RU2250458C1 - Magnetic defectoscope for testing pipes from inside - Google Patents

Abstract

FIELD: nondestructive testing.

SUBSTANCE: defectoscope comprises magnetic system and Hall-effect transducer. The magnetic system and Hall-effect transducer are mounted in a pressure-tight housing. The transducers are aligned and spaced by (0.3-0.5)T, where T is the thickness of the wall of the pipe to be tested. The top side of each transducer is a tangent to the plane of the faces of the poles of the magnetic system. The planes of the transducers are parallel to the magnetic force lines in the space between the poles.

EFFECT: enhanced reliability.

2 dwg

Description

The invention relates to non-destructive testing of pipes of the main pipeline transport and can be used to detect defects in other objects and products.

There are a large number of magnetic flaw detectors containing magnetic systems and field sensors that are mounted on special movable flippers that slide along the surface of the pipe when the flaw detector moves in the pipe.

For example, the Pipeline Inspection Systems flaw detector for in-line inspection is known (see additional materials), in which the sensors are located in fins that slide along the pipe surface. This design, although it has several advantages, but also has significant drawbacks: when the flaw detector moves in the pipe, the fins move relative to the magnetic system, which increases the level of interference signals and increases the likelihood of damage to the sensors during the passage of welds and other possible obstacles. In addition, the optimum distance between the sensors, excluding the possible omission of defects, has not been determined.

In a magnetic flaw detector (patent 5293117), the sensors are also mounted in a movable element (shoe), which can move relative to the external magnetic system. This device also has all of the above disadvantages.

Closest to the claimed design is a magnetic flaw detector according to patent No. 2204130, containing a magnetic system and sensors located along the line of magnetic neutral. However, the position of the magnetic neutral line on the magnetic neutral plane has not been determined. The irrational position of the sensors in the plane of the magnetic neutral leads either to a significant increase in the interference signal, or to a decrease in the useful signal from the defect.

In all known devices, Hall sensors are installed so that their working faces are perpendicular to the magnetic lines of force in the interpolar space, since it is believed by the general physical essence that the vector of the tangential component of the defect field is directed along the magnetic field lines in the interpolar space. With this installation, Hall sensors work only with a fairly limited field strength in the interpolar space. With increasing field strengths over a certain limit, Hall sensors become saturated. This is one of the reasons for installing sensors in flippers located outside the pole space.

The problem to which the invention is directed is to overcome these drawbacks and increase the reliability of detecting defects in the pipes of the main gas pipeline and the reliability of the magnetic search system in the flaw detector.

The essence of the invention lies in the fact that in a magnetic flaw detector for in-line inspection containing a magnetic system and Hall sensors, the magnetic system and Hall sensors are located in a sealed enclosure, and the sensors are located in one line at a distance of (0.3-0.5) T each from the other, where T is the wall thickness of the pipe being tested, so that the upper face of each sensor touches the plane in which the end surfaces of the poles of the magnetic system lie, and the planes of the sensors are perpendicular to this plane and parallel to the magnetic force Niyama pole space.

The differences of the proposed magnetic flaw detector are as follows:

1. The sensors and the magnetic system are housed in a sealed stainless steel non-magnetic steel housing;

2. The sensors are mounted parallel to the magnetic lines of force in the interpolar space of the magnetic system and perpendicular to the plane of symmetry Q of the magnetic system and plane P, in which the end surfaces of the poles of the magnetic system are located.

3. The sensors are located in one line on the boundary of the interpolar space so that they touch the plane R.

4. The distance between adjacent sensors depends on the depth of the detected defects and on the pipe wall thickness and is (0.3-0.5) T, where T is the pipe wall thickness. With this arrangement of sensors, the presence of a guaranteed gap between the pipe surface and the surface of the block with the magnetic system and the sensors ensures that there is no wear of the elements and reliable sealing of the entire block.

When the flaw detector moves in the pipe, neither the sensors nor the magnetic system touch the pipe surface.

Sealing of Hall sensors and the magnetic system eliminates the influence of destructive environmental factors, ensures their stable and long-term operation.

It was found that when the magnetic system is positioned at an angle of 45 ° (Decision to grant a patent for an invention according to application No. 2002125957) to the direction of movement, a tangential component of the field arises from the defect, the vector of which is directed in the direction of magnetic neutral, which makes it possible to install Hall sensors in parallel with magnetic lines in the pole space. At the same time, Hall sensors do not respond to the pole field, regardless of its intensity, but only signals caused by defects are recorded. This allows you to increase the field strength between the poles of the system, for example, by reducing the distance between the poles, increasing the signal from the defect, which provides a high signal-to-noise ratio and increase the reliability of detection of defects. In addition, the location of the sensors parallel to the magnetic field lines allows you to set the initial signal close to zero. Even a small angle between the plane of the sensor and the direction of the magnetic field lines causes a significant interference signal from the sensor. Moreover, in many cases, the sensors become saturated and lose their ability to perceive a signal from defects.

When a flaw detector moves in a pipe, a defect field and a field from the poles of the magnetic system act on the sensors. The deeper the sensors are located in the interpolar space, the greater the signal from the pole field and the smaller the signal from the defect. When the sensors are located outside the interpolar space, the sensors are affected by the scattered magnetic fields of the poles, which have significant heterogeneity and cause an increase in interference signals. It has been experimentally confirmed that the position of the sensors is appropriate in which their upper face touches the plane in which the end surfaces of the poles of the magnetic system lie, and the planes of the sensors are perpendicular to this plane and parallel to the magnetic field lines of the interpolar space.

As the distance between adjacent sensors increases, the probability of missing a defect increases, so the distance between the sensors is chosen so that a defect located between two adjacent sensors causes a sufficient signal from both sensors. The values of the field parameters above the defect, ceteris paribus, depend on the depth of the defect and on the thickness of the pipe. Given the minimum defect depth that must be detected according to the technical specifications, the optimal distance between the sensors should be equal to 0.3 ... 0.5 of the thickness of the pipe.

The invention is illustrated by drawings.

Figure 1 shows the design of the proposed flaw detector, where indicated:

N1, S1 and N2, S2 are the poles of the inner and outer loops of the magnetic system; 1 - magnetic circuit; 2 - sensors (Hall sensors); 3 - a plate on which sensors are mounted; 4 - end surfaces of the poles; 5 - non-magnetic non-conductive insert; Q is the plane of symmetry of the magnetic system; P is the plane in which the end surfaces of the poles are located.

Figure 2 shows the design of the proposed magnetic flaw detector in projections: a) front view; b) top view.

N1, S1 and N2, S2 are the poles of the inner and outer loops of the magnetic system; 1 - magnetic circuit; 2 - sensors (Hall sensors); 3 - a plate on which sensors are mounted; 4 - end surfaces of the poles; 5 - non-magnetic non-conductive insert; Q is the plane of symmetry of the magnetic system; P is the plane in which the end surfaces of the poles are located; 6 - sealed housing (in cross section); 7 - magnetic field lines; 8 - section of the tested pipe.

An example of the proposed device (magnetic flaw detector for in-line inspection).

The poles N1, S1, N2, S2 are packages of permanent magnets made of neodymium-iron-boron material. The size of one magnet in the pole N1 (S1) is 40 × 40 × 10 mm. The size of the entire pole (package of magnets) is 40 × 40 × 80 mm. The poles N2 and S2 are composed of permanent magnets 40 × 20 × 10 mm in size. The size of the entire pole N2 (S2) is 40 × 20 × 80 mm. The magnetic circuit 1 is made of Armco steel measuring 146 × 80 × 30 mm. Insert 5 and plate 3 are made of PCB. Hall sensors of the SS-495A type were used as field sensors. The distance between adjacent sensors is set 4 ... 5 mm for monitoring pipes with a diameter of 1220 mm. The sensors are installed so that the upper faces touch the plane P and their planes are perpendicular to the planes P and Q. The sensors and the magnetic system are placed in a sealed stainless steel casing.

A block with a magnetic system and sensors is attached to the magnetic flaw detector carrier with six screws. The operation of the device is as follows. When moving in the pipe of a magnetic flaw detector, sensors 2 read signals from the magnetic fields of the defects, which are transmitted to the on-board storage device. After the flaw detector passes through the inspected section of the pipeline, the collected information is processed using special software.

The work of the manufactured sample of the proposed flaw detector was tested on stands with pipes with a diameter of 1220 and 1420 mm. Checking the manufactured device showed that with its use, longitudinal and transverse defects are confidently detected.

The use of the developed flaw detector will ensure its long-term stable work in identifying dangerous longitudinal and transverse defects in the pipes of a gas pipeline.

Claims (1)

A magnetic flaw detector for in-pipe inspection, comprising a magnetic system and Hall sensors, characterized in that the magnetic system and Hall sensors are located in a sealed housing, and the sensors are located in a single line at a distance of (0.3-0.5) T from each other, where T is the wall thickness of the pipe to be tested, so that the upper face of each sensor touches the plane in which the end surfaces of the poles of the magnetic system lie, and the planes of the sensors are perpendicular to this plane and parallel to the magnetic field lines of the interpolar anstva.

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