RU2521714C1 - Method to determine mechanical stresses in steel pipelines - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: method to determine mechanical stresses in steel pipelines involves manufacturing of a pipeline sample from the material identical to the structure material, step loading of the sample, measurement of magnetic parameters of the metal at each loading step with certain positioning of a sensor in respect to the sample, calculation of dependence of the magnetic parameters on the value of stresses in the sample, measurement of magnetic parameters of the pipeline, calculation of the stress value according to the obtained dependence. Self intensity of the pipe metal magnetic field is measured as a magnetic parameter, the measurements are performed at different distances from the measuring sensor to the sample surface, diagrams of dependences of magnetic parameters on the value of stresses in the sample are drawn for each distance, distance from the measuring sensor to the examined pipeline is defined, stresses in the pipeline are defined by the dependence curve corresponding to the distance between the sensor and the pipeline.

EFFECT: expanded functionality of the method.

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Description

The invention relates to the field of assessing the technical condition of pipelines and can be used to determine mechanical stresses in steel pipelines of an underground installation.

A known method for determining the stress state of steel structures, according to which stretch a sample of material cut from a material similar to the material of the structure, in the process of stretching measure the coercive force. The dependence of the coercive force on the applied voltage for a given material is obtained. Then, the coercive force of the metal of the structure is measured and the stress state is determined using the obtained dependence. (V.F. Muzhitsky, B.E. Popov, G.Ya. Bezlyudko. Magnetic control of the stress-strain state and residual life of steel metal structures of lifting structures and pressure vessels. // Defectoscopy. - 2001. - No. 1. - p. 38-46).

A known method of determining stresses, based on the receipt of tensile metal samples with different structural degradation, the dependences of the anisotropy of the coercive force on tensile stresses in the samples and the assessment of stresses in the structure using the obtained dependencies taking into account the actual metal structure (RF patent No. 2281468, publ. 10.08. 2006).

Closest to the claimed method is a method for determining mechanical stresses in steel pipelines, including the manufacture of a sample in the form of a hollow cylinder from a material similar to the structural material, loading the sample by creating excessive internal pressure of a liquid or gas medium or bending it, obtaining a dependence of the coercive force on the value stresses in the sample. Next, measure the coercive force of the existing pipeline and determine its stress state using the obtained dependence (RF patent No. 2439530, publ. 10.01.2012).

The main disadvantage of the known methods is the need to provide local access to the surface of the pipe metal, which is difficult when diagnosing underground pipelines, as well as overhead pipelines having heat-vibration-noise insulation with a thickness of more than 3-5 cm.

An object of the invention is to expand the capabilities of the method.

The problem is solved in that in the method for determining mechanical stresses in steel pipelines, including the manufacture of a pipe sample from a material similar to the construction material, stepwise loading of the sample, measuring the magnetic parameters of the metal at each loading step, with a certain orientation of the sensor relative to the sample, obtaining the dependence of the magnetic parameters from the magnitude of the stresses in the sample, measuring the magnetic parameters of the metal of the pipeline, determining the magnitude of the stress using the obtained dependence, according to the invention, as a magnetic parameter measure the intrinsic magnetic field of the metal of the pipes, perform measurements at various distances from the measuring sensor to the surface of the sample, plot the dependence of the magnetic parameters on the magnitude of the stresses in the sample for each of the distances, determine the distance from the measuring sensor to the controlled pipeline, determine the stress in the pipeline according to the dependence curve corresponding to the measured distance from yes snip to the pipeline.

In figure 1. a stand with a sample is presented for obtaining the dependence of the magnetic field parameters on bending stresses in the sample.

Figure 2 presents graphs of the dependence of the increment of the longitudinal component of the magnetic field strength of the pipeline ΔNu on bending stresses in the sample pipe for the distances between the sensor 2 and the surface of the sample 0.05; 0.1; 0.2; 0.5; 1.0; 1.3; 1.6; 2.0; 2.5 m.

The method is implemented as follows. From a pipe similar in size and material to the pipes from which the controlled pipeline is made, a sample of pipeline 1 is made (Fig. 1).

Sample 1 is placed horizontally. The ends of the sample are rigidly fixed. In the center of the sample, in its upper part, through the spacer 3 of non-magnetic material, a sensor 2 of the meter of the magnetic field component is installed (not shown in Fig.). Orient the sensor so that the measured component Well is parallel to the axis of the sample.

Using a jack 4 mounted in the center of the sample, the bending stresses in the sample are incrementally increased. For each step of loading, the stresses in the sample are determined by a calculation or other method, for example, by means of electrical strain measurements.

At each loading step, the component of the magnetic field strength Well is measured. Several measurement steps are carried out for various sizes of spacers 3, which provide a certain distance from the sensor 2 to the surface of the sample 1. Graphs of the dependence of the increment of the component of the magnetic field strength of the pipeline Well on the bending stresses in the pipe sample for each of the distances between the sensor and the surface of the sample (Fig. 2).

The distance from the surface of the soil to the controlled underground pipeline is determined. On the surface of the soil, the components of the magnetic field strength are measured Well, by installing a sensor above the axis of the pipeline. The points of the pipeline are determined at which there is an increase in the measured value of the component of the magnetic field relative to the average value. Using the dependence obtained on the sample, the longitudinal stresses in the pipeline are determined taking into account the distance from the sensor to the pipeline (the depth of the pipeline).

Example.

It is necessary to determine the longitudinal bending stresses in the section of the underground gas pipeline located in weakly bearing soils. The coordinates of the plot are 0-5,000 km. The pipeline is made of steel pipes 09G2SAF. The diameter of the gas pipes is 1220 mm, the pipe wall thickness is 13 mm.

A stand is made of a similar pipe 11 m long. The pipe (sample) 1 is installed horizontally on concrete blocks 5. To exclude movement, the sample is fixed to the blocks using flexible non-metallic tapes 6 (Fig. 1).

To measure the magnetic field, a magnetometer MAG-01 is used (manufactured by OJSC Giprogazcentr, Nizhny Novgorod).

A jack 4 is placed under the center of the sample.

In the center of the sample, a spacer 3 is installed vertically upward, which ensures a distance between the sensor 2 and sample 1 of 5.0 cm. A spacer 3 is used to install the sensor 2 of the MAG-01 magnetometer (not shown in Fig.), Orienting it so that the tension component measured by the sensor Well field was oriented along the axis of the sample.

Using a jack 4, stepwise stresses are generated in increments of 10.0 MPa, until bending stresses of 250 MPa are created. The level of stress is determined, for example, by measuring the deflection of the sample or determining the effort of movement of the jack and subsequent calculation.

At each test step, the magnetic field component Well is measured. Repeat measurements with 0.1 spacers; 0.2; 0.5; 1.0; 1.3; 1.6; 2.0 and 2.5 m.

The increment of the value of the component of the magnetic field ΔНу at each step of loading the sample is calculated.

The curves of the dependence of the increment of the longitudinal component of the magnetic field strength of the pipeline ΔНу on the bending stresses in the sample pipe for the distances between the sensor 2 and the surface of the sample of 0.05; 0.1; 0.2; 0.5; 1.0; 1.3; 1.6; 2.0 and 2.5 m (figure 2).

On the controlled section of the gas pipeline using the BITA device (manufactured by Giprogazcentr OJSC, Nizhny Novgorod), it is determined that the distance from the soil surface to the upper generatrix of the pipeline is 1.0 m.

Using the MAG-01 device, measurements of the components of the magnetic field around the pipeline are carried out. Well, by installing the sensor of the device over the axis of the pipeline with a step of 1 m

It is established that in the pipeline section there are two points No. 1 and No. 2 with an increase in the magnetic field strength ΔНу of 350 A / m (the coordinate of point No. 1 is 2.123 km) and 300 A / m (the coordinate of point No. 2 is 3.236 km). According to the constructed dependence (Fig. 2), increments of the field strength of 300-350 A / m are typical for bending stresses of the order of 200 MPa at a distance from the sensor to the pipe of 1.0 m. The presence of stresses of this level increases the risk of accidental destruction of the pipeline.

Dig the pipeline at the indicated points. Using non-destructive testing methods assess the condition of the pipe metal.

At point No. 1, local corrosion thinning of the pipe wall is detected with a depth of up to 30% of the nominal wall thickness. It is determined that the bending longitudinal stresses measured by an ultrasonic strain gauge IN - 5101 A (manufactured by Incotes, N. Novgorod) or by a KRM-Ts-K-2M coercimeter are not more than 100 MPa. Thus, the detected change in the magnetic field is caused mainly by local thinning of the wall.

At point 2, no metal wall defects were detected. The longitudinal stresses of the pipe wall, measured in the pit with the IN-5101A instrument and the KRM-Ts-K-2M coercimeter, amounted to about 200 MPa, which is in satisfactory agreement with the results obtained on the basis of the constructed dependence for the distance between the sensor and the pipe 1 m (Fig. 2 )

Claims (1)

A method for determining mechanical stresses in steel pipelines, including producing a pipeline sample from a material similar to the construction material, stepwise loading of the sample, measuring the magnetic parameters of the metal at each loading step with a specific orientation of the sensor relative to the sample, obtaining the dependence of the magnetic parameters on the magnitude of the stresses in the sample, measuring magnetic parameters of the metal of the pipeline, determination of the magnitude of the voltage using the obtained dependence, which differs m, that as a magnetic parameter, the intrinsic magnetic field of the metal of the pipes is measured, measurements are performed at various distances from the measuring sensor to the surface of the sample, graphs of the magnetic parameters are plotted against the magnitude of the stresses in the sample for each of the distances, the distance from the measuring sensor to the controlled pipeline is determined , determine the stress in the pipeline according to the dependence curve corresponding to the measured distance from the sensor to the pipeline.

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