Method of electromagnetic-field flaw detection of ferromagnetic pipes

FIELD: non-distractive testing.

SUBSTANCE: method comprises magnetizing pipe by transverse permanent magnetic field and probing pipe with the use of a set of vortex-current and magnetic sensitive units. The signals from the sensitive units are divided into four groups depending on the type of converter and signal amplitude. The type of defect and its depth can be judged from the signal groups obtained.

EFFECT: enhanced reliability of detection.

1 dwg, 1 tbl

 

The invention relates to the field of nondestructive testing. There is a method of electromagnetic flaw detection based on the scanning of the product of the electromagnetic transducer, counting the total number of pulses from the edges and defects of the product and the release of information about its defects by determining the excess of the total number of pulses over a number of pulse edges from [1]. As electromagnetic transducers use converters or eddy current or magnetic type [2]. In the latter case, to create fields scattering over the defective areas of applied transverse magnetization of the pipe constant magnetic field [3]. The disadvantage of this method [1] is its poor noise immunity and low information.

The purpose of the invention is to improve the information content and reliability of control. This goal is achieved by dividing the detected defects according to their size and the areas of the inside wall of the pipe due to the fact that the pipe is additionally part is subjected to application of a transverse static magnetic field, complemented multielement transducers set with the number m of sensitive elements of the magnetic type (e.g., Hall sensors), placing them sequentially in pairs in the form of adjacent sensing elements eddy current and magnetic type; to anaut the measuring circuit m parallel channels for the measurement signals of the magnetic sensitive elements, as calculated in the interval between edge pulse signals are divided into four groups, the first of which are the pulses appeared simultaneously in pairs of eddy current and magnetic sensitive elements of only one of the number n of the scanning tube of the multi-element transducers, with an amplitude higher than the first level defined by the outer defect specified for this type of defect depth, the second also appeared in these pairs of pulses, but with an amplitude greater than the second level defined by the outer defect twice greater depth; in the third group of pulses, appearing only in magnetic channels with amplitude above the level specified internal defect specified for this type of defect depth; in the fourth signals only magnetic channels with amplitude above the level defined by the internal defect twice greater depth and on the basis of isolated groups of signals, share defects of different depths on the surface and inside, noting the type of defect appropriate labels on the product, or storing in a memory of a programmable device coordinates and characteristics of the defect.

This division is based on the fact that a constant magnetic field magnetizes the pipe throughout the wall thickness, and therefore the magnetic sensors measure signals cacot external defects, located on the outside (closest to the scan Converter side) of the pipe wall, and inner, located in the inner layers, including on the inner side of the wall. Eddy current transducers due to skin effect register signals only external defects.

The drawing shows a block diagram of a device that implements the proposed method.

The device is intended for control of defects in the pipe 3 with the rotational-translational movement. The device consists of two 1 and 2 (n=2) multi-element composite converters with serial pairs of sensitive elements: eddy current (letter) and magnetic (M): pair B1-1, M1-2 to B1-m; M1-m - the first Converter; B2-1, M2-1 to B2-m, M2-m - second Converter; measuring channels BK1-1, MK1-1... BK1-m; MK1-m; BK2-1, MK2-1...BK2-m, MK2-m; programmable unit for logical processing of signals comprising: a programmable microprocessor PM, analog-to-digital Converter ADC, multiplexer for serial connection to the ADC of a given number of measuring channels, finisher BS for generating signals control mechanisms sort of pipes.

The device operates as follows. When scanning the surface of the pipe 3 in each sensitive element of the two opposite multielement is reobrazovateli induced signals from the defective areas, and from the edges of the pipe, as well as interference caused by network problems, shock tube on the rollers of the roller conveyor and other reasons. Each signal from this set has a number of characteristic features. The signals from the defects may not occur simultaneously in the converters 1 and 2 (the probability of such events is quite small), because the defect on the angular coordinate of the tube is very narrow zone. Signals from external defects occur simultaneously as in eddy current. and adjacent magnetic sensitive elements (pairs B1-1, M1-1, B2-1, M2-1 to B1-m M1-m; B2-m, M2-m). The amplitude of the signal correlates with the depth of the defect. The first level is determined by the depth of the minimum defect, which need to be identified. The depth of such a defect is normalized by the standards of tubes. Usually you want to detect defects with depth in % of the wall thickness, more for external defects - 10; for internal average of 15. Important is the allocation of gross defects with depth, approximately two times greater than the minimum depth of the defect. These defects are related to fatal and are the reason that the pipe is not repairable. Defects minimum depth of resolve, Stripping the surface of the pipe in the area of their location, and the pipe is then recognized as suitable for use. The signals from the edges of the tube are formed in all elements of the converters 1 and 2 on sledovatelno with a given duty cycle. After detection of such defects are blocked. Signals from interference occur simultaneously in all the sensory elements of both multi-element transducers 1 and 2 and also blocked. Logical signal processing is performed by a programmable microprocessor connected multiplexer (multi-switch) and analog-to-digital Converter (ADC). The processing algorithm is a sequential polling output signals of the measuring channels VK and MK, registration pulses, the amplitudes of which exceed the first and second levels, and the sorting of these signals in accordance with the characteristics of table 1.

Table 1
The number of option combinationsThe type of channelThe level of the amplitude of the signalThe type of defect
  V1V2
12345
1MK10the outside is first depth of 10% of the wall thickness
 VK10
12345
2MK10the internal depth of 15% of the wall thickness
VK00
3MK11the outer depth of 20% of the wall thickness
VK11
4MK11the internal depth of 30% of the wall thickness
VK00

The described device is tested in a production environment.

Sources of information

1. Copyright certificate № 333460, CL G 01 N 27/86, 1970.

2. Devices for non-destructive testing of materials is impressive and products. Handbook edited Via, M., engineering, 1976, str-139.

3. Nessasarily, Gastronic, Evenj. Contactless system of transverse magnetization of the pipe. Inspection, 1970, 2, p.33.

Way electromagnetic testing of ferromagnetic tubes, which consists in scanning the product set of n shifted relative to each other at an angle of 360/n multi-element eddy current probes with m sensors and the same number of parallel measuring channels; m counting pulses simultaneously introduced in the sensing elements of multi-element transducers shifted by 180°, blocking on this basis of false alarms from the end sections of the product; the count in the interval between the signals from the edges of the number of pulses does not coincide in time of occurrence in the opposite multielement transducers, characterized in that the pipe is additionally part is subjected to application of a transverse static magnetic field, complement multielement transducers set with the number m of sensitive elements of the magnetic type, placing them sequentially in pairs in the form of adjacent sensing elements eddy current and magnetic type, complementary to the measuring circuit m parallel channels for the measurement signals of the magnetic sensor element is in, as calculated in the interval between edge pulse signals are divided into four groups, the first of which are the pulses appeared simultaneously in pairs of eddy current and magnetic sensitive elements of only one of the number n of the scanning tube of the multi-element transducers, with an amplitude higher than the first level defined by the outer defect specified for this type of defect depth, the second also appeared in these pairs of pulses, but with an amplitude greater than the second level defined by the outer defect twice greater depth; in the third group of pulses, appearing only in magnetic channels with amplitude above the level specified internal defect specified for this type of defect depth, in the fourth signals only magnetic channels with amplitude above the level defined by the internal defect twice greater depth and on the basis of isolated groups of signals, share defects of different depths on the exterior and interior, noting the type of defect appropriate labels on the product, or storing in a memory of a programmable device coordinates and characteristics of the defect.



 

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