JPH0560550B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting weld defects in a welded portion of an electric resistance welded pipe.

(Prior Art) Electric resistance welded pipes are manufactured by intensively heating both edges of a steel strip using heat generated by electrical resistance and pressing them together.
Based on FIG. 4, a method for manufacturing electric resistance welded pipes using continuous roll forming will be described.

In this method, a steel pipe is formed and produced from a long steel strip 1. For the steel strip, first break down roll 2 to 6.
It is formed into a U-shape by ~10 sets of horizontal rolls and 3 to 8 sets of vertical rolls, and then, while passing through a unique type of roll called Finpass Roll 3, it becomes circular and at the same time forms a U-shape. Both edges are guided correctly by the fins provided on the roll, leading to the welding process in the form of a so-called open pipe with open seams.

Welding is performed by rapidly and intensively heating only both edges of the formed open pipe using heat generated by an electric current in a welding machine 4, and immediately applying pressure from the side with a squeeze roll 5 to join them.

After welding, the weld bead is scraped off with a cutting tool, and the structure changed by welding is annealed and improved by passing through heat treatment equipment 6. After leaving the heat treatment equipment 6, it is air-cooled for a while, then water-cooled,
It is shaped and cut by a forming roll called a sizer.

The quality of ERW pipes manufactured using the above methods (welding defects) must be guaranteed because conditions such as the butt condition during welding, heat input fluctuations, and pipe manufacturing speed affect the quality (welding defects). .

Currently, quality inspection methods include ultrasonic flaw detection, flatness testing, speculum, Shapey impact testing, and water pressure testing, but it is impossible to perform all of these tests on all products, so inspections using samples are used. becomes. Ultrasonic flaw detection, which is a non-destructive test, and water pressure testing are methods that can perform 100% inspection, but in order to achieve even more advanced quality assurance, technology that detects minute defects that cannot be detected by regular inspection is needed. It has become necessary.

(Problems to be Solved by the Invention) It is desirable that the defect detection technology for improving the ability to inspect the welded quality of electric resistance welded pipes has high detection ability and is 100% non-destructive testing.

The present invention receives acoustic emission (hereinafter referred to as AE) waves generated from welding defects due to thermal stress generated during cooling after welding during pipe manufacturing or subsequent reheating, and detects failure conditions. This is a way to find out.

(Means for solving the problem) Thermal stress is generated in the welded part during cooling after welding or reheating, and the maximum reaches more than the yield stress due to internal temperature conditions. At this time, if there is a defect in the weld, the crack propagates, deformation of the defect, or friction occurs at the crack, resulting in AE. By detecting this AE wave, it is possible to detect abnormalities in the weld in a non-destructive manner.

The present invention was made using this principle,
The gist of this is that after high-frequency welding or local heating using high-frequency waves, the process after the welded part or locally heated part that is the part to be inspected has solidified.
The AE signal generated from the defective part due to thermal stress acting on the part to be inspected is passed through a band elimination filter that removes signals equivalent to and integral multiples of the power source used for welding or local heating, and using liquid as a medium. The present invention provides a method for detecting welding defects in a welded portion of an electric resistance welded pipe, characterized by detecting the welding defect in a non-contact manner and detecting the welding defect from the AE signal.

In other words, in the method for detecting weld defects in a welded part of an ERW pipe, after high-frequency welding or local heating using high-frequency waves, free parts in and around the welded or heated part that is the inspected part are solidified. By restricting shrinkage, it is possible to detect the AE signal generated from the defective part due to thermal stress acting on the inspected part, and it is advantageous to specify the conditions at the time of detection (filter, non-contact using liquid as a medium, etc.) This is designed to detect welding defects.

In the present invention, as a method for detecting AE, a non-contact detection method was adopted, taking into account that the object to be inspected is a pipe and that inspection may be performed even during pipe production.

Specific inspection methods include a continuous inspection method during the pipe making process and during pipe transportation, and a batch inspection method in which the pipe is reheated without moving. In either case, a non-contact detection method is applied.

The non-contact detection method uses a liquid such as water, oil, or glycerin as a medium, and receives AE waves transmitted through the liquid. Specifically, there is a method in which water is jetted toward the pipe from a nozzle equipped with a converter, or a method in which the pipe is submerged in water and a converter is installed inside or on the outside of the container.

On the other hand, methods for generating AE due to thermal stress during the cooling process include a method that utilizes the thermal stress generated during the cooling process after welding, and a method that uses high-frequency induction heating of a local part of the welded part to generate heat during the cooling process. There is a method that uses stress.

Particularly in the latter case, a method that uses heat treatment equipment in the pipe-making process and a method that newly installs a reheating device within the process or offline can be applied.

By employing the method described above, it becomes possible to non-destructively evaluate the welding quality of all ERW pipes.

The present invention will be explained below based on embodiment examples shown in the drawings.

FIG. 1 is a diagram showing an outline of an example of the device,
After a few seconds, the welded steel pipe 7 completes solidification of the molten part and enters a cooling (cooling) process, whereby the high temperature part is gradually cooled.

At this time, the part in question undergoes a compression process, but since it is restrained from the surroundings, free contraction is impossible.
Therefore, thermal stress is generated in the weld, and if there is a defect in the weld, the defect develops into a crack or AE occurs due to friction at the defect.

In order to detect the AE waves generated during this cooling process, a nozzle 9 equipped with a converter 10 is installed on the exit side of the welding machine, and water is jetted from the nozzle toward the pipe. At this time, the AE waves generated from the defect are transmitted through the pipe, water, and nozzle in order, making it possible for the transducer to receive the AE waves.

FIG. 2 shows an example of a signal processing device for the received AE waves.

The AE signal converted into a minute voltage signal by the converter 10 is amplified by the preamplifier 11.
In an environment where there is a lot of flying electrical noise, such as an inspection immediately after welding, it is effective to use a differential amplifier type for the transducer 10 and preamplifier 11. On the other hand, in an environment with little electrical noise, such considerations are effective. is not necessary.

Next, the main voltage signal is connected to the AE device 13,
When high-frequency power is used for welding or local heating, the current flowing through the pipe causes the pipe to vibrate and generate noise, but in this case, only the frequency components that are the same frequency as the power source used, or twice, triple... There is a method of using a band elimination filter 12 to remove the above from the signal.

The electrical signal that has undergone the signal processing described above is connected to the AE device, but in addition to this, noise due to bead cutting, noise due to slipping with the roll, etc. is generated, but unlike the actual AE signal waveform,
Since the waveform becomes gentle, by using an electric filter 14, an envelope processing 15, etc.,
Removal is possible.

The AE signal obtained through such signal processing is processed by the determination device 16 to eliminate harmful defects.
AE signals are identified. As a method for signal processing and determination, there is a method using parameters used in the AE method. Parameters include event, ringdown, energy, peak, amplitude, RMS,
In addition to ASL, rise time, and duration, when applying a method that uses multiple transducers to detect the position of AE occurrence, there is also a parameter called arrival time difference. Furthermore, it is also possible to use a method of recognizing patterns from waveforms.

Using the above method, we can identify AE from defects, and further consider operational conditions such as pipe manufacturing conditions.
If a defect is determined to be harmful, an alarm, conditions and data at that time are output, and the pipe is marked if necessary.

Figure 3 shows an example of the AE waveform actually measured.

In this test, defects were intentionally generated by varying the heat input, and the heat input was successively lowered from excessive heat input until cracking occurred due to insufficient heat input. The upper row shows the change pattern of the heat input.

The lower row shows the envelope processed waveform of the AE signal that has passed through the AE device and each filter, and represents the amplitude. As for the defects, as a result of observing the welding surface with a microscope, it was found that typical welding defects occurred at high and low heat inputs, compared to No. 4, where almost no welding defects were observed. Since defects 1 to 3 have amplitudes that occur spot-wise, AE also occurs spot-wise at a high level.

On the other hand, since defects 5 to 7 are either densely scattered or continuous, AE also occurs continuously with high amplitude. Regarding No. 8, cracks occurred during pipe making, and the cracks appear as they are as AE.

(Effects of the Invention) According to the present invention, it is possible to detect welding defects in welded portions of electric resistance welded pipes by non-destructive 100% inspection and almost in real time. Furthermore, compared to conventional non-destructive testing for local inspection, the inspection accuracy for detecting welding defects in welded parts is improved by inspecting a wider area and the detection ability is not affected by the size of cracks or defects. becomes possible. In addition, since the inspection is performed under conditions higher than the yield stress, it has the advantage of being excellent in detecting truly harmful defects.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an embodiment of the present invention, and FIG.
The figure is an explanatory diagram of the configuration of the AE measurement system, and Figure 3 is a diagram showing the structure of the AE measurement system.
FIG. 4, which is a diagram of an example of AE measurement data, is a schematic explanatory diagram of the forming process up to welding or heat treatment of an electric resistance welded pipe. 1: Long steel strip, 2: Breakdown roll,
3: Fin pass roll, 4: Welding machine, 5: Squeeze roll, 6: Heat treatment equipment, 7: Steel pipe, 8: Welding section, 9: Nozzle, 10: AE converter, 11: Preamplifier, 12: Band area Menation filter, 13: AE device, 14: Filter, 15:
Envelope processing, 16: Judgment device.

Claims (1)

[Claims] 1 After high-frequency welding or local heating using high-frequency waves, the AE signal generated from the defective part due to thermal stress acting on the inspected area is detected in the process after the welded area or locally heated area that is the inspected area has solidified. It is characterized by detecting welding defects from the AE signal through a band elimination filter that removes signals equivalent to and integral multiples of the power source used for welding or local heating, and in a non-contact manner using liquid as a medium. A method for detecting weld defects in a welded section of an ERW pipe.