RU2263333C2 - Method for detection of disruptions of insulating cover of underground pipeline - Google Patents

Abstract

FIELD: diagnosis and control.

SUBSTANCE: as source of electromagnetic field of cathode protection of pipeline is used. Depth of position of pipeline axis is determined on basis of magnetic transverse, longitudinal and vertical components of electromagnetic field of current of cathode protection of pipeline. longitudinal electric component of electromagnetic current field of cathode protection is measured and transverse component of electromagnetic field of current of cathode protection on the left and right from pipeline axes. Results of measurements are made normal for depth of pipeline, resistance of environment, surrounding pipeline, current force in pipeline, background components of electromagnetic fields. On basis of heightened values of normal electric components of electromagnetic field of cathode protection current position and size of disruptions of isolating cover of pipeline are detected.

EFFECT: higher efficiency.

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Description

The invention relates to the field of diagnostics and condition monitoring of trunk pipelines, and in particular to methods for monitoring the integrity of the insulation coating of pipelines located underground.

A known method for detecting violations of the insulation coating, developed by D. Pearson in the 40s / 1 /.

According to the method of D. Pearson, alternating current is passed through the pipeline, the alternating current source (generator) is connected to the test lead of the cathodic protection system (test point) and the ground electrode. In the case of defects in the insulation coating in the controlled area between the pipeline and the ground electrode, a voltage drop occurs, which is measured with a voltmeter. The described method is used in meters of insulation damage (IPI). As you approach the defective area and, accordingly, increase the voltage drop in the headphones of the device, an audio signal appears, the maximum of which falls on the maximum voltage drop and approximately coincides with the projection of the defect on the earth's surface. After passing through the zone of the defective area, the signal gradually decays. The disadvantages of this method include:

- Difficulty in determining the location of the defective area and assessing the size of the violation of the insulation coating due to the inability to accurately determine the depth of the pipeline.

- High complexity and significant material costs due to the need to connect a current generator to the pipeline and the presence of control and measuring points.

- When processing the results of observations, it is not possible to take into account important parameters: the depth of the pipeline, the current strength in the pipeline, the background components of the electromagnetic field, affecting the value of the values measured by the method.

The closest in technical essence and the achieved result is the relaxation method we took as a prototype for detecting violations of the insulation coating of an underground pipeline, based on the use of an electromagnetic field and known as CIPS - Close Interval Pipe-to-Soil Potential / 2 /. According to the CIPS method, an analysis is made of the changes in the pipe-to-ground potential when switching on and instantly turning off the current, performed at certain intervals along the pipeline using a flexible wire connected to the control and measurement column (CFC) to ensure electrical connection to the pipe. The physical basis of CIPS is the registration of the pipe-to-ground potential using a copper sulfate electrode. The method is based on the registration of on and off potentials and potential gradients with a step of 5 m between the control points. There is a cyclic switching of protective installations (modes: 12 s - “On”, 3 s - “Off”). The axis of the pipeline is determined by the locator when connecting an alternating current source to the pipeline. The voltage drop in the direction perpendicular to the gas pipeline is determined relative to the remote copper-sulfate electrode, which was installed 5 m away from the axis of the pipeline. Since it is necessary to connect to the pipeline to measure the pipe-to-ground potential, this connection is transferred from one control point to another using a cable reel. According to the measured potentials “pipe-to-ground” and the voltage drop in the ground, they receive indications of large damage in the insulation coating and an estimate of their magnitude.

The disadvantages of this method are:

- Due to the impossibility of accurately determining the depth of the pipeline in this way, the preliminary use of an additional device, a locator, is required.

- It is not envisaged to account for the resistance of the rocks of the annulus. It does not take into account that soil, as a rule, is a complex system of formations and sections with different resistances.

- It is not provided that important factors affecting the measurement results are taken into account: the depth of the pipeline, the current strength in the pipeline, the background components of the electromagnetic field, which introduces significant errors in the measurement results.

- High laboriousness and significant material costs due to the need for clear cutting of glades several meters wide over the entire profile, connecting to control and measuring points, using current breakers (syntacts) for short-term shutdown of protective current with their mandatory installation at all closely located cathodic protection stations ( VHC). Syntacts must be installed on all stages of the pipeline (they need at least 12 pieces with a four-thread pipeline system).

- Significant measurement errors are also due to the use of syntacts.

- It is not envisaged to change the electrode spacing depending on the measurement conditions, which leads to the omission of violations of the insulation coating of the pipeline.

- Impossibility of measurements in difficult ground conditions.

The technical result of the invention is to increase, compared with the prototype, the accuracy of determining the location and size of violations of the insulating coating of the underground pipeline, reducing the determination time while reducing costs. The technical result in the known method for detecting violations of the insulating coating of an underground pipeline, which consists in measuring the components of the electromagnetic field, is achieved by determining the depth of the axis of the pipeline by the magnetic transverse, longitudinal and vertical components of the electromagnetic field of the current cathodic protection of the pipeline, sequentially measure the longitudinal electrical component of the electromagnetic field current protection and the transverse component of the electromagnetic field of the current left and right axis of the pipeline, normalize the measurement results to the depth of the pipeline, the resistance of the environment surrounding the pipeline, the current in the pipeline, the background components of the electromagnetic field and the increased values of the normalized electric components of the electromagnetic field of the current cathodic protection determine the location and size of violations of the insulation coating the pipeline.

Salient features of the claimed invention are the following:

- determine the depth of the axis of the pipeline by the magnetic transverse, longitudinal and vertical components of the electromagnetic field of the current cathodic protection of the pipeline;

- along the pipeline, the longitudinal electric component of the electromagnetic field of the current of the cathodic protection is successively measured and the transverse component of the electromagnetic field of the current of the cathodic protection on the left and right axis of the pipeline;

- normalize the measurement results to the depth of the pipeline, the resistance of the environment surrounding the pipeline, the current strength in the pipeline, the background components of the electromagnetic field;

- the increased values of the normalized electrical components of the electromagnetic field of the current cathodic protection determine the location and size of violations of the insulation coating of the pipeline.

The above significant distinguishing features were unknown to us from the patent and scientific and technical literature and are therefore “New”.

At the same time, significant distinguishing features are unknown to the average person skilled in the art, which meets the criterion of "Inventive step".

Due to the fact that the claimed method has passed route testing in the sections of the Ukhta-Torzhok and Gryazovets - St. Petersburg gas pipelines, we believe that the method meets the criterion of "Industrial applicability".

In figure 1. a diagram is presented explaining the proposed method for detecting violations of the insulation coating of the underground pipeline, which shows the axis of the gas pipeline 1, laid in soil 2, into which the receiving electrodes M and N with a spacing of 5 meters are grounded.

Sensor 3 allows you to measure the electrical components of the electromagnetic field of the current cathodic protection of the pipeline in order to determine insulation violations 4.

Figure 2 presents the results of measurements of the electrical transverse X (Ex on the right and Ex on the left) and longitudinal Y (Ey) components of the electromagnetic field of the current cathodic protection of the pipeline.

The method is carried out in the following sequence. An electromagnetic field sensor 3 (having an integrated 50 Hz filter for eliminating industrial interference) at a frequency of 100 Hz using a highly sensitive antenna system (not shown) measures the horizontal and vertical magnetic components of the electromagnetic field of the cathodic protection current.

The above characteristics determine the exact location and depth of the axis of the pipeline.

The measurement of the depth of the pipeline is carried out according to the method described in [3] on p.127-129. The depth of the pipeline h0 is estimated by the formula:

where U1, U2 is the magnetic field strength during measurements using 1 and 2 antennas, respectively, located with a height difference a, Uf is the background component of the field, determined using a vertical antenna, r is the radius of the pipeline.

Two receiving electrodes M and N are grounded to the surface of soil 2 with a spacing of 5 meters, forming a line MN, which is placed along the axis of the pipeline. The electrodes are connected to an electromagnetic field sensor 3 (having a built-in 50 Hz filter to get rid of industrial interference). With this position of the receiving electrodes M and N, the sensor 3 measures the longitudinal electric component Eu of the electromagnetic field of the current cathodic protection of the pipeline. The electrode N is left grounded above the axis of the pipe 1, and the electrode M is grounded on the right side of the axis of the pipe 1 (line NM1), perpendicular to its axis. In this position, the sensor 3 records the value of the transverse electric component Ex on the right of the electromagnetic field of the current cathodic protection of the pipeline. The electrode N is left grounded above the axis of the pipe 1, and the electrode M is grounded similarly on the left side of the axis of the pipe 1 (line NM2), perpendicular to the axis. In this position, the sensor 3 records the value of the transverse electric component Ex on the left of the electromagnetic field of the current cathodic protection of the pipeline. Violations of the insulation coating 4 of the pipeline are marked by increased values of the electrical component of the electromagnetic field. Depending on the conditions and the detail of studying violations of the insulation coating of the pipeline, the observation step is reduced to 1 m, and the electrode spacing is also reduced to 1 meter (the electrode spacing is further taken into account during processing).

The location of the insulation fault 4 is determined by measuring the electrical component when the MN line is located at different angles to the axis of the pipeline 1. At least one of the electrodes is grounded in the region of the axial line of the pipeline 1.

To improve the measurement performance, the values of the electric component of the electromagnetic field are recorded in the memory of the meter using the remote control button (not shown in Fig. 1). Measurements are taken along the entire pipeline in increments of 5 meters. The measurement results are presented in the form of graphs of the electric components of the electromagnetic field of the cathodic protection, maps of the isolines of the electric component of the electromagnetic field and a list of the intervals of the route having violations of the insulation coating 4. The measurement results are normalized to the following factors: the depth of the pipeline, the resistance of the rocks that make up the annular space, strength current in the pipeline, the background components of the electromagnetic field of adjacent pipelines (lead to specific electric Resistance 20 Ohm · m, a current of 1 A, occurrence of a depth of 1.5 m).

The increased values of the normalized electrical components of the electromagnetic field of the cathodic protection current determine the location and size of violations of the pipeline insulation coating.

The background value is determined by measuring the electrical components of the electromagnetic field of the cathodic protection in sections of the pipeline where there are no insulation violations.

The usual magnitude of the anomaly, taken into account, in absolute units is more than 10 mV / m · A (for reduced current 1 A, for reduced pipe depth 1.5 m, for environmental resistance 20 Ω · m).

The magnitude of the violation is estimated by the indicator DF (%) of the damage to the protective coating, which is calculated for individual intervals of the route according to the formula:

where n _df is the number of observation points with values of the electric component of the electromagnetic field that exceeds the "normal line" in the graph by a specified number of times;

N is the total number of observation points in the considered interval.

In addition to graphs of the electric component of the electromagnetic field, the results are presented in the form of tables and graphs DF, as well as a list of pipeline sections recommended for visual inspection in pits.

Example

A section of the Ukhta-Torzhok gas pipeline route (diameter 1020 mm) was laid in wetlands. It is necessary to determine the condition of the insulation coating of the gas pipeline.

The depth of the axis of the pipeline 1, determined by measuring the horizontal X, Y, and vertical Z magnetic components of the electromagnetic field of the cathodic protection current, did not change throughout the study area and amounted to 0.8 m. The current strength in the pipeline is 10 A. The resistance of the swampy environment of the near-tube space is 50 ohm · m. According to the diagram shown in FIG. 1, the electric transverse Ex on the right and Ex on the left and the longitudinal components of the electromagnetic field of the current of the cathodic protection of the pipeline are successively measured. The measurement results at each point are normalized (divided) by the current strength in the pipeline 10 A, the depth of the pipeline 0.8 meters, the medium resistance of the near-tube space 50 Ohm · m, the spacing of the electrodes 5 meters, which increases the accuracy of determining violations of the insulation coating 4 and ensures comparability The results of measurements of the electrical components of the electromagnetic field of the current cathodic protection of the pipeline in various areas.

As a result, on the studied section of the gas pipeline route, according to the increased values of the electric components of the electromagnetic field of the cathodic protection current of the pipeline, an anomalous interval of 110 meters wide is highlighted (shown in gray in Fig. 2). Exceeding the normal field (the value of the field in the absence of insulation violation 4) in the component Eu reaches 180 relative units (relative units), Ex on the right - 75 rel.units, Ex on the left - 6.1 rel. If there are no violations, the Ex values on the right coincide with the Ex values on the left and do not exceed the level of 5 rel.

It is concluded: in the surveyed section of the gas pipeline, a complete absence of insulation coating on the upper generatrix and damage to the insulation coating on the right side of the gas pipeline were detected. Violation of isolation has a length of 110 meters.

A positive result due to the implementation of this method:

- to determine violations of the pipeline insulation, a cathodic protection current field is used and the field generator is not required to be connected to the pipeline;

- determination of the exact location of the axis of the pipeline is provided, which increases the accuracy of determining the location of insulation faults on the generatrix of the pipeline;

- the measurement results are normalized taking into account the following parameters: the depth of the pipeline, the resistance of the rocks that make up the near-pipe space, the current strength in the pipeline, the background components of the electromagnetic field of neighboring pipelines and power lines, which significantly increases the accuracy of studies of the state of the insulation coating of the pipeline;

- 2 operators (not 4) are required for measurements. It does not require the establishment of syntacts (current breakers);

- it is possible to change the spacing of the measuring electrodes depending on the conditions and details of studying violations of the insulation coating of the pipeline. During processing, the measurement results are normalized to the spacing of the electrodes;

- it is possible to detect violations of the insulation coating of the pipeline in difficult grounding conditions (asphalt and concrete pavements, railway crossings, crossings through water barriers, talus debris, frozen ground, snow-ice cover, dry sands) when using non-grounded capacitive devices instead of electrodes.

The claimed method passed the route tests for five years when diagnosing the technical condition of the four phases of the Ukhta-Torzhok gas pipeline and one stage of the Gryazovets - St. Petersburg pipeline.

Sources of information

1. Glazkov V.I. The electric method of finding through damage in the insulation coatings of existing pipelines // "Protection of metals", 1965. - No. 2. - C.21 (Analog).

2. Linds J.M. A new method for detecting pipeline corrosion. part 1. // Oil, gas and petrochemicals abroad. 1993. - No. 7 - S.64-66. (Prototype).

3. Krapivsky E.I., Demchenko N.P. “Geophysical methods for diagnosing the technical condition of underground pipelines” p.127-129.

Claims (1)

A method for detecting violations of the insulation coating of an underground pipeline, which consists in measuring the electromagnetic field components along the pipeline, characterized in that the depth of the axis of the pipeline is determined by the magnetic transverse, longitudinal and vertical components of the electromagnetic field of the cathodic protection current of the pipeline, and the longitudinal electric component of the electromagnetic field of the cathodic current is successively measured protection and the transverse component of the electromagnetic field of the current cathodic protection after and to the right of the axis of the pipeline, the measurement results are normalized to the depth of the pipeline, the resistance of the environment surrounding the pipeline, the current strength in the pipeline, the background components of the electromagnetic field and the increased values of the normalized electric components of the electromagnetic field of the cathodic protection current determine the location and size of violations of the pipeline insulation coating .

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