JPH0752132B2 - Double pipe fitting stress detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a corrosion resistant double pipe (hereinafter simply referred to as a double pipe used for a line pipe for transporting petroleum or natural gas containing a corrosive substance or a pipe in the chemical industry). The quality of whether the fitting stress between the outer and inner pipes (called double pipe) has the required value,
The present invention relates to a detection device for selecting by a pseudo acoustic emission (hereinafter referred to as AE) method.

[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 Patent Publication No. 56-46451, the double pipe uses an inner pipe and an outer pipe made of different pipe manufacturing lines and having different components and materials, and the inner pipe is heated and expanded. After the inner tube is inserted and pressure is applied to expand the inner tube, the inner tube and outer tube are mechanically fitted by the heat shrinkage of the outer tube. Has a great influence on the quality of the double pipe. 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.

Conventionally, Japanese Patent Laid-Open No. 62-828 is known as a method for nondestructively measuring the fitting stress of the inner and outer pipes of the double pipe manufactured by such a manufacturing method. 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.

[Problems to be Solved by the Invention] In such a conventional method, there arises a problem 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 the vibration noise of the measurement place. Was there. Also, as a method of destructive measurement, measure the residual strain of the inner pipe when a strain gauge is attached to the inner surface side of the inner pipe of the pipe material taken from the end of the double pipe and the outer pipe is cut with a saw etc. However, it can be calculated, but there is a problem that the fitting stress at the center of the pipe cannot be measured.

In view of the above-mentioned problems of the prior art, the present invention provides a double-tube fitting stress measuring device for surely selecting non-destructively and stably a good or bad material for which the fitting stress of the double tube has a required value. The purpose is to do.

[Means for Solving the Problems] A dual pipe fitting stress measuring device of the present invention for achieving this object is a transmission converter for converting a signal of a pulse generator into a pseudo AE signal, and a double pipe for propagating. Receiving converter that converts the plate wave signal into an electrical signal, AE measuring device that performs envelope detection processing on the signal of the receiving converter, signal processing device that performs A / D conversion processing on the signal of the AE measuring device, and signal processing It is characterized by comprising a pass / fail judgment device for comparing one or more signals among signals corresponding to the waveform duration and the plate wave area of the device with the set signal.

[Embodiment] An embodiment of the present invention will be described below in detail with reference to the drawings.
As shown in FIG. 1, the electric pulse signal (FIG. 2 (a)) generated by the pulse generator 1 is converted into a pseudo AE signal via the contact medium 2 by the return converter 4, and the two signals for measurement are measured. A plate wave is generated in the heavy pipe 3. The plate wave propagating in the direction of arrow 5 is received by the reception converter 6 via the couplant 2,
It is converted into an electric signal. This electric signal has a waveform as shown in FIG. 2 (b), and the AE measuring device 7 performs envelope detection processing on this electric signal to obtain a waveform as shown in FIG. 2 (c). The envelope detection waveform is taken into the A / D converter in the signal processing device 8, the AE waveform parameter is digitally measured at a sampling time of 100 μsec, and the pass / fail determination unit 9 determines whether the fit of the inner and outer tubes is good or bad based on the level. As shown in FIG. 2, the digital measurement may be performed for any of the AE waveform parameters of the waveform duration T or the waveform area S that exceeds a predetermined threshold T _h .

Next, an embodiment using the device of the present invention will be described. FIG. 3 shows an example of the relationship between the fitting stress obtained by the fracture test and the waveform duration T. Since both are in a proportional relationship as shown in this figure, for example, the required fitting stress is 10 kg.
In the case of f / mm ² , the pass / fail judgment unit 9 may be set so as to pass when the waveform duration T is 4 msec or more.
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.

The arrangement of the transmitting converter and the receiving converter may be on the tube axis or the tube circumferential direction, or on the tube inner surface or the tube outer surface. Fourth
The figure shows an example of the relationship between the distance between the transducers 4 and 6 and the waveform duration. When the distance L between the transducers increases, the waveform duration T
Becomes smaller, and it is necessary to keep the distance between transducers constant when evaluating fit stress. When evaluating pipe materials having different inter-transducer distances L, it is necessary to obtain the relationship between the inter-transducer distance and the waveform duration in advance and make corrections using the calibration curve.

Double pipe outer diameter: 88.9mmφ, outer pipe wall thickness: 5.0mm, outer pipe steel type: carbon steel, inner pipe wall thickness: 1.5mm, inner pipe steel type: Inconel 625 (trade name), pipe material Length: For two 1.5 m double tubes, generate a pseudo AE signal to detect the waveform duration T,
The quality of the fit stress was judged. Measurement conditions are electric pulse voltage V: 10V, converter frequency f: 200kHz, distance between converters L: 1
m, pulse repetition frequency f _p : 20 Hz, threshold value T _h : 0.1 V. 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. No.
The fitting stress of the double pipe of No. 1 was measured by a destructive test and found to be 18 kgf / mm ² . The waveform duration T of the No. 2 double tube was 2 msec and it was judged as a failure. 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 judge whether or not the material is good or bad, and 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 plate wave waveform detected by a receiving transducer, and FIG. 3 is a relationship between fit stress obtained by a destructive test and waveform duration T. FIG. 4 is a diagram showing an example of the relationship between the transducer distance and the waveform duration. 1 ... Pulse generator, 2 ... Contact medium, 3 ... Double tube,
4 ... Transmission converter, 5 ... Detection plate wave propagation direction, 6 ...
Reception converter, 7 ... AE measuring instrument, 8 ... Signal processing device, 9
...... Pass / fail judgment device, T _h・ ・ ・ Threshold value, T ・ ・ ・ Waveform duration, S ・ ・ ・ Waveform area, L ・ ・ ・ Distance between converters, V ・ ・ ・ Electrical pulse voltage, f ・ ・ ・ Converter frequency, f _p …… Pulse repetition frequency.

Claims (1)

[Claims] 1. A transmission converter (4) for converting a signal of a pulse generator (1) into a pseudo AE signal, and a reception converter (6) for converting a plate wave signal propagating through a double tube into an electric signal. , AE measuring device (7) for envelope detection processing of signal of receiving converter (6)
And a signal processing device (8) for A / D converting the signal of the AE measuring device (7) and at least one signal corresponding to the waveform duration and the waveform area of the signal processing device (8). A double pipe fitting stress detection device comprising a pass / fail judgment device (9) for comparison with a set signal.