JPH10253598A - Method for inspecting fusion joint of plastic pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a highly accurate reliable inspection, which can not be expected through visual view inspection, by finding a reference echo scope capable of discriminating an echo on the inner surface by ultrasonic flaw detection method and then subjecting a fusion joint to ultrasonic flaw detection under identical conditions. SOLUTION: Flaw detecting conditions, especially acoustic frequency, discriminable an echo with sufficiently high sensitivity on the inner face 111 at a plastic pipe part 11 are set by reflection pulse method employing a vertical probe 3. It can be set easily by varying the frequency of an ultrasonic flaw detector continuously and grasping the frequency when an echo e becomes large sufficiently at a time t0 =2T/C, where T is the thickness of the plastic pipe and C is the sound velocity in a plastic medium. Ultrasonic flaw detection is then performed under conditions being set while moving the vertical probe 3 on the outer surface of a fusion joint 4 and an echo scope is displayed. If an echo is present in the echo scope at a time t=2T/C, such a judgement is made that a defect exists at a joint directly under that flaw detection face.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting an insertion type fusion spliced portion of a plastic tube by an ultrasonic flaw detection method.

[0002]

2. Description of the Related Art When joining plastic pipes, a male part of a heating jig heats and softens the inner peripheral surface of a joint receiving port, and a female part of the jig heats and softens the outer surface of an insertion opening of a pipe. After being removed from the jig, the pipe insertion may be quickly inserted into the socket of the joint and fusion-bonded. Inspection of this fusion-bonded part is usually performed by visual inspection, It is often the case that a defect is overlooked.

[0003] Inspection of internal defects of a welded joint of a metal pipe by an ultrasonic flaw detection method is generally performed. The internal defects of the welded joint of this metal pipe are various, such as poor fusion of the groove surface, poor fusion of the beat multi-layer pipe, poor penetration of the inside, poor penetration of one side, entrapment of slag, vertical cracks, lateral cracks, etc. In addition, since the eco-characteristics are different depending on the defect form, it is necessary to perform the inspection many times by changing the incident angle and frequency of the ultrasonic wave from the flaw detector.

[0004]

As is well known, in a fusion spliced part of a plastic pipe, sound wave propagation attenuation in a plastic medium is remarkable and directivity is weak, so that an ecological effect on defects is small. Because of this, the S / N ratio is poor, and it is said that it is difficult to inspect the fusion spliced portion of the plastic tube by ultrasonic testing in terms of accuracy.

However, as for the fusion splicing portion of the plastic plate, the transmitting probe is arranged on the front side of the joining portion, and the receiving probe is arranged on the back side of the joining portion, and ultrasonic waves are transmitted through the joining portion. The amount of attenuation is measured to determine the quality of the fusion joint from the ultrasonic attenuation rate (Plastic Processing Technology Handbook New Edition No. 76 published by Nikkan Kogyo Shimbun).
3 to 765).

[0006] However, it is difficult to inspect the internal defect of the plastic tube fusion joint by the ultrasonic transmission method due to the arrangement of the receiving probe. By the way, the internal defect of the insertion type fusion bonding part of the plastic pipe is a bonding defect at the interface, and the defect surface and the inner and outer surfaces of the pipe are in the same direction,
Simple. Therefore, even if the ultrasonic wave propagation property of the medium and the ultrasonic reflectivity at the defect surface are inferior to the welded joint of the metal pipe, if this disadvantage can be complemented by the simplicity of the defect, the plastic pipe It is considered that the internal defect of the insertion type fusion bonding part can be inspected with sufficient accuracy.

SUMMARY OF THE INVENTION In view of the foregoing, it is an object of the present invention to be able to inspect internal defects of a plug-type fusion splicing part of a plastic pipe with sufficient accuracy by an ultrasonic flaw detection method.

[0008]

According to the present invention, there is provided a method for inspecting a plastic pipe fusion spliced joint by ultrasonic flaw detection. A standard eco-scope that can determine the inner eco-economy of a standard sample of the size to be inspected by ultrasonic flaw detection is obtained, and the fusion spliced part is subjected to ultrasonic flaw detection under the same conditions as these ultrasonic flaw detection conditions. The ultrasonic inspection is performed by a reflected pulse vertical inspection method.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of a plastic pipe fusion joint as an inspection object in the present invention. As shown in FIG.
The male part of the heating jig 2 is press-fitted into the receiving end of the jig, and the end of the plastic pipe 12 is press-fitted into the female part of the jig.
The inner peripheral surface of the receiving port and the outer peripheral surface of the end of the plastic tube 12 are heated to a softening point or a melting point or higher, and then the joint 11 and the plastic tube 12 are quickly removed from the jig 2 as shown in FIG. Then, the end of the pipe 12 is inserted into the socket of the joint 11 and fusion-bonded.

FIG. 2 shows another example of a plastic pipe fusion joint to be inspected according to the present invention. A receiving port 110 is previously formed at one end of a plastic pipe 11, and a receiving port of one plastic pipe 11 is formed. The insertion opening 120 of the other plastic tube 12 is fusion-bonded to the 110 by heating and inserting in the same manner as described above. The internal defect in the insertion-type fusion bonding part of these plastic tubes is usually caused by poor fusion at the bonding interface, and the form of the defect is parallel to the inspection surface where the probe contacts, that is, the outer surface of the fusion bonding part. This is a planar defect. Thus, when the test object is metal, such a planar defect can be detected with high sensitivity by the pulse reflection vertical method.

That is, a vertical flaw detector is arranged on the flaw detection surface immediately above the planar defect, and the piezoelectric vibrator of the flaw detector resonates at a specific frequency by applying a pulse voltage, and its mechanical vibration energy is reduced. Is incident on the inspection object, vertically propagated as ultrasonic waves into the inspection object, the transmitted ultrasonic waves are vertically incident on the planar defect, and the reflected sound waves are received by the vertical flaw detector. The ultrasonic wave is converted into an electric signal by the piezoelectric vibrator, the position of the defect is obtained from the time difference between the pulse and the received signal, and the size of the defect is obtained from the size of the received signal. In this case, when the frequency is high, the wavelength of the ultrasonic wave is short, and the scattering and reflection at the crystal grain boundaries in the propagation medium are likely to occur, and the attenuation of the propagated sound wave is large. Although lower, the reflectivity at the defective surface is lower. The frequency also affects the directivity and coherence of the propagating ultrasonic waves. Furthermore, the speed of sound and the pulse width are also S
/ N ratio. However, if the test object is a metal, it is possible to detect with high sensitivity over a sufficiently wide frequency range because of the excellent low attenuation of the propagating ultrasonic waves of the metal and the high reflectance at the defective portion.

On the other hand, among the internal defects of the insertion type fusion splicing part of the plastic tube to be inspected in the present invention, even if the same planar defect as described above, the plastic medium has a high damping property, and Since the reflectivity is low and the S / N ratio is poor due to the low sound velocity, it is difficult to determine the ultrasonic flaw detection conditions, particularly the frequency, that enable detection with sufficient sensitivity.

However, the method of inspecting the internal defect of the plug-type fusion spliced part of the plastic pipe by the ultrasonic flaw detection method according to the present invention is based on the position of the internal defect (poor fusion at the bonding interface) with respect to the flaw detection surface, In order for the direction to match the position and direction of the tube inner surface with respect to the tube outer surface (flaw detection surface),
Focusing on the fact that if the former flaw detection is performed under effective ultrasonic flaw detection conditions for the latter, the effectiveness of the former will be maintained and the inspection of internal defects of the former will be possible. , Internal defects can be easily detected.

First, as shown in FIG. 3A, a plastic tube portion 11 [in the case of the sample shown in FIG.
In the case of the sample shown in FIG.
Is set by using the vertical flaw detector 3 and by the reflection pulse method, flaw detection conditions that can determine the echo on the inner surface 111 of the tube with sufficiently high sensitivity, in particular, the sound wave frequency. That is, assuming that the speed of sound in a plastic medium is c and the thickness of the plastic tube is T, a Braun tube (CR
T), the time t = 2T / c, as shown in FIG.
Sets a frequency at which a sufficiently high eco-e can be displayed. This setting is easy because the frequency of the ultrasonic flaw detector can be continuously changed and the frequency at which the echo at time t ₀ = 2T / c becomes sufficiently large can be grasped. The ultrasonic flaw detector having a frequency range of 0.5 to 20 MHz and a sound speed range of 1000 to 3000 m / sec can be used.

The setting of the ultrasonic inspection conditions for the plastic portion by the reflected pulse vertical inspection method may be performed on a plastic pipe or a joint before joining the plastic pipe or a standard sample of a size to be inspected. Next, as shown in FIG. 3C, while the vertical flaw detector 3 is moved using the outer surface of the fusion bonding portion 4 as a flaw detection surface, ultrasonic flaw detection is performed under the flaw detection conditions set for the plastic pipe portion.
Display the eco-scope.

In this eco-scoop, the time t = 2
At T / c, if there is an echo, it is determined that there is a defect at the joining position immediately below the flaw detection surface, and if there is no echo, it is determined that there is no defect. In the above, it is effective to use a couplant such as water, oil, glycerin, etc., in order to make the vertical flaw detector and the test object or the standard sample come into contact with each other without any gap and to efficiently transmit ultrasonic waves.

In the present invention, any of longitudinal waves and transverse waves can be used for the ultrasonic waves in the vertical ultrasonic flaw detection. In particular, in the case of the transverse waves, the vibration direction becomes parallel to the planar defect at the bonding interface,
This is advantageous because it can sufficiently detect even a peeled surface that has been in close contact. Ideally, the movement of the flaw detector on the outer surface of the fusion-bonded portion is performed so as to cover the entire outer surface, but the circumferential direction may be partially inspected. It is desirable to conduct inspections at at least eight places at equal intervals.

The indication of the scope using the outer surface of the fusion joint as a flaw detection surface is such that the flaw detector is moved on the flaw detection surface, and the flaw detector position when an echo exceeding a certain height is obtained is obtained. The display may be a two-dimensional display or a C-scope display. In the present invention, the ultrasonic flaw detector has a digital type,
Both analog types can be used, and a general-purpose ultrasonic thickness gauge can be used.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The sample to be inspected is a plastic tube fusion joint shown in FIG.
hard PVC pipe with a pipe wall thickness of 7 mm
A hard vinyl chloride joint having an outer diameter of 135 mm and a wall thickness of 10 mm was used. Samples prepared by fusion welding by an expert and those fused by a beginner were prepared.

For each joint in each sample, a reference eco-scope was determined by which the echo on the inner surface of the joint could be determined by ultrasonic testing. For the flaw detector, a vertical flaw detector manufactured by Nippon Matek with a diameter of 8 mm is used. For the ultrasonic flaw detector,
A full digital ultrasonic flaw detector Eco-Graph 1080 manufactured by Nippon Matek Corporation was used. The obtained reference ultrasonic flaw detection conditions were a frequency of 4 MHz and a sound speed of 2100 m / sec, and the above-mentioned time t ₀ was 9.5 μsec.

The flaw detector is moved onto the outer surface of the fusion spliced part of each sample, and inspected under the above-mentioned standard ultrasonic flaw detection conditions to score.
As a result, when the sample was fusion-bonded by an expert, the eco at the time t did not substantially appear, but in the sample fusion-bonded by a beginner, the eco was significantly reduced at the time t. Appeared. After the ultrasonic flaw inspection, a fracture water pressure test was performed. As a result, the fracture water pressure value was 7.
The original tube part was broken at 6 MPa, but the fusion spliced interface was broken at a breaking water pressure value of 3.5 MPa in the sample fusion-bonded by a beginner, confirming the reliability of the inspection result.

[0022]

According to the present invention, it is possible to detect the internal defect of the insertion type fusion spliced part of the plastic pipe by the ultrasonic flaw detection method, and it is possible to perform a highly accurate and highly reliable inspection which cannot be expected in the appearance inspection. Further, it is possible to estimate the internal pressure strength from the rise of the eco-friendly, and it is possible to guarantee the appropriate quality maintenance of the plastic pipe fusion joint.

[Brief description of the drawings]

FIG. 1 is a view showing an example of a plastic pipe fusion joint to be inspected according to the present invention.

FIG. 2 is a view showing another example of a plastic pipe fusion joint to be inspected according to the present invention.

FIG. 3 is a view used to explain a method of inspecting a fusion spliced portion of a plastic pipe according to the present invention.

[Explanation of symbols]

11 plastic tube or joint or standard sample of size to be inspected 12 plastic tube 3 vertical flaw detector 4 fusion spliced part

Claims (2)

[Claims] 1. A method for inspecting an insertion type fusion spliced part of a plastic pipe by ultrasonic flaw detection, wherein an echo on the inner surface of the plastic pipe or a joint or a standard sample of a size to be inspected is determined by ultrasonic flaw detection. A method for inspecting a fusion spliced part of a plastic pipe, wherein a feasible reference eco-scoop is determined and the fusion spliced part is subjected to ultrasonic flaw detection under the same conditions as the ultrasonic flaw detection conditions. 2. The method according to claim 1, wherein the ultrasonic inspection is performed by a reflected pulse vertical inspection method.