JPH0752131B2 - Fitting stress detection method for double pipe - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to fitting of a corrosion resistant double pipe or the like used for a line pipe for transporting petroleum or natural gas containing a corrosive substance, or a pipe in the chemical industry. Pseudo-acoustic emission (AE) is used to determine whether the fitting stress between the outer pipe and the inner pipe of a compound double pipe (hereinafter simply referred to as double pipe) has a required value.
Said) method for selection.

[Prior Art] A double pipe is a pipe material developed for the purpose of corrosion resistance and cost reduction. Generally, a material having excellent corrosion resistance is used for the inner pipe and carbon steel is used for the outer pipe. As shown in Japanese Examined Patent Publication No. 56-46451, the double pipe uses inner and outer pipes with different components and materials made by separate pipe production lines, and inserts the inner pipe into the heat-expanded outer pipe. After the inner tube is expanded by applying pressure to the inner tube, the inner tube and the outer tube are mechanically fitted by the heat shrinkage of the outer tube. It greatly affects the quality of heavy tubes. When the fitting stress of the double pipe is 10 kgf / mm ² or more, the quality of the double pipe is maintained without the inner pipe coming off or shifting.

[Problems to be Solved by the Invention] Conventionally, as a method of nondestructively measuring the fitting stress of the inner and outer pipes of the double pipe manufactured by such a manufacturing method, Japanese Patent Laid-Open No. 62-828 discloses. Are known. This method measures the fitting stress between the outer pipe and the inner pipe by discriminating the acoustic signal generated when the double pipe is hit by the frequency. In such a conventional method, there are problems that the frequency of the acoustic signal is different depending on the method of holding the double pipe, and the frequency discrimination accuracy is lowered due to noise at the measurement location.

An object of the present invention is to reliably and stably select a quality material having a fitting stress of a double pipe having a required value.

[Means for Solving the Problem] The present invention applies a transmission converter and a reception converter to the outer peripheral surface of a double pipe in which an outer pipe and an inner pipe made of metal materials having different components are fitted to each other, and Is a pseudo AE in the range of 20 to 500 kHz
A signal is transmitted from the transmitting transducer, a waveform propagating through the double tube is received by the receiving transducer, and whether the fitting stress between the outer tube and the inner tube is good or bad is selected according to the duration or area of the detected waveform. This is a method for detecting fitting stress in a double pipe, which is characterized in that

Hereinafter, the details of the present invention will be described with reference to the drawings. As shown in FIG. 1, the pulse signal generated by the pulse generator 1 is converted into an elastic wave, that is, a pseudo AE signal by the transmission transducer 4, and is transmitted to the measured double tube 3 via the couplant 2. It The waveform signal propagating through the double tube 3 to be measured in the direction of the arrow 5 is received by the reception transducer 6 via the couplant 2,
It is converted into an electric signal. This electric signal has, for example, a waveform as shown in FIG. 2 (a), and it 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 the signal processing device 8, and the pass / fail selector 9 determines whether the fit of the inner pipe is good or bad based on the level. Digital measurement is the second
As shown in the figure, it may be performed for any of the waveform duration T and the waveform area S that exceed the predetermined threshold T _h .

An example of the relationship between the frequency of the pseudo AE signal and the SN ratio is shown in FIG. In order to detect the pseudo AE signal with a good SN ratio (SN ratio is 10 dB or more), it is necessary to set the frequency within the range of 20 to 500 kHz.

The transmission converter 4 and the reception converter 6 may be arranged either in the tube axis direction or the tube circumferential direction. An example of the relationship between the distance between the transducers 4 and 6 and the waveform duration T is shown in FIG. A in FIG. 4 shows the case where the fitting stress of the double pipe is insufficient at 2.2 kgf / mm ² , and B shows it at 14.2 kgf / mm ² which is more than the required value. As the inter-transducer distance L increases, the waveform duration T decreases in both cases. If the inter-transducer distance L is less than 0.5 m, the difference between the waveform durations T of A and B is small, and it is difficult to judge pass / fail. Further, when the transducer distance L is 10 m or more, the SN ratio (the ratio of the reception signal and the nozzle) becomes low, which makes it difficult to perform stable measurement. Therefore, the distance L between transducers is 0.5m
As described above, it is desirable that the range is less than 10 m.

FIG. 5 shows an example of the relationship between the fitting stress obtained by the fracture test and the waveform duration T. Since the two have such a proportional relationship, for example, the required fitting stress is 10 kgf / mm ²
In this case, the pass / fail selector 9 may be set so that the case where the waveform duration T is 4 msce or more is passed. Further, since there is a proportional relationship between the fitting stress of the double pipe and the corrugated area S, the pass / fail can be selected also by these. Furthermore, the waveform duration T and the waveform area S of the received pseudo AE signal can be measured by the signal processing device 8, and the fit stress can be measured from the relationship between the fit stress previously obtained and these values.

[Embodiment] Double pipe 2 having outer diameter of 88.9 mm, outer wall thickness of 5.0 mm, outer tube steel type carbon steel, inner tube wall thickness of 1.5 mm, inner tube steel type Inconel 625
For the book, a pseudo AE signal was generated and the waveform duration T of the detected AE signal was detected to determine whether the fit was good or bad. The measurement conditions are a transmission transducer 200 kHz, a reception transducer 200 kHz, a distance between the transducers 1 m, and a pulse transmission frequency 20 Hz.

As a result of judging whether the fitting stress was acceptable or not, the waveform duration T of the No. 1 double tube was 7.5 msec and it was judged to be acceptable. As a result of measuring the fitting stress of the No. 1 double pipe by a destructive test,
It was 18 kgf / mm ² . The waveform duration T of the No. 2 double tube is 2
It was judged to have failed in msec. The fitting stress of the No. 2 double pipe was measured by a destructive test and found to be 4 kgf / mm ² .

EFFECTS OF THE INVENTION According to the present invention, does the fitting stress of the double pipe surely have a required value regardless of the holding method of the double pipe and the noise at the measuring place as compared with the conventional method of discriminating the frequency of the acoustic signal? It is possible to non-destructively determine whether or not the material is good or bad, and it is possible to significantly improve the quality assurance accuracy of the double pipe.

[Brief description 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 reception converter, FIG. 3 is a diagram showing an example of the relationship between frequency and SN ratio, and FIG. FIG. 5 is a diagram showing an example of the relationship between the inter-transducer distance L 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 obtained by a fracture test. 1 ... Pulse generator, 2 ... Contact medium, 3 ... Double tube for measurement, 4 ... Transmitting transducer, 5 ... Arrow, 6 ... Receiving transducer, 7 ... AE measuring instrument, 8 ...... Signal processing device, 9 ・ ・ ・ Pass / fail selector, T _h・ ・ ・ Threshold value, T ・ ・ ・ Waveform duration, S ・ ・ ・
… Wave area.

Claims (1)

[Claims] 1. A pseudo transducer having a frequency in the range of 20 to 500 kHz, which is obtained by applying a transmission converter and a reception transducer to an outer peripheral surface of a double pipe in which an outer pipe and an inner pipe made of metal materials having different components are fitted to each other.
AE signal is transmitted from the transmitting transducer, the waveform propagating through the double pipe is received by the receiving transducer, and the quality of fit stress between the outer pipe and the inner pipe is selected according to the duration or area of the detected waveform. A method for detecting fitting stress in a double pipe, characterized by: