JPS6144345A - Eddy current flaw detection of welded pipe - Google Patents

Abstract

PURPOSE:To make it possible to easily detect a minute welding flaw, by forming a welded pipe so that the welded part thereof is present at a corner place or smallest radius place and passing said welded pipe through a piercing type eddy current flaw detector to perform the inspection of the welded part. CONSTITUTION:A welded pipe having a circular cross-sectional area is deformed by a forming roll group to be formed into a welded pipe having a predetermined shape other than a circle (e.g., a welded pipe 4c having a rectangular cross- sectional area or flat welded pipe). At this time, a welded part 5c is provided so as to be present at a corner part in the case of the welded pipe having a rectangular cross-sectional area and provided so as to be present at a smallest radius part in the case of the flat welded pipe. This welded pipe 4c is passed through a cylindrical eddy current flaw detector 3A to perform the eddy current flaw detection of the welded part 5C. Because the gap between the welded part 5C and the coil 2A of the eddy current flaw detector 3A becomes narrower than the other part, an eddy current flows unequally and mostly concentrated to the welded part 5C. Therefore, if the welded part 5C has a flaw, even a minute flaw largely exerts effect on the flow of the eddy current and a large detection signal can be obtained.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to the eddy current flaw detection method (eddy current flaw detection method) of metal pipes, and more specifically, to the inspection of welded parts of welded pipes whose cross section has a shape other than a circle. This paper relates to the eddy current flaw detection method. In particular, it is preferable that the present invention be applied to the inspection of welded parts of flat welded tubes, which are water pipes in heat exchangers used in automobile radiators and the like.

Conventional technology A method for manufacturing a welded pipe whose cross section is a shape other than a circle (for example, a rectangular shape, or a field track shape in which opposing parallel parts are connected in a semicircle like the above-mentioned flat welded tube) is as follows: If high-frequency welding is used, the following steps may be required. The metal strip material to be welded is formed into a tube (circular cross section) using a group of forming rolls, the joint is heated by a heating coil or contact of a high-frequency welding machine, and the material is pressed into a squeeze roll (pressure roll). The mating surfaces of the heated metal strips are pressed against each other to continuously weld them into a cylindrical tube.Next, the outer bead of this welded tube is cut with a bead cutter, etc.), and the welded tube is cleaned. A tube with a predetermined cross-sectional shape (shape other than a circle) is formed using a group of forming rolls.

These steps are carried out continuously, and in particular, continuous production is possible if a coil-shaped metal strip is used as the raw material (for example, as described in Japanese Patent Application No. 58-41823 filed by the present applicant).
(See the specification of No. 4, Detailed Description of the Invention section, and Prior Art section). In such a welded pipe manufacturing method, the inspection (defect detection) of the welded part is usually carried out using an eddy current flaw detector using a self-comparison type through-type deep flaw element (coil) in front of the group of forming rolls after welding or This is done by placing it at the rear (as in FIG. 5 or 6). 5 and 6 are cross sections perpendicular to the central axis of the welded tube (that is, the direction of movement of the welded tube), showing the coil bobbins IA, IB and the coils 2A, 2.
Penetrating type deep wound element 3A consisting of B.

3B and welded tubes 4A and 4B are shown.

Incidentally, a cross section in the longitudinal direction of the penetrating flaw detectors 3A and 3B is shown in FIG. 7, and as such a coil bobbin,
For example, the one proposed in Japanese Utility Model Application Publication No. 55-103562 can be used.

Problems to be Solved by the Invention Figure 5 shows a case where a welded part 5A of a circular cross-section welded pipe 4A before forming is inspected by the eddy current flaw detection method, but as shown in Figure 8, the eddy current I Since it flows evenly over the entire circumference of the tube 4A, it is easy to detect minute dents and surface scratches other than the welded parts that do not pose a quality problem, and it is difficult to detect minute weld defects with a defect length of 1+u or less. Moreover, although FIG. 6 shows a case where the welded part 5B of the flat welded pipe 4B after forming is being inspected,
In addition to the fact that it is difficult to detect minute weld defects as in the case of the circular cross-section welded tube described above, the noise generated by minute vibrations of the welded tube in the vertical direction makes detection of minute weld defects even more difficult.

Means for Solving the Problems The present invention provides an eddy current flaw detection method that can easily detect minute defects in welded parts of welded pipes whose cross section has a shape other than a circle. This is done by the eddy current flaw detection method for welded pipes, which is characterized in that the welded part is formed so that the welded part is at the corner point or the minimum radius point, and the welded pipe is passed through a through-type eddy current flaw detector.

Forming in the eddy current flaw detection method according to the present invention is performed, for example, during the forming process from a circular cross-section welded pipe 4A (Fig. 5) to a flat welded pipe 4B (Fig. 6) as explained in the conventional technique. The rectangular cross-section welded pipe 4C shown in Figure 1 has a welded part 5C.
In particular, it is desirable to maintain the metal tube manufacturing method proposed by the applicant in Japanese Patent Application No. 118234/1982.
As shown in the figure, although the shape is almost the same as that of the welded pipe in FIG. 6, the welded portion 5D may be located at the minimum radius.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to the accompanying drawings.

Materials to be welded: brass, copper, aluminum, stainless steel,
Strips of weldable metals such as steel, low-alloy steel, etc. (e.g. plate *
0.15 to 0.08mm, 47i width 29mc7)i Copper strip) is prepared, and the joining end is transformed into a longitudinal cylindrical shape by a group of forming rolls to form a tube. The ends to be joined are heated by a welding coil or a high-frequency induction welding contact, and a squeeze roller is used to apply pressure so that the joined ends abut against each other for welding. The welded tube has a circular cross section (Figure 5). Beads (burrs) generated at the weld are removed using a bead cutter, and welding spatter and cutting chips adhering to the surface of the welded pipe are cleaned and removed using a cleaning device. Then, the circular cross-section welded pipe 4A (FIG. 5) is deformed by a group of forming rolls in order to form it into a welded pipe having a predetermined shape other than a circle (for example, the flat welded pipe 4B shown in FIG. 6). At this time, according to the present invention, a predetermined shape is formed through the welded pipe 4C, which has a rectangular cross section with rounded corners, and the welded portion 5C is located at the corner, as shown in FIG. Eddy current testing of the welded portion 5C is performed by passing this rectangular cross-section welded tube 4C through a conventional cylindrical eddy current flaw detector 3A (FIGS. 5 and 7) as shown in FIG. In this case, the coil 2A of the eddy current flaw detector 3A and the welded part 5
Since the gap with C is narrower than in other parts, the eddy current l flows unevenly as shown in FIG. 2, and is most concentrated in the welded part 5C. Therefore, if there is a defect in the welded portion 5C, even if it is minute, it will greatly affect the flow of the generated eddy current and a large detection signal will be obtained. On the other hand, the flow of eddy current I spreads in areas other than the weld, causing scratches and
It becomes difficult to detect dents, etc. Therefore, in the eddy current flaw detection method according to the present invention, signals other than weld defects can be suppressed to a greater extent than in conventional methods, the S/N ratio is improved, and minute weld defects with a defect length of 11 mm or less can be detected. In the case of Fig. 1, since the cross section of the welded pipe 4C is almost square and the coil 2A is circular, the gap with the coil 2A is similarly narrow in areas other than the corners where the welded part 5C is located, and vortices are generated. There is a possibility that the current (2) will be concentrated at the corner as shown in Figure 2, and scratches and dents will be detected in this area. However, even in such cases, the S/N ratio is improved compared to conventional eddy current testing (Figures 5 and 6). If so, the S/N ratio is further improved.

In this case, the eddy current flaw detector is placed in the group of forming rolls, and the forming roll also functions as a guide roll.
The effects of vibrations in welded pipes are hardly a problem. Then, the rectangular cross-section welded pipe 4C is further deformed by a group of forming rolls, and the flat welded pipe 4 has a predetermined welded part 5B in a flat part.
B is manufactured.

The eddy current flaw detection method of the present invention can be applied to a flat welded pipe 4 as shown in FIG.
It is sufficient that the welded portion 5D is located at the minimum radius point at D, and furthermore, it can be applied to welded pipes with cross-sectional shapes such as elliptical and oval shapes.

Furthermore, according to the eddy current flaw detection method of the present invention, it is possible to detect a welding defect in the case where a peeling part 6 is formed in the welded part 5C due to insufficient welding strength during forming the welded pipe 4c as shown in FIG. Can be done.

Effects of the Invention As described above, when performing an eddy current inspection on a welded part of a welded pipe, if the welded part is located at a corner of the cross-sectional shape of the welded pipe other than a circle or at the minimum radius, a welding defect will be detected. The S/N ratio of the signal to be detected can be increased, and inspection can be performed reliably and easily.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a rectangular welded pipe and an eddy current flaw detector during the eddy current flaw detection method according to the present invention, and FIG. FIG. 3 is a schematic diagram illustrating eddy currents generated in a cross-sectional welded pipe; FIG. 3 is a cross-sectional view of a flat welded pipe where the weld is at the minimum radius; FIG. FIG. 5 is a cross-sectional view of a circular cross-section welded pipe and an eddy current flaw detector during conventional eddy current flaw detection; FIG. 6 is a partial perspective view of a welded pipe according to the conventional eddy current flaw detection method; Fig. 7 is a cross-sectional view of the flat welded pipe and the eddy current flaw detector during the
8 is a longitudinal cross-sectional view of the eddy current flaw detector shown in FIGS. IA, IB...Coil bobbin, 2A, 2B...-Coil, 3A, 3B...-Eddy current flaw detector, 4A...Circular cross-section welded pipe, 4B...-Flat welded pipe, 4C-Rectangular cross-section welded Pipe, 4D...-Flat welded pipe, 5A, 5B, 5C, 5D... Welded part.

Claims (1)

[Claims] 1. In eddy current flaw detection of a welded pipe manufactured through a step of forming a welded cylindrical pipe whose welded portion is parallel to the central axis of the cylindrical pipe so that its cross section has a shape other than a circle, An eddy current flaw detection method for a welded pipe, characterized in that the welded pipe is formed so that the welded portion is located at a corner point or a minimum radius point, and the welded portion is inspected by passing it through a penetrating eddy current flaw detector. 2. The eddy current flaw detection method for welded pipes according to claim 1, wherein the welded pipes are thin-walled tubes welded by high-frequency welding.