JPS62232558A - Method for inspecting welded part by eddy current flaw detection - Google Patents

Abstract

PURPOSE:To detect a flaw as the change in impedance, by a method wherein an AC bridge circuit is formed of two element, i.e. for inspection and comparing impedance, while one of which is variable and the axis of an inspection coil is made vertical to a welded surface to take the equilibrium of the circuit to perform scanning in a welding line direction. CONSTITUTION:A sine wave AC having constant frequency is applied to a bridge circuit, which is constituted of an inspection coil 4, a comparing coil 5, a variable impedance element 8 and an impedance element 7, from an oscillator and non-equilibrium voltage is applied to a meter and a synchronous detector to take the equilibrium of the circuit by the element 8. Next, a variable phase shifter 10 is adjusted so that the signal generated by the backrash of a probe 9 an a head 1 appears only in CH2, CH4 and a probe 1 is scanned along the direction of the bead. Whereupon, if there is a crack, said crack appears in the indications of CH1, CH3 as fluctuation. If this fluctuation is recorded, the presence of the flaw or crack of a welded part can be determined.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a so-called non-destructive inspection method for welds, which inspects defects in welds without destroying the object to be inspected. (Prior Art) Conventionally known methods for inspecting defects in welded parts include a single-ray transmission test method, an ultrasonic flaw detection test method, a magnetic particle probe test method, and a penetrant test method. The radiographic testing method is a method in which the image of the radiation that has passed through the object to be inspected is cast onto a film, and a pattern corresponding to the defective area is created.However, a large-scale shielding device is required to prevent radiation damage. So, 4
It is not suitable for on-site inspection of M-stomosis, etc., and when inspecting self-welded parts, there is a large difference in the length of IIl ray transmission of the inspected part, resulting in a large difference in brightness and darkness of the photographed image. However, there was a problem in that it was difficult to detect defective parts. Ultrasonic flaw detection testing is a method of transmitting ultrasonic waves into the test specimen and detecting the ultrasonic waves reflected from the defective part to identify the defective part, but in the case of fillet welding, there may be unwelded parts inside that are not defective. There is a problem that this may be mistaken as a defect, and that the inspection speed is about 30 million melons per day, which means that the inspection takes time. The magnetic particle testing method is a method of detecting defects by magnetizing the ferromagnetic part to be inspected and using the adhesion of magnetic particles due to the magnetic poles generated in the defective part, but because the magnetization device is large, it cannot be used in narrow spaces. There are disadvantages in that the work cannot be carried out and the inspection speed is slow, ranging from about 50 M 7'J to 80 M per day. The penetrant 1n test method uses a highly permeable liquid containing a fluorescent substance or visible dye to visually hide open scratches on the surface of the specimen, and then detects the remaining penetrant on the surface. In this method, the liquid is wiped off, the penetrating liquid remaining in the defect is extracted using a developer, and the defect is observed as an enlarged image of the indicated pattern. When inspecting welds using this method, the surface of the weld bead is uneven, and it takes time to wipe off the penetrating liquid, so it is only possible to inspect a few tens of meters per day. There is a problem in that it cannot be detected, and objects with painted surfaces cannot be inspected. (Problems to be Solved by the Invention) When attempting to inspect a welded part by a method other than the eddy current flaw detection method, there are various problems such as those mentioned above. On the other hand, when attempting to inspect a weld using the eddy current deep flaw method, the magnetic permeability differs between the base metal and the bead, so a large change appears in the impedance when the inspection coil crosses the boundary between the weld and the bead, resulting in defects. Conventionally, eddy current flaw detection has not been used for defect inspection of welded parts because it is difficult to detect defects in welded parts. [Means for Solving the Problems] As a result of various experiments, the present inventor has found that the noise caused by the change in magnetic permeability described above can be compensated for by the method described below, and that practical inspection of welds can be performed using the eddy current flaw detection method. As a result, the present invention has been made. That is, an AC bridge circuit is constructed of an inspection coil, a comparison coil, and two impedance elements, at least one of which is variable, and the central axis of the inspection coil is oriented perpendicular to the plane of the weld to be inspected. , adjust the impedance element so that the bridge circuit is in a balanced state, then scan the inspection coil in the direction of the weld line, record the unbalanced voltage of the bridge, and determine if a defect in the weld is caused by a change in the impedance of the inspection coil. can be detected as [Function] When an inspection coil is placed close to a welded part, which is a conductor, and an alternating current is passed through the inspection coil, an overcurrent will flow through the welded part. If there is a defect in the weld, the overcurrent is partially blocked and its strength changes. There is a mutual inductive effect between the overcurrent and the test coil, so there is no overcurrent. Changes in the li current appear as changes in the impedance of the test coil. Therefore, an unbalanced voltage is generated in the AC bridge circuit including the test coil as an element. By recording this unbalanced voltage at 1 (11), it is possible to know whether there is a defect or crack in the weld. [Example] An example of the present invention will be described with reference to the drawings. As shown in Fig. 1, the test probe has a test coil 4 wound around the tip of a winding core 3, and a comparison coil 5 wound around the cord 6 side.It is formed by a weld base metal 2 and a weld bead 1. Place the inspection probe on the surface of the weld bead as shown in the figure. In this state, while watching the meter shown in Figure 2, adjust the variable impedance 8 to balance the AC bridge circuit. Next, After adjusting the variable phase shifter 10, the signal generated by the play between the inspection probe and the welding bead 1 is C.
Make it appear only in H2 and CH4. Next, the inspection probe 9 is scanned in a direction perpendicular to the paper surface of FIG. At this time, if there is a deviation of υ1 in the weld, the recorder's CH1 and C1
It appears as a swing of 3 fingers and 1. The constant frequency sine wave alternating current generated by the oscillator in FIG. The unbalanced voltage of the bridge circuit is amplified by an amplifier 3 and sent to a meter and a synchronous detector. To balance the bridge circuit, adjust the resistance value and reactance of the variable impedance element 8 while watching the meter. Next, when the impedance of the test coil 4 changes, the unbalanced voltage of the bridge is amplified by the amplifier 1, and various phase components are received as the output of the synchronous detector. In the case of a real IM VA, two types of mutually orthogonal phase components are tl. Further, the ratio of the increase rate of C1'1 to CH3 and C112 to CH4 is 2:1. These phase components are recorded on a recorder. The results obtained in this example are shown in FIG. 3. In this case, cracks in the welded parts of Cl-11 and Cl-13 clearly appear in the areas indicated by arrows. The winding core of the testing coil can be made of magnetic material or non-magnetic material. In addition, the inspection probe is scanned by using a guide as a guide, and each time the inspection probe moves a certain distance using a rack and pinion structure provided with a guide, an electric signal is emitted, and this is combined with the signal generated by the inspection probe. If they are recorded at the same time, the location of the defect can be determined accurately. [Effects of the Invention] When a welded part is inspected by the method according to the present invention, the inspection probe is small, so the work can be easily carried out in a narrow space. Painted parts and self-welded parts can also be inspected, and the inspection speed is extremely fast, at several hundred meters per day.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing a state in which an inspection probe is arranged in a welded part according to an embodiment of the present invention, Fig. 2 is a block diagram showing the configuration of an apparatus according to an embodiment of the present invention, and Fig. 3 is a chart showing defects in a welded part obtained according to an embodiment of the present invention. 4... Coil for inspection, 5... Coil for comparison, 8...
・Variable impedance element. Applicant's agent Hiroshi Fujiki Procedure? 1 heat l
Official document (Method) June 27, 1985 (Showa 1951) Patent Application No. 76400 2, Name of the invention Method for inspecting welds by eddy current flaw detection 3, Relationship with the famous case in which amendment was made J Patent applicant China X-ray Co., Ltd. Company 4, Agent (zip code 104) June 4, 1986

Claims (1)

[Claims] An AC bridge circuit is constituted by an inspection coil, a comparison coil, and two impedance elements, at least one of which is variable. A method of inspecting welds for defects by adjusting the impedance element so that the bridge circuit is in a balanced state, then scanning the inspection coil in the direction of the weld line and recording the unbalanced voltage across the bridge.