JPH0375536A - Method for detecting joint stress of duplex tube - Google Patents

Abstract

PURPOSE:To judge whether the joint stress of a duplex tube has a required value or not without destruction and to make it possible to select pass or fail by bringing a transmitting transducer and a receiving transduce into contact with the outer surface of the duplex tube, transmitting a simulated AE signal in the range of 20 - 500 kHz, and receiving the simulated AE signal which is propagated through the duplex tube. CONSTITUTION:A pulse signal which is generated in a pulse generator 1 is transduced into an elastic wave, i.e. a simulated AE signal in a transmitting transducer 4. The signal is transmitted into a duplex tube 3 to be measured through a contact medium 2. The simulated AE signal which is propagated in the duplex tube 3 in the direction of an arrow 5 is received by a receiving transducer 6 through a contact medium 2 and transduced into an electric signal. The electric signal undergoes envelope detection by an AE measuring device. The digital value is measured by a signal processing device 8. The pass or fail of the joint of the inner and outer tubes is judged by a pass-or-fail selecting device 9.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention is applied to the fitting of corrosion-resistant double pipes used for line pipes for transporting oil and natural gas containing corrosive substances, or for piping in the chemical industry. A pseudo-acoustic emission (A
The present invention relates to a detection method for sorting by the method (referred to as E).

[Prior Art] A double pipe is a pipe material developed for the purpose of corrosion resistance and cost reduction; numerically, the inner pipe is made of a material with excellent corrosion resistance, and the outer pipe is made of carbon steel. The double pipe is special public Sho 5B-464.
As shown in Figure 51, an inner tube and an outer tube with different components and materials made on separate tube manufacturing lines are used, the inner tube is inserted into the heated and expanded outer tube, and pressure is applied inside the inner tube. After expanding the inner tube, the inner tube and outer tube are mechanically fitted together by thermal contraction of the outer tube, but the fitting stress when fitting the inner and outer tubes greatly affects the quality of the double-walled tube. . When the fitting stress of the double tube is 10 kgf/+n+++2 or more, the inner tube does not come off or shift, and the quality of the double tube is maintained.

[Problems to be Solved by the Invention] Conventionally, a method for non-destructively measuring the fitting stress between the inner and outer tubes of a double-walled tube manufactured by such a manufacturing method is disclosed in Japanese Patent Laid-Open No. 62-828. Are known. This method is
The fitting stress between the outer tube and the inner tube is measured by distinguishing the acoustic signals generated when the double tube is hit by frequency. Such conventional methods have problems such as the frequency of the acoustic signal being different depending on how the double tube is held, and the accuracy of frequency discrimination being lowered due to noise at the measurement location.

The object of the present invention is to reliably and stably select good or bad materials to determine whether the fitting stress of a double pipe is at a required value.

[Means for Solving the Problems] The present invention applies a transmitting transducer and a receiving transducer to the outer circumferential surface of a double tube in which an outer tube and an inner tube made of metal materials of different components are fitted, and the frequency A pseudo AE multiplied signal in the range of 20 to 500 kHz is transmitted from the transmitting converter, the signal propagated through the double tube is received by the receiving converter, and the waveform of the received pseudo AE multiplied signal is used to differentiate between the outer tube and the inner tube. This is a method for detecting fitting stress in double pipes, which is characterized by determining whether the fitting stress in the pipes is good or bad.

Hereinafter, details of the present invention will be explained with reference to the drawings. As shown in FIG. 1, a pulse signal generated by a pulse generator 1 is converted into an acoustic wave, that is, a pseudo AE multiplied signal, by a transmission converter 4, and is transmitted to a double pipe 3 to be measured via a couplant 2. Ru. Pseudo A propagating in the direction of arrow 5 through the double pipe to be measured 3
The E-multiplied signal is received by the reception converter 6 via the couplant 2 and converted into an electrical signal. This electric signal has a waveform as shown in FIG. 2(a), for example, and can be envelope-detected by the AE measuring device 7 to obtain a waveform as shown in FIG. 2(b). These AE waveforms are digitally measured by a signal processing device 8, and based on the level, a pass/fail selector 9 judges whether the fit between the inner and outer tubes is good or bad. Digital measurement is
As shown in FIG. 2, the waveform duration T, the waveform area S, and the waveform maximum amplitude value Vp exceed a predetermined threshold Th.
You can do this for any of the following.

An example of the relationship between the pseudo AE multiplied signal frequency and the SN ratio is shown in FIG. Pseudo AE double signal SN ratio good < (SN ratio is 10dB
Above) In order to detect it, it is necessary to set the frequency in the range of 20 to 500 kHz.

Further, the transmitting transducer 4 and the receiving transducer 6 may be arranged in either the tube axis direction or the tube circumferential direction. An example of the relationship between the distance between both transducers 4.6 and the waveform duration T is shown in FIG.

A in Figure 4 indicates that the fitting stress of the double pipe is 2.2 kgf.
/mm2 is insufficient, B is 14.2kgf/n
This is the case where un2 is greater than or equal to the required value.

As the distance between the transducers increases, the waveform duration T becomes shorter in both cases. If the distance between the transducers is less than 0.5 m, the difference in waveform duration T between A and B is small, making it difficult to judge whether the product is good or bad. Furthermore, if the transducer distance is 10 m or more, the SN ratio (ratio of the received signal to the nozzle) becomes low, making it difficult to perform stable measurements. Therefore, the distance between transducers is 0.5
It is desirable that the distance be within a range of not less than m and less than 10 m.

FIG. 5 shows an example of the relationship between the fitting stress and the waveform duration T determined by a destructive test. Since the two are in a proportional relationship, for example, the required fitting stress can be set to 10 kgf.
/am2, the waveform duration T is 4 m5ec
The pass/fail selector 9 may be set so that the above cases are accepted. In addition, there is a proportional relationship C between the fitting stress of the double pipe and the waveform area S or the waveform maximum amplitude vp, so
Based on these factors, it is also possible to determine pass/fail. Furthermore, the received pseudo AE multiplied signal waveform duration T, waveform area S
Alternatively, the waveform maximum amplitude value Vp can be measured by the signal processing device 8, and the fitting stress can be measured from the relationship between the fitting stress determined in advance and these multiple values.

[Example double tube outer diameter 88.9QIIllφ, outer tube wall thickness 5.0mm
, for two double-walled tubes with an outer tube steel of carbon steel, an inner tube wall thickness of 1.5 mm, and an inner tube steel of Inconel 625, a pseudo AE multiplied signal is generated, the detected AE multiplied signal waveform duration T is detected, and the fit is determined. I decided whether it was good or bad. Measurement conditions are transmitter converter 200k
Hz, reception converter 200kHz, converter open circuit 1111m
, the pulse oscillation frequency is 20Hz.

As a result of determining whether the fitting stress was acceptable or not, the waveform duration T of the No. 1 double tube was determined to be 7.5 m5ec, which was determined to be acceptable. The fitting stress of the double tube No. 1 was measured by a destructive test and was found to be 18 kgf/rnm2. N
o. The waveform duration T of the double tube of 2 was 2 m5ec and was judged to be a failure. The fitting stress of No. 2 double tubes was measured by a destructive test and was found to be 4 kgf/mm2.

[Effects of the Invention] According to the present invention, compared to the conventional method of frequency-discriminating acoustic signals, it is possible to reliably check whether the fitting stress of the double tube has the required value regardless of the method of holding the double tube or the noise at the measurement location. It is possible to non-destructively determine whether the material is acceptable or not, and to sort out passable or defective materials, greatly improving the accuracy of quality assurance for double-walled pipes.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a specific example of the present invention, FIG. 2 is a diagram showing a waveform detected by a receiving transducer, FIG. 3 is a diagram showing an example of the relationship between frequency and SN ratio, and FIG. 4 is a diagram showing an example of the relationship between frequency and SN ratio. Converter open circuit ll! FIG. 5 is a diagram showing an example of the relationship between IL and the waveform duration T, and FIG. 5 is a diagram showing an example of the relationship between the fitting stress and the waveform duration T determined by a destructive test. DESCRIPTION OF SYMBOLS 1...Pulse generator, 2...Coupling material, 3...Double tube for measurement, 4...Transmission transducer, 5...Arrow, 6
... Reception converter, 7.-AE measuring device, 8. Signal processing device, 9. Pass/fail selector, Th... Threshold value, T
...Waveform duration, S...Waveform area, Vp...Waveform maximum amplitude value.

Claims (1)

[Claims] 1. A transmitting transducer and a receiving transducer are applied to the outer peripheral surface of a double tube in which an outer tube and an inner tube made of metal materials with different components are fitted, and a pseudo AE signal with a frequency in the range of 20 to 500 kHz is generated. The signal transmitted from the transmitting transducer and propagated through the double tube is received by the receiving transducer, and the quality of the fitting stress between the outer tube and the inner tube is determined based on the waveform of the received pseudo AE signal. Features a method for detecting fitting stress in double pipes.