JP2001272379A - Method and device for non destructive test for tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy for establishing a high quality securing system over the entire circumference, the entire length and the entire surface of a steel tube by sharing flaw detection operation between an ultrasonic flaw detection technique, a magnetic flux leakage flaw detection technique, and an eddy current flaw detection technique for making full use of their features. SOLUTION: A surface flaw is detected by high-frequency magnetization at 8 kHz, then an internal flaw is detected by ultrasonic flaw detection, subsequently an inside surface flaw of the tube is detected by low-frequency magnetic excitation at 0.1-1 kHz, and lastly, magnetic particle inspection in the tube end part is carried out. These processes are carried out in series in one round.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for nondestructively inspecting a pipe.

[0002]

2. Description of the Related Art Cracks, press flaws, holes,
There are various flaws such as inner pit, outer pit, outer fog, outer bite, outer bruise, etc.At pipe making factories, pipes are detected by non-destructive inspection using various detection devices and defective products are excluded. Quality assurance and quality assurance.

For this reason, ultrasonic inspection technology, magnetic flux leakage inspection technology, overcurrent inspection technology and the like are conventionally known as non-destructive inspection technologies, and one or more of these technologies are used for pipe production lines. Non-destructive inspection was performed on the way or offline. Each of these methods has characteristic characteristics.

The ultrasonic flaw detection technique mainly performs detection by oblique flaw detection, and cannot detect a dull shape or a defect having a slow shape due to scattering of a reflected echo. Further, a sharp flaw, a defect parallel to the tube surface, and the like converge and scatter the ultrasonic waves, making it difficult to detect a reflected echo since it cannot be obtained.

Since the leakage magnetic flux technique utilizes high-frequency magnetization, it is not possible to detect defects in austenitic stainless steel having a relative magnetic permeability of 1. In addition, the detection is limited to the defect on the outer surface of the tube due to the magnetic properties and the skin effect of the high-frequency current. Further, in the detection technique using the eddy current, the detection is limited to the defect detection on the outer surface of the tube due to the magnetic properties and the skin effect of the high frequency current.

In the penetrating coil technique, it is difficult to detect a defect extending in the tube axis direction. Further, it is difficult to detect a small defect in the rotating coil system.

[0007]

SUMMARY OF THE INVENTION The present invention improves the accuracy by sharing the flaw detection utilizing the characteristics of each of the conventional ultrasonic flaw detection technology, leakage magnetic flux flaw detection technology, and eddy current flaw detection technology, By using them all in series, it is necessary to establish a high quality assurance system over the entire circumference, length, and entire surface of the pipe.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its technical means is to construct an efficient system combining these techniques. That is, the present invention relates to nondestructive inspection of pipes,
First, skin flaws due to high frequency magnetization of 8 kHz are detected, then internal flaws are detected by ultrasonic flaw detection, and then 0.1 to 1 k
This is a non-destructive inspection method for a pipe, wherein an inner surface flaw of the pipe is inspected by excitation at a low frequency of Hz, and a magnetic particle flaw is detected at the end of the pipe. The present invention makes use of the characteristics of each flaw detection technology to improve the detection accuracy of each, while leaving the low precision parts to be measured by other flaw detection technologies, as a whole, it is an advanced pipe that covers the entire circumference, the entire surface, and the entire length of the pipe. Establish a quality assurance system. 8kHz high frequency magnetization detection frequency
The reason for this is to improve the performance so as to accurately detect flaws in the skin portion on the outer surface of the tube. Conventionally, at a frequency of 1 to 6 kHz, detection of a depth portion of 0.3 to 0.5 mm has been mainly performed, but this can be detected to a depth of 0.1 mm. On the other hand, since a frequency of 16 kHz or more cannot be put to practical use due to heat generation of the magnetizing device as in the prior art, an appropriate frequency was selected by a test and set to 8 kHz. Next, if the frequency of the low-frequency excitation is less than 0.1 kHz, the detection accuracy is poor, and if it exceeds 1 kHz, the detection accuracy of the inner surface of the tube is reduced due to the skin effect of an alternating current.

The apparatus of the present invention which can suitably carry out the above-mentioned method of the present invention includes a high-frequency leakage magnetic flux flaw detector, an ultrasonic flaw detector, a low frequency overcurrent flaw detector, and a magnetic particle flaw detector at the end of a pipe production line. A pipe non-destructive inspection device which is sequentially arranged in tandem.

The reason for limiting to this arrangement is as follows. Water cannot be used for high-frequency leakage magnetic flux from the viewpoint of preventing electrical leakage accidents, but in ultrasonic flaw detection, water is used as a medium to ensure conduction of ultrasonic waves. Therefore, it is appropriate to perform the ultrasonic search after detecting the high-frequency leakage magnetic flux.
In the eddy current detection technology, since the influence of the magnetic field gives a noise to the leakage magnetic flux detection technology and adversely affects the technology, it is necessary to provide a space between the two as much as possible. Therefore, the leakage magnetic flux inspection device, the ultrasonic inspection device, and the eddy current inspection device are arranged in this order, and a tube end defect detection device is provided at the tail end.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an entire system of a pipe nondestructive inspection apparatus 1 according to an embodiment of the present invention. In this non-destructive inspection device 1, a pipe passes through a high-frequency leakage magnetic flux inspection device 2, an ultrasonic inspection device 3, a low frequency overcurrent inspection device 4, and a magnetic particle inspection device 5 in this order.

FIG. 2 is a diagram showing the principle of the high-frequency leakage magnetic flux detection device 2. When a high frequency voltage is applied to the tube 10 with the positive and negative yokes 11 and 12 facing each other to generate a high frequency magnetic flux 13, a leakage magnetic flux 15 is generated at the flaw 14. This leakage magnetic flux 15
Is detected by a probe 16 such as a Hall element. The high frequency magnetic flux leakage flaw detector 2 selects the frequency of the high frequency magnetic flux so as to detect a flaw in the longitudinal direction of the tube existing on the outer periphery of the tube 10 with high accuracy. The high-frequency magnetic flux 13 is intensively generated near the outer skin on the outer surface side of the tube 10 as shown in FIG. Therefore, if there is a flaw 14 near the outer surface of the tube due to the skin effect, the magnetic flux is disturbed, and this is detected with high accuracy. The flaw detection depth δ from the surface of the high frequency magnetic flux leakage flaw detector 2 is represented by the following equation.

[0013]

(Equation 1)

Where f: frequency μ: magnetic permeability of the material σ: electrical conductivity If the frequency f = 8 kHz, δ = 0.2 mm
Becomes

FIG. 8 shows the relationship between the depth of a natural defect and the relative signal intensity by using a defect of defect type A (such as a crack exposed on the surface).
And defect type B flaw (flaw near the surface that is not exposed on the surface)
It shows the result of an investigation for. In the figure, data indicated by a black circle is for defect type A, and data indicated by a white square is for defect type B. The relative signal strength is indicated by an index when the base noise level is 1. Defects with a natural defect depth of 0.2 mm or less are accurately detected.

FIG. 9 is a graph showing the distribution of detection power of the conventional high-frequency leakage magnetic flux flaw detector, and FIG. 10 is a graph showing the distribution of detection power of the high-frequency leakage magnetic flux flaw detector for short flaws according to the embodiment. The X axis indicates the detection level%, the Y axis indicates the defect length mm, and the Z axis indicates the detection probability%. In the conventional device, the defect length is 8mm
Although 100% of the above could be detected, in the present invention, it was possible to detect 100% of a defect having a length of 4 mm or more.

As shown in FIG. 3, the ultrasonic flaw detector 3
The shoe 21 is attached to the outer surface of the tube 1, the ultrasonic transducer 22 is brought into contact with the outer surface of the tube 10 to emit a transmission wave 23, and the reflected wave 24 is detected.
Detects internal flaws within a thickness of 0. The ultrasonic flaw detector 3 accurately detects flaws in the pipe longitudinal direction on the outer circumference and inner circumference of the pipe 10, flaws in the direction crossing the pipe, and lamination. Also,
Used for measuring the wall thickness of the tube 10. In order to ensure transmission of the transmission wave 23 into the tube 10, a medium such as water is interposed between the transducer 22 and the surface of the tube 10 so that the transducer 22 is brought into close contact with the outer surface of the tube 10, To ensure good transmissibility. Since the detection accuracy of the high-frequency magnetization inspection device 2 is impaired by the presence of water or the like, the ultrasonic inspection device 3 is placed downstream of the high-frequency magnetization inspection device 2.

FIG. 6 is an explanatory diagram of characteristics of the ultrasonic flaw detector 3. The ultrasonic flaw detector 3 mainly performs a so-called oblique flaw detection that transmits a transmission wave 23 in a direction inclined with respect to the thickness direction of the tube 10. For example, the transmission wave 23 is incident at an angle of 30 to 50 degrees with respect to the tube radial direction. For this reason, dull or flaws 25 having a slow shape cause scattering of the reflected wave and cannot be detected. Also, it is difficult to detect a sharp shaped flaw. Further, the flaw 26 parallel to the tube surface is difficult to detect because the reflected wave 24 is attenuated due to irregular reflection and convergence.

FIG. 4 is a view for explaining the principle of the low-frequency overcurrent flaw detector 4. The low-frequency overcurrent flaw detector 4 includes an exciting coil 31
An eddy current is generated in the tube 10 by passing a low-frequency current through the differential coil 32. The current and voltage disturbances caused by the presence of defects are detected by the differential coil 32, and defects such as massive flaws and holes are accurately detected. The low-frequency overcurrent flaw detector 4 is limited to detecting defects on the outer and inner surfaces of the tube 10 due to its magnetic properties and skin effect. If the frequency is less than 0.1 kHz, S
The detection accuracy is insufficient due to the decrease in the / N ratio, and if it exceeds 1 kHz, it becomes difficult to detect minute flaws on the inner surface of the tube due to the skin effect. Therefore, the frequency for accurately detecting the flaws on the inner and outer surfaces of the pipe is set to 0.1 to 1 kHz.

In the penetrating coil system, it is difficult to detect a defect extending in the tube axis direction, and in the rotating coil system, it is difficult to detect a small defect.

The magnetic particle flaw detector 5 can accurately detect flaws near the end of the tube. For example, 400m pipe end
When magnetized by about m and the magnetic powder or the magnetic powder liquid is sprayed, the magnetic powder is aggregated and adsorbed on the defective portion to form a pattern, so that the defect can be detected.

In order to complement the advantages and disadvantages of each of the above-described devices, defect detection with high accuracy is achieved as a whole by utilizing the excellent characteristics of each device. FIG. 7 schematically shows the types of flaws present in the material to be detected.
It shows a part of the tube 10, the tube outer surface 41, the tube inner material 42,
This shows a flaw distributed on the inner surface 43 of the pipe. The types of flaws include crack 51, pipe thickness 52, perforated 53, inner pit 54,
An outer pit 55, an outer rash 56, an outer bite or an outer hit 57, and the like. Table 1 shows combinations of these types of flaws and detection devices.

[0023]

[Table 1]

The symbol ◎ shown in Table 1 indicates suitable detection characteristics, and the symbol △ indicates unstable detection characteristics. The equipment is compact, the pinch rolls for holding steel pipes for inspection are minimal, and they are assigned to their respective specialty fields. According to the nondestructive inspection method, it is completely supported.

[0025]

The method and apparatus for non-destructive inspection of a pipe according to the present invention constitute a combined inspection system, and utilize the features of each of the conventional ultrasonic inspection technology, leakage magnetic flux inspection technology, and eddy current inspection technology. In addition to improving the accuracy by sharing the inspections, the use of all of them in series makes it possible to establish an advanced quality assurance system over the entire circumference, the entire length, and the entire surface of the pipe. Defects can be inspected without leakage. In addition, the whole apparatus becomes compact, and conventionally, a plurality of pinch rolls for holding the steel pipe for each inspection were required for each inspection position, but this can be minimized, which contributes to space and cost reduction. .

[Brief description of the drawings]

FIG. 1 is a diagram showing an entire system of a pipe nondestructive inspection apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the principle of a high-frequency leakage magnetic flux flaw detector.

FIG. 3 is a principle diagram of the ultrasonic flaw detector.

FIG. 4 is a diagram illustrating the principle of a low-frequency overcurrent flaw detector.

FIG. 5 is a diagram illustrating the principle of high-frequency flaw detection.

FIG. 6 is an explanatory diagram of characteristics of the ultrasonic flaw detector.

FIG. 7 is a schematic view of a flaw generated on the inner and outer surfaces of the tube.

FIG. 8 is a diagram illustrating the relationship between the depth of a natural defect and the relative signal intensity.

FIG. 9 is a graph showing a distribution of detection power of a conventional high-frequency leakage magnetic flux flaw detector.

FIG. 10 is a graph showing a distribution of detection power of the high-frequency magnetic flux leakage inspection apparatus according to the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Non-destructive inspection device 2 High-frequency leakage magnetic flux inspection device 3 Ultrasonic inspection device 4 Low-frequency overcurrent inspection device 5 Magnetic particle inspection device 10 Tube 11, 12 Positive and negative yoke 13 High-frequency magnetic flux 14 Defect 15 Leakage magnetic flux 16 Probe 21 Shoe 22 Transducer 23 Transmitted wave 24 Reflected wave 25 Dull or slow flaw 26 Flaw parallel to tube surface 31 Excitation coil 32 Differential coil 41 Tube outer surface 42 Tube inner material 43 Tube inner surface 51 Crack 52 Tube thickness 53 Perforated 54 Inner pit 55 Outer pit 56 Outer Irritation 57 External biting or external bruising

Claims (2)

[Claims] 1. In non-destructive inspection of a pipe, first, 8 kHz
Skin defects due to high-frequency magnetization, then detect internal flaws by ultrasonic flaw detection, then inspect the inner surface flaws of the tube by low frequency excitation of 0.1-1 kHz, and finally inspect the end of the tube. Non-destructive inspection method for pipes, characterized by conducting magnetic particle flaw detection. 2. A non-destructive inspection of a pipe, characterized in that a high frequency leakage magnetic flux inspection device, an ultrasonic inspection device, a low frequency overcurrent inspection device, and a magnetic particle inspection device are sequentially arranged in a tandem at the end of a pipe production line. apparatus.