JP2000346831A - Ultrasonic flaw detection method and ultrasonic probe for plastic pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic flaw detection method and an ultrasonic probe with which a deep portion can be inspected, the detection sensitivity of a defective is good, the proximity of a surface can be sufficiently flaw- detected, a micro defective in a fusion portion between end surfaces of plastic pipes can be easily and certainly found. SOLUTION: Ultrasonic wave with frequency of 0.5-2.0 MHz is radiated, an refraction angle θ2 of the ultrasonic wave at a boundary with a body to be detected is larger than its incident angle θ1. For performing this ultrasonic flaw detection method, this ultrasonic probe 9 comprises a transducer 10 for radiating the ultrasonic wave with frequency of 0.5-2.0 MHz and a wedge 11 made of material with sound speed slower than that of the body to be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic flaw detection method and an ultrasonic probe for a plastic pipe for detecting a defect in a plastic pipe, particularly, a defect in a welded portion between end faces of the plastic pipe by ultrasonic waves. .

[0002]

2. Description of the Related Art Conventionally, metal pipes such as cast iron pipes and steel pipes have been used as transport pipes for distributing clean water, sewage water, hot springs, muddy water and the like because of their high strength. And such transport pipes have been in operation for 30 years, unless otherwise damaged or ruptured.
Used for as long as 40 years. However, metal pipes such as cast iron pipes and steel pipes have a problem in durability because the inner wall surface is easily corroded by clean water, sewage water, hot springs, muddy water, etc., and the outer wall surface is easily corroded by rainwater, chemical substances, etc. is there. In addition, since it has a large specific gravity and does not have flexibility, there is also a problem that laying work requires a great deal of time and labor. Therefore,
In recent years, plastic tubes made of vinyl chloride, phenol, polyethylene, and the like have been used to solve such problems.

[0003] Pipes for flowing water, sewage, hot springs, muddy water and the like are constituted by connecting a large number of such plastic pipes. In the case of plastic pipes, flanges are formed and fastened with bolts and nuts. In addition to a method of joining by joining together, a method of joining by joining the end faces of the plastic tubes by heat is common and widely used.

[0004] As a joining method by such heat fusion, FIG.
First, the heater plate 2 is brought into contact with the end faces of the plastic pipes 3a and 3b to be melted, and then the end faces of the plastic pipes 3a and 3b are brought into contact with each other and joined. A butt fusion method is known.
When performing butt fusion, it is necessary to control various setting conditions such as a fusion temperature, a fusion pressure, and a fusion time with high accuracy.

[0005] As a method of inspecting a defect at a fusion portion between the end faces of the plastic tubes 3a and 3b, for example, an X-ray projection method of projecting an X-ray to the fusion portion and inspecting the defect with an internal image, a fusion method, or the like. A penetrating inspection method in which an inspection solution is applied to a bonding portion and a defect is inspected based on a penetration state, an ultrasonic inspection method in which ultrasonic waves are radiated to a fusion portion and a defect is inspected by a reflected wave, and the like are considered. Among them, the X-ray projection method uses an X-ray, so that the inspection apparatus becomes large, and cannot be implemented in a place such as a residential area where people are crowded. Penetrant inspection can only inspect defects that open to the surface to see the penetration of the solution.

[0006] On the other hand, the ultrasonic flaw detection method uses an ultrasonic probe 4 composed of a transducer 5 and a wedge 6 shown in FIG.
A wedge 6 of 5.0 MHz is made of polyethylene. In the ultrasonic flaw detection method, it is not necessary to remove the fluid from the inside of the plastic pipe, but conventionally, since the ultrasonic wave is largely attenuated and does not propagate far, the thick plastic pipes 3a and 3b have deep fusion parts. No flaws can be detected in any part. Also, increasing the angle of incidence theta ₁ for applying ultrasonic s the fusing surface 7, the incident loss increases, the detection sensitivity of the defect is deteriorated. Further, since the beads 8a and 8b are formed, there is a limit to the approach of the ultrasonic probe 4 to the fused portion, and an undetectable area u is formed from the surfaces of the plastic tubes 3a and 3b to a predetermined depth.

[0007]

As described above, in the X-ray projection method, the inspection apparatus becomes large and cannot be performed in a place where people are densely located, such as a residential area. Can only be tested, and there are a number of limitations in performing the test. In addition, the ultrasonic flaw detection method has a problem that flaw detection cannot be performed to a deep part, the defect detection sensitivity is poor, and a flaw-detection-impossible area u is generated near the surface. For this reason, conventionally, it has not been possible to easily and reliably find a minute defect in the fusion portion between the end faces of the plastic tubes 3a and 3b.

The present invention has been made to solve such a conventional problem, and its object is to detect flaws in deep portions, to have good defect detection sensitivity, and to sufficiently detect flaws near the surface. It is an object of the present invention to provide an ultrasonic flaw detection method and an ultrasonic probe for a plastic tube that can easily and surely find a minute defect in a fusion portion between end faces of the plastic tubes 3a and 3b.

[0009]

In order to achieve the above object, an ultrasonic flaw detection method for a plastic tube according to the present invention emits ultrasonic waves having a frequency of 0.5 to 2.0 MHz, and emits ultrasonic waves at a boundary with a subject. it is characterized in that to increase the refraction angle theta ₂ than the incident angle theta ₁ of the ultrasound.

The ultrasonic probe 9 according to the present invention is for performing the above-described ultrasonic flaw detection method, and emits ultrasonic waves having a frequency of 0.5 to 2.0 MHz as shown in FIG. It is characterized by comprising a transducer 10 and a wedge 11 made of a material whose sound speed is lower than that of the subject.

Although the attenuation of the ultrasonic wave is smaller as the frequency is lower, the frequency of the ultrasonic wave is 0.5 to 2.0 MHz, preferably 0.5 to 2.0 MHz, considering that the detection limit defect size is の of the wavelength. 75-1.75 MHz, particularly preferably 1.75 MHz.
0 to 1.5 MHz.

The detection limit defect size d can be expressed as d = λ / 2 = c / (2ν) where λ is the wavelength, ν is the frequency, and c is the sound speed. The sound speed of a plastic tube made of polyethylene is Assuming that the frequency of the ultrasonic wave is 1.0 MHz, the detection limit defect size d is as follows: d = c / (2ν) = 2200 / (2 × 1.0 × 10 ⁶ ) = 1.1 × 10 ^-3 , which means that a defect of about 1 mm can be detected.

As described above, the frequency of the ultrasonic wave is set to 0.5 to
By setting the frequency to 2.0 MHz, the attenuation of the ultrasonic wave is reduced as compared with the related art, so that it is possible to detect a flaw in a deep portion of the fusion joint of the plastic tube and to improve the defect detection sensitivity.

When the angle of refraction θ ₂ is made larger than the angle of incidence θ _{1 of the} ultrasonic wave at the boundary with the subject, that is, when a wedge 11 made of a material whose sound speed is lower than that of the subject is used,
As shown in FIG. 3, the incident angle θ _{1 is} smaller than that of the related art.
However, a sufficiently large refraction angle θ ₂ can be obtained. Thus, by reducing the incident angle theta _1, it is possible to reduce the incidence loss can be a good detection sensitivity of defects. Further, the probe 9 is connected to the beads 8a and 8b.
Close to the limit, the plastic tube 3
The undetectable area u from the surfaces a and 3b can be greatly reduced.

Since the apparent diameter of the transducer 10 is reduced by the refraction of the ultrasonic wave, the width w of the ultrasonic beam is reduced as shown by the oblique lines in FIG.
Will spread more vertically. Therefore, in practice, it is possible to detect even a defect near the surface.

In the case of a plastic pipe made of polyethylene having a sound speed of 2200 m / s, a fluorine resin having a sound speed lower than that of polyethylene, for example, a sound speed of 1500 m / s
Polytetrafluoroethylene is (PTFE: Teflon (registered trademark)) by using a wedge 11 made of, it is possible to increase the refraction angle theta ₂ than the incident angle theta ₁ of the ultrasound. However, the material of the wedge 11 is not limited to PTFE, but may be a tetrafluoroethylene / hexafluoropropylene copolymer (FEP: NEOFLON FEP (registered trademark)).
Etc.), tetrafluoroethylene / perfluorovinyl ether copolymer (PFA: Teflon PFA (registered trademark))
Etc.), or any material having a lower sound velocity than the subject.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an ultrasonic flaw detection method and an ultrasonic probe for a plastic pipe according to the present invention will be described in detail with reference to experimental examples of ultrasonic flaw detection and the operation and effects thereof.

[0018] 1. Experimental probe for internal defect detection The following three types of ultrasonic probes were manufactured. The wedge of each ultrasonic probe has a shape as shown in FIG. 4 and dimensions as shown in Table 1. 1) manufactured by probe A60-1.5 transducer A548S (Nippon Panametrics Co.) ultrasonic frequency [nu 1.5 MHz wedge polytetrafluoroethylene (PTFE: Teflon) refraction angle theta ₂ 59 ° of the subject ( 2) Probe A50-1.0 Transducer V539SM (manufactured by Nippon Panametrics Co., Ltd.) Ultrasonic frequency ν 1.0 MHz Wedge Polytetrafluoroethylene (PTFE: Teflon) Refraction angle θ ₂ with subject 50 ° (relative to polyethylene) 3) Probe A40-1.0 Transducer V539SM (manufactured by Nippon Panametrics Co., Ltd.) Ultrasonic frequency ν 1.0 MHz Wedge Polytetrafluoroethylene (PTFE: Teflon) Refraction with subject Angle θ ₂ 42 ° (vs. polyethylene)

[0019]

[Table 1]

As shown in the subject Figure 5, a circular hole 13 having a predetermined diameter at a predetermined position of the side surface of the polyethylene plate (high density polyethylene),
A large number of samples 15 and 16 were formed as a subject 12. That is, the upper surface 12a of the polyethylene plate was assumed to be the surface of the plastic tube, and the bottom surfaces 13a, 14a, 15a, 16a of the circular holes were assumed to be planar circular defects generated in the plastic tube. Therefore, for example, 30 mm from the upper surface 12a of the polyethylene plate
The bottom surface 15a of the φ3.0 circular hole formed at the position
This corresponds to a φ3.0 plane circular defect formed at a depth of 30 mm from the surface of the plastic tube.

Experimental Method Each probe was placed on the upper surface 12a of a polyethylene plate as an object, and moved in the axial direction of the circular holes 13, 14, 15, 16 to determine whether or not each planar circular defect could be detected. I checked. As shown in FIG. 6, since the ultrasonic wave s does not hit the plane circular defect 17 perpendicularly, most of the ultrasonic wave s does not return to the transducer 10 and most of the ultrasonic wave s detected by returning returns to the plane circular defect 17. Is a diffracted wave (end echo) generated at the end 17a.

Experimental Results The detection limit diameter of the planar circular defect 17 at each depth was as follows for the above three types of probes. 1) Probe A60-1.5 Depth less than 20 mm Detection limit diameter 1.0 mm 2) Probe A50-1.0 Depth less than 30 mm Detection limit diameter 1.0 mm Depth less than 40 mm Detection limit diameter 3.0 mm 3) Probe A40-1.0 Depth less than 40mm Detection limit diameter 1.0mm Depth less than 50mm Detection limit diameter 4.0mm Depth 60mm Detection limit diameter 5.0mm

As described above, by using the above three types of probes, the plane circular defect 17 can have a detection limit diameter of 1.0 mm and a depth of 40 to 5 mm up to a depth of 40 mm.
At 0 mm, the detection limit diameter is 4.0 mm and the depth is 50-60 m
In the case of m, flaw detection was possible at a detection limit diameter of 5.0 mm.

[0024] 2. Surface Defect Detection Experiment Subject As shown in FIG. 7, a slit 24 having a predetermined depth was formed at a predetermined position from a side surface of a polyethylene plate (high-density polyethylene) having a step formed in the length direction, thereby obtaining a test object 18. That is, each step 19, 20, 21, and 2 of the polyethylene plate
Upper surfaces 19a, 20a, 21a, 22a, 23 of 2, 23
a was assumed to be the surface of the plastic tube, and the slit 24 was assumed to be a surface defect generated in the plastic tube. So, for example,
The slits 24 in the 16 mm high step 20 of the polyethylene plate correspond to surface defects formed from the surface of the plastic tube to a depth of 2 mm.

Experimental Method Upper surfaces 19a, 20 of each step of a polyethylene plate as a test object
a, 21a, 22a, and 23a, the probe A60-1.5 is placed, and the distance from the slit 24 is set to 10 mm or 15 mm.
Was set, and it was confirmed whether or not each surface defect 25 could be detected. As shown in FIG. 8, since the ultrasonic beam actually has a predetermined width w, flaw detection can be performed up to near the surface above the sound axis s.

Experimental Results According to the probe A60-1.5, when the distance to the slit 24 was set to 10 mm, the distance to the slit 24 was set to 15 mm up to a surface defect having a depth of 2 mm. , A surface defect with a depth of 3 mm could be detected.

As described above, by using the probe A60-1.5, the width of the beads 8a and 8b is reduced to 20 m.
In the case of m, a defect having a depth of 2 mm or more can be detected, and when the width of the beads 8a and 8b is 30 mm, a defect having a depth of 3 mm or more can be detected.

[0028] 3. Defect Height Measurement Experiment Experimental Method The probe A40-1.0 was placed on the upper surface 12a of the polyethylene plate which was the subject 12 used in the internal defect detection experiment, and the circular holes 13 and 14 were formed as shown in FIG. , 15,1
6 is moved by a small distance in the axial direction, and each planar circular defect 17 is moved.
At the upper end 17a and the echo at the lower end 17b. Then, the minute movement distance x was measured.

The height h of the calculation method flat circular defect 17, if the small moving distance x, the refraction angle and theta _2, can be written as h = x / tanθ _2.

Experimental Results According to the probe A40-1.0, for a plane circular defect 17 having a diameter of 4.0 mm or more and a depth of less than 30 mm, the height h was measured within an error range of ± 0.5 mm. We were able to. Regarding the planar circular defect 17 having a diameter of less than 4.0 mm, the echo at the upper end 17a and the echo at the lower end 17b could not be clearly distinguished, and the height h could not be measured.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a state in which end faces of plastic tubes are joined by a butt fusion device.

FIG. 2 is a cross-sectional view of a main part showing a state in which a fused part of a plastic tube is detected by a conventional ultrasonic probe.

FIG. 3 is a cross-sectional view of a main part showing a state in which the ultrasonic probe according to the present invention detects a flaw in a fused portion of a plastic tube.

FIG. 4 is a plan view of a wedge of an ultrasonic probe used in an experiment.

FIG. 5 is a view showing each surface of an object used in an internal defect detection experiment.

FIG. 6 is a sectional view of a main part showing a state where an internal defect of a plastic tube is detected by the ultrasonic probe of the present invention.

FIG. 7 is a view showing each surface of an object used in a surface defect detection experiment.

FIG. 8 is a cross-sectional view illustrating a state where a surface defect of a plastic tube is detected by the ultrasonic probe according to the present invention.

FIG. 9 is a cross-sectional view of a main part showing a method for measuring the height of an internal defect in a plastic tube using the ultrasonic probe of the present invention.

[Explanation of symbols]

 3a, 3b Plastic tube 9 Ultrasonic probe 10 Transducer 11 Wedge

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G047 AA08 AB01 BB02 BC08 BC09 EA05 EA08 GB27 4F211 AG08 AG21 AJ03 AM02 AM23 TA01 TC11 TD07 TW39 5D019 AA01 AA22 FF05 GG01 GG03

Claims (8)

[Claims] 1. An ultrasonic flaw detection method for a plastic tube, which emits an ultrasonic wave having a frequency of 0.5 to 2.0 MHz. 2. An incident angle of an ultrasonic wave at a boundary with a subject.
θ₁Angle of refraction θ _TwoIs characterized by increasing
Ultrasonic flaw detection of plastic tubes. 3. A plastic tube which emits an ultrasonic wave having a frequency of 0.5 to 2.0 MHz and has a refraction angle θ ₂ larger than an incident angle θ _{1 of the} ultrasonic wave at a boundary with a subject. Ultrasonic inspection method. 4. An ultrasonic probe comprising a transducer for emitting ultrasonic waves having a frequency of 0.5 to 2.0 MHz and a wedge. 5. An ultrasonic probe comprising a transducer and a wedge made of a material whose sound speed is lower than that of a subject. 6. An ultrasonic probe comprising: a transducer that emits an ultrasonic wave having a frequency of 0.5 to 2.0 MHz; and a wedge made of a material whose sound speed is lower than that of a subject. 7. The ultrasonic probe according to claim 5, wherein the wedge is made of a fluorine resin. 8. The ultrasonic probe according to claim 7, wherein the fluorine resin is polytetrafluoroethylene (PTFE).