JPS62828A - Detecting of fitting stress of double pipe - Google Patents

Abstract

PURPOSE:To surely and stably detect the fitting stress of a double pipe to be measured by subjecting the sound generated from the double pipe when the double pipe is striken by a hammer or the like to frequency discrimination. CONSTITUTION:The acoustic signal generated from the double pipe 7 to be measured when the double pipe 7 is striken by a striking device 8 such as hammer is detected by an acoustic signal detector 9 such as microphone and after the signal is converted to an electric signal, the detection signal is amplified by an amplifier 10. The signal of the specific acoustic frequency range generated according to the joining condition of the inside and outside pipes of the double pipe is extracted from the amplifed electric signal by a frequency discriminator 11 such as band-pass filter which allows the passage of only the electric signal of the specific acoustic frequency range. The detectiveness or non-defectiveness of the joint between the inside and outside pipe is discriminated and selected by an acceptance and reject selector 12 by which the fitting stress of the inside and outside pipe is detected.

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention detects the fitting stress of the inner and outer tubes of a two-layered steel tube (hereinafter referred to as a double tube) consisting of inner and outer tubes of different steels using an acoustic testing method. It's about how to do it.

(Prior art) In general, double pipe manufacturing methods for the purpose of corrosion resistance involve manufacturing lines for the inner and outer pipes, and the inner and outer pipes of different steels are joined by methods such as shrink fitting, but when joining the inner and outer pipes, The fitting stress greatly affects the quality of the double pipe.

Conventionally, the method of detecting the stress of fitting between the inner and outer tubes of a double tube is to transmit ultrasonic waves in the thickness direction of the inner and outer tubes, and to judge the quality of the fit based on the attenuation of the transmitted ultrasonic waves based on the scattering of the ultrasonic waves at the interface between the inner and outer tubes. It is known from Destructive Inspection Handbook (4th edition) P, 478.

In such a conventional method, it is difficult to identify only the bonded state because defect detection of the inner and outer tube base materials is performed at the same time as the bonded state inspection. Furthermore, if oil, water, etc. are present in the gap between the inner and outer tube layers, it may be mistaken as a good joint. In addition, there have been problems such as difficulty in inspection unless the transmitting and receiving probes are positioned opposite each other and their contact with the steel pipe is stabilized.

This state will be explained in detail with reference to FIG.

FIG. 2 shows the principle of a double tube fitting stress detection method using a conventional ultrasonic transmission method. In the explanatory diagram, 1 is an outer tube, 2 is an inner tube, 3 is an interface between the inner and outer tubes, 4 is a receiving probe, 5 is a transmitting probe, and 6 is a couplant. In this state, ultrasonic waves are generated from the transmitting probe 5 and transmitted through the couplant 6 to the inner tube 2.
Inject ultrasonic waves into the The incident ultrasonic waves propagate inside the tube in the direction of arrow S, and the outer tube 1. Although the ultrasonic waves are detected by the receiving probe 4 via the couplant 6, attenuation occurs in the ultrasonic waves detected by the receiving probe 4 due to the bonded state of the inner and outer tube interfaces 3.

The fitting stress between the inner and outer tubes is detected based on the strength of the transmitted ultrasound. However, the opposing positions of the transmitter/receiver probe 5, the contact conditions of the probes with the inner and outer tubes, defects in the inner tube quality, and the medium in the gap between the inner and outer tube layers affect the amount of ultrasound transmitted, so the evaluation of the inner and outer tube joints may be misdiagnosed. Ru.

(Problems to be Solved by the Invention) An object of the present invention is to reliably and stably detect the fitting stress of a double pipe.

(Means for solving the problem) This invention is a method for detecting the fitting stress of a double pipe by frequency-discriminating the sound generated by the double pipe when the double pipe to be measured is struck with a hammer or the like. .

The details of the present invention will be explained below with reference to FIG. When the double pipe 7 to be measured is subjected to an impact with a striking device 8 such as a hammer, the acoustic signal generated from the double pipe 7 to be measured is detected by an acoustic signal detector 9 such as a microphone and converted into an electrical signal. , the detection signal is amplified by an amplifier lO. The amplified electrical signal is passed through a frequency discriminator 11 such as a band-pass filter that allows only electrical signals in a specific acoustic frequency range to pass through, which extracts signals in a specific acoustic frequency range that are generated depending on the state of the double-pipe-internal-interior-tube joint, and determines pass/fail. A sorter 12 selects whether the inner and outer tubes are joined properly or not according to job.

Note that the striking method used in the striking device 8 is not particularly limited and may be any method such as mechanical striking using an air cylinder or the like, or striking using electromagnetism such as electromagnetic ultrasonic waves.

(Function) A shock is applied to the double pipe 7 to be measured by the impact device 8, and the sound generated from the double pipe 7 is detected by the acoustic signal detector 9.
The signal is amplified by an amplifier 10, and a signal in a specific acoustic frequency range generated depending on the adhesive condition between the inner and outer double tubes is discriminated by a frequency discriminator 11 to detect the fitting stress between the inner and outer tubes.

For example, a specific acoustic frequency range generated by the adhesion status of the inner and outer tubes of a double pipe to be measured is frequency-discriminated using high- and low-pass filters or a spectrum analyzer, and the fitting stress of the inner and outer tubes is detected. be.

As a specific method for detecting fitting stress, for example,
When the fitting stress is within a desired range, the specific acoustic frequency range that can be discriminated is frequency-discriminated using high and low band filters, and when the specific acoustic frequency range is discriminated, the fitting stress is passed, and when it is not discriminated, the fitting stress is passed. Fail. Another method is to frequency-analyze the detected and amplified acoustic signal using a spectrum analyzer or the like, and obtain the fitting stress from the relationship between the acoustic frequency range determined in advance and the fitting stress.

(Example) Metal round bars for two double pipes to be measured of steel pipe outer diameter 89.1φ, outer pipe wall thickness 6.0 m, steel type carbon steel, inner pipe wall thickness 1.5 cage, steel type stainless steel. The sound generated by the impact was detected.

On the other hand, the frequency discriminator uses a frequency range of 2.70 to 2.75 k generated by the double pipe to be measured with a stress exceeding a predetermined fitting stress.
As a result of setting the Hz and determining the pass/fail of the fitting stress, it was determined that the double tube with &1 passed, and the double tube with flat 2 failed.

In addition, as a result of measuring the fitting stress of each double pipe, the flatness l is 2
0'q/lta'', mu2 was 0yu/simp2.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment according to the present invention, and FIG. 2 is a schematic sectional view showing a conventional technique.

Claims (1)

[Claims] A method for detecting fitting stress in a double-pipe tube, characterized by detecting fitting stress in the inner and outer tubes by frequency-discriminating acoustic signals generated when a steel tube with a double-layer structure composed of inner and outer tubes of different steel types is struck.