JPS608744A - Ultrasonic flaw detection of welded part of electric welded tube - Google Patents

Abstract

PURPOSE:To detect accurately cold junction defects to discriminate surely whether the welded part of an electric welded tube is good or not, by making the ultrasonic beam having a specific frequency incident on the welded part on the surface of the tube at a specific angle. CONSTITUTION:A probe 3 is set in the direction of a normal 7 of the surface of an electric welded tube 1, and ultrasonic waves 5 are made incident to the depth from the surface of a welded part 2. Ultrasonic waves having a frequency (f) higher than 25MHz and lower than 500MHz are used, and ultrasonic waves are made incident so that an angle (i) of incidence to the normal is wider than 0 deg. and narrower than 12 deg., thereby detecting not only cold junction defects surely but also defects due to Fe, Al, Ca oxides, where mixed oxides are <=10 microns, and a slight penetrator.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ultrasonic flaw detection method that can detect cold weld defects that may occur when electric resistance welding conditions are inappropriate.

(Prior Art) Conventionally, as a method for ultrasonically detecting defects in welded portions of electric resistance welded pipes, a circumferential angle angle flaw detection method as shown in FIG. 1 has generally been used. In FIG.

The ultrasonic beam 5 emitted from the probe 3 enters the tube 1 through the water 4 at an incident angle, is refracted at a refraction angle θ, travels in a zigzag pattern, and is reflected at any defect. The signal returns along the same route and is received by the probe 3.

Conventionally, the frequency f of a probe used in such tube circumferential angle flaw detection is generally 2.25 MHz or more and 5 MHz or less.

Defects in the welded portion 2 are detected by setting the refraction angle θ in FIG. When the tube material is made of steel, the refraction angle θ will fall within the above range if the incident angle is set to 16.0' or more and 27.3° or less. In order to reliably inspect the welded part 2, an electromagnetic induction method is used.
The bath contact part 2 is detected by an optical method, a paint mark method, a magnetic mark method, a visual method, etc., and the probe 3 is made to follow the m contact part 2, and the detection and tracing accuracy of the weld part 2 is also taken into consideration. A plurality of probes 3 are installed at regular intervals.

According to such a conventional ultrasonic flaw detection method, the venetrator present in the welded portion 2 can be reliably detected. In addition, in order to detect flaws in the base metal near the welded part 2 and the bath contact part, as shown in FIG.

At the same time as Venetrator C present in the weld zone 2, low-level inclusions A and B are also detected. However, the most harmful cold weld defects in the welds of ERW pipes are not detected.

Cold weld defects occur when the welding heat input is low, and are defects in which a group of fine oxides, mainly FeO, of several microns or less are included. The presence of cold weld defects in the weld significantly reduces toughness. Such harmful cold weld defects cannot be detected by conventional ultrasonic flaw detection methods, nor can they be detected by other non-destructive testing methods. Therefore, in the past, sample samples were subjected to destructive tests such as fatigue tests or Charpy impact tests.

The presence or absence of cold welding defects was determined by observing the fracture surface under a microscope.

(Object of the Invention) The present invention was made to solve the problems of the conventional method, and uses ultrasonic technology to detect highly harmful cold welding defects that could not be detected by conventional non-destructive inspection methods. The purpose of the present invention is not to accurately detect flaw detection by the flaw detection method and thereby reliably determine the quality of the ERW bath contact part (Structure and operation of the invention). is incident on the outer surface welding part of the control in the range of 00 to 12 degrees in the pipe circumferential direction with respect to the normal to the outer surface of the ERW pipe.

As a result of repeated experiments, the present inventor has discovered that a high S.sub.1 reflection echo can be obtained from a minute cold weld defect by performing flaw detection using the one-probe pulse reflection method using a cylinder frequency. As shown in Fig. 3, the probe 3 was installed in the direction of the normal line 7 of the outer surface of the ERW tube 1, and the ultrasonic wave 5 was incident perpendicularly to the wall thickness direction from the surface side of the welded part 2. . Frequency f is 2.2
Ultrasound in the range of 5-600 MHz was used to investigate the L7-height and noise echo height above the reflection from the cold weld defect.

The results were as shown in FIG.

In other words, frequencies below 5 frequencies f or 20 MHz were hardly reflected back from the cold welding defect, but frequencies above 25 MHz and below 500 M) Iz.

The signal-to-noise ratio was more than 100 dB, and the frequency of -600 MHz was almost never reflected back from the cold welding defect. Further, one frequency f is set to 50 MHz, and as shown in FIG. The height of the reflected echo from the cold weld defect and the height of the noise echo were investigated by changing the position of the probe 3 so that the angle ranged from 00° to 20°.

As shown in Figure 5, the results are as follows:
It was found that the S/N ratio of 2° or less was 10 dB or more, and cold welding defects could be sufficiently detected.

If the S/N ratio is 10 dB or more, stable automatic ultrasonic flaw detection is possible in the same way as conventional angle angle flaw detection, and considering the resolution and S/N ratio, one frequency f is 25 MHz.
Cold welding defects can be reliably detected by using ultrasonic waves in the range of z to 500 MH2 and making the ultrasonic waves incident at an incident angle of 2 o' to 12 degrees with respect to the normal. be.

Weld defects that can be detected by the method of the present invention include, in addition to the cold weld defects described above, contaminating oxides such as Fe-AiL and 0.0 microns or less are present. , oxide defects and slight venetrator.

(Example) Examples of the present invention will be shown below.

As shown in Table 1, the test pieces used were carbon steel electrical resistance welded steel pipes of various outer diameters and wall thicknesses that were welded with a heat input that would cause cold welding defects. FIG. 6 shows an example of an apparatus for implementing the present invention.

In order to reliably detect the weld 2 by setting the incident angle k to 00, the weld 2 is detected by a bath contact detector 8 using a general electromagnetic induction method as shown in Fig. 6, and the weld is traced. Control device 11. The probe 3 is traced by the welding part copying device 12, but considering the detection and tracing accuracy, the probe 3
was swung in the tube circumferential direction by a oscillating motor 9, and flaws were detected in a range of 10 areas on both sides of the welded portion 2. Note that -10 indicates the direction of tube material movement, 13 indicates the ultrasonic flaw detector, and 14 indicates the recorder.0 The frequency f of the probe 3 is 50 MHz, the transducer dimension d is 0.250 inφ, and the focal length is 0.5 inch. A focusing type was used, the flaw detection distance L (see Fig. 3) was set to 3 mm, and the inspection speed υ was 10 m/min. Conventional method and 1
~, the frequency f is 5 MHz, the transducer size d is ],
A flat type probe with Qmmφ and focal length of 60nIn+ was set so that the refraction angle 0 was 45°, and flaw detection was conducted under the same conditions as in the non-inventive example.

Table 1 As a result, as shown in Table 1, with the conventional method, cold welding defects cannot be detected, but with the method of the present invention, all SNN130 d
Flaw detection was possible with B or higher. FIG. 7 shows the flaw detection results (cathode ray tube diagram) of an M5 test piece as an example. A reflected echo from the cold welding defect is observed at a position of '7 mm (L).

The above-mentioned examples relate to carbon steel electric resistance welded pipes, and similar defects can be detected by the method of the present invention in welded parts of other low-alloy steels, stainless steels, and non-ferrous metals. The shape is not limited to pipes, but the same applies to welded parts such as square pipes.

(Effects of the Invention) As detailed above, according to the ultrasonic flaw detection method for welded parts of ERW pipes of the present invention, cold welding defects, which were considered undetectable by conventional non-destructive testing methods, can be reliably detected. This allows the dog to contribute to the inspection of pipe materials used in particularly harsh environments such as cold regions, and can significantly improve the quality assurance of ERW pipes. Therefore, it has become possible to use ERW pipes in fields where seamless pipes have not been used previously.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of conventional pipe circumference angle flaw detection, Fig. 2 is an explanatory diagram of defects that occur in ERW pipes, and Fig. 3 is an illustration of a probe for detecting cold welding defects by the method of the present invention. An explanatory diagram of the arrangement of pipe materials,
FIG. 4 is a chart of cold weld defect detection characteristics when changing the frequency, and FIG. 5 is a chart of cold weld defect detection characteristics when the ultrasonic incident angle is changed. FIG. 6 is a block diagram showing the configuration of an apparatus used in an embodiment of the present invention, and FIG. 7 is a photograph showing the flaw detection results (braun tube pattern) according to the method of the present invention. 1; Advantage 2; Bath contact part 3; Probe 4; Water 5; Ultrasonic beam 7; Outer surface normal 8; Welding part detector 9; Swing motor 10; Illll hardwood direction 11; Welding part copying Control device 2
; Weld spot tracing device 13; Ultrasonic flaw detector 14; Recorder, ; Incident angle U; Refraction angles A, B; Inclusions C; Penetrator L; Detection distance S; Surface echo F; Cold weld defect echo Figure 1 Figure 2 3rd ml Y station f (Mfh) Figure 6

Claims (1)

[Claims] An ultrasonic beam with a frequency of 25 MHz or more and 500 MHz or less is incident on the welded portion of the outer surface of the ERW tube in a range of 06 or more and 12 degrees or less in the tube circumferential direction with respect to the normal to the outer surface of the ERW tube. Ultrasonic flaw detection method for welded parts of ERW pipes.