominal value of the pipe wall thickness, while the transducers should not differ in operating frequencies less than two times, the size of the cells of the coordinate grid should not exceed twice the diameter of the piezoelectric plate of the transducer, and the identification sign of the internal bundle is Xia changing thicknesses not less than 10%, determined on the basis of the values for the two sensors at the control point, and the change is not less than 1.5 times the number of cells with readings of 20 ... 80% of nominal wall thickness.

To understand the essence of the invention, we note that the method is based on the ability of ultrasonic waves to reflect from a defect or to bend around it depending on the ratio of the wavelength and the geometric dimensions of the defect.

The method is implemented as follows. The pipe surface is prepared for ultrasonic testing, a coordinate grid is applied to the controlled surface, the pipe wall thickness is measured in the center of each coordinate grid cell with an ultrasonic device with a sensor with a higher operating frequency, the number of cells N ₁ in which the wall thickness is 20 ... 80% of its nominal value, measure in the cells of the coordinate grid the wall thickness with a thickness gauge with a sensor with a lower working frequency, determine the number of cells N ₂ in which the wall thickness constitute 20 ... 80% of its nominal value, determine the value of the ratio N ₁ / N ₂ and change the readings of the thickness gauge Δδ at each control point, identify the presence of internal delamination by the values of the ratios N ₁ / N ₂ and Δδ. In this case, an identification sign of internal delamination is a change in the thickness Δδ at the control point by at least 10%, and the ratio of the number of cells with readings of 20 ... 80% of the nominal value of the wall thickness is not less than 1.5 times.

Example.

In the process of ultrasonic thickness gauging of the elements of the above-ground piping (outer diameter 720 mm, nominal wall thickness 15.5 mm) of the compressor station, a tube element was found that has a thickness of 6.1 ... 9.4 mm in a section 210 × 150 mm (39 , 4 ... 60.6% of the nominal wall thickness). In the event that the recorded values are due to a decrease in the wall thickness of the pipe element, then it must be replaced due to insufficient strength, and if the registered values are due to the internal delamination of the wall, the pipe element does not need to be replaced, since it has the strength sufficient to ensure further safe operation .

To determine the cause of the anomalous values of the wall thickness of the tube element, two piezoelectric transducers (hereinafter referred to as the probe) with an operating frequency of 5.0 and 2.5 MHz, with a piezoelectric plate diameter of 12 and 8 mm, respectively, were used. For measurements, a coordinate grid with a mesh size of 10 × 10 mm was applied to the outer surface of the controlled section of the tube element.

Figure 1 shows the results of ultrasonic thickness gauge (mm) of a section of a tube element when measured with an ultrasonic thickness gauge UT-93P with a piezoelectric transducer with an operating frequency of 5.0 MHz, figure 2 shows the results of ultrasonic thickness gauge (mm) of the same section with an ultrasonic thickness gauge UT- 93P with a piezoelectric transducer with an operating frequency of 2.5 MHz.

The number of control points on the site: 315.

When measuring at control points with an ultrasonic thickness gauge UT-93P with a probe with a working frequency of 5.0 MHz, the thickness values were: at 115 control points 15.3 ... 15.4 mm, at 200 control points 6.1 ... 9.4 mm ( 39.4 ... 60.6% of the nominal wall thickness), i.e. N ₁ = 200.

When measuring at control points with an ultrasonic thickness gauge UT-93P with a probe with a working frequency of 2.5 MHz, the thickness values were: at 310 control points 15.4 ... 15.5 mm, at 5 control points 8.8 ... 9.6 mm ( 56.8 ... 61.9% of the nominal value of the wall thickness), i.e. N ₂ = 5.

The ratio of the number of grid cells with wall thickness values ranging from 20 to 80% of the nominal wall thickness of the pipe element is N ₁ / N ₂ = 200/5 = 40.

Changes in the readings of the thickness gauge Δδ at each control point when using probes with operating frequencies of 5.0 MHz and 2.5 MHz were determined by the formula:

, $$\Delta \delta =\frac{|{\delta }_{\mathrm{5,0}}-{\delta }_{\mathrm{2,5}}|}{\min ({\delta }_{\mathrm{5,0}};{\delta }_{\mathrm{2,5}})}\mathrm{one\; hundred}\%$$

,

where δ _5.0 ; δ _2.5 - the value of the wall thickness recorded at the point of control of the thickness gauge when using probes with operating frequencies of 5.0 and 2.5 MHz, respectively.

Changes in the readings of the thickness gauge Δδ in the cells of the coordinate grid amounted to 10.5 ... 154.1%.

Thus, Δδ = 10.5 ... 154.1%, N ₁ / N ₂ = 40, i.e. In the pipe wall, internal delamination was revealed.

To verify the reliability of the proposed method, the dismantling of 12 elements of the piping, which after the implementation of the proposed method revealed the presence of internal delaminations of the walls and determined the presence of defects by visual inspection of the inner surfaces of the elements, as well as the cutting surfaces, performed on sections of pipe elements with anomalous values thickness.

The results of the experimental verification at all 12 objects confirm the reliability of the proposed method.

Claims (4)

1. A method for detecting internal delaminations of pipe walls, including preparing the pipe surface for ultrasonic testing, scanning it with an ultrasonic transducer connected to the device, and identifying delamination places according to the readings of the device, characterized in that a coordinate grid is applied to the surface to be monitored, and pipe wall thickness is measured. in each cell of the grid, successively by two transducers with different operating frequencies, determine the presence of internal stratification based on the difference and wall thickness values recorded in each cell of the grid by two transducers, and changes in the number of cells with thickness values of 20 ... 80% of the nominal pipe wall thickness. 2. The method according to claim 1, characterized in that the identification sign of internal delamination is a change in the wall thickness of the pipe by at least 10%, determined based on the values recorded by two sensors at the control point, and a change of not less than 1.5 times the number of cells of the grid with indications of 20 ... 80% of the nominal wall thickness. 3. The method according to claim 1, characterized in that the measurements are carried out by ultrasonic transducers with operating frequencies that differ by at least two times. 4. The method according to claim 1, characterized in that the size of the cells of the coordinate grid should not exceed twice the diameter of the piezoelectric plate of the transducer.

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