Device for Automatically Determining the Class and Marking of Cast Iron Pipes
Abstract Generated abstract
This paper describes an automatic device for classifying and marking cast iron pipes during production according to their minimum wall thickness, as required by standards that distinguish reject, LA, A, B, and thick walled classes. The system uses a radioisotope thickness meter based on backscattered Cs-137 gamma radiation detected by a scintillation detector, with the resulting voltage analyzed through amplifiers, discriminators, logic storage, and class decoders. The device records the discriminator state corresponding to the minimum measured thickness during inspection and sends the appropriate command to a marking mechanism that drills coded hole patterns on the pipe end face. Experimental results report a class determination sensitivity of at least 2% of the inspected thickness, discriminator threshold stability of 0.2%, and an inspection time of 30 seconds for a five meter pipe.
Full Text
Device for Automatic Determination of the Class and Marking of Cast-Iron Pipes
G. I. Lopandin
(Submitted by the scientific seminar of the Research Institute of Electronic Introscopy)
According to GOST, the pipes produced, depending on wall thickness, are divided into classes: reject, LA, A, B, and thick-walled.
The device is intended for objective marking of the class of pipes in the production process in accordance with the minimum value of the wall thickness of each pipe. The wall-thickness sensor in this device is a radioisotope meter [1] operating on the principle of recording the backscattered $\gamma$-radiation of the isotope Cs$^{137}$ with a scintillation detector containing a load $RC$ circuit. The integration time constant is 1 sec.
The cases possible during pipe inspection may be characterized by the graph shown in Fig. 2. The voltage curve at the output of the scintillation detector repeats the graph shown in Fig. 2 with a certain scale factor, and is written as
$$ U = f(l), $$
where
$l$ is the position of the detector relative to the start of inspection. The sensor voltage $U=f(l)$ is analyzed by the class-determination device, and in accordance with the result of the analysis a command is issued to the marking device.
Fig. 1. Cases possible during pipe inspection
Fig. 2. Dependence of thickness on detector position for the cases B, A, LA, reject
The block diagram of the device is shown in Fig. 3. Gamma quanta from radiation sources 1, located in container 2, strike the pipe 3 being inspected. Part of the quanta is reflected by the pipe material and is registered by scintillation detector 4. The voltage developed in the load \(RC\)-circuit of the detector is fed through amplifier 5 and through cathode followers 6--10 to the inputs of discriminators 11--15. The response thresholds of the discriminators are set by level-setting devices 16--20. Logic circuit 21 stores the state of the discriminators corresponding to the minimum voltage during inspection of the pipe. In accordance with the selected block diagram, after completion of the pipe-inspection process five discriminator states are possible, each of which corresponds to one of five classes. Class decoders 22 serve to ensure that each of the five states
Fig. 3. Block diagram of a device for determining the class and marking cast-iron pipes
| Class | Marking |
|---|---|
| scrap | + + + |
| LA | + + |
| A | + |
| B | + + |
| thick |
Fig. 4. Pipe marking depending on class
of the discriminators (i.e., each class) has its own output circuit connected with marking device 23. The pipes are marked by drilling the end face of the pipe. To designate the classes, marks formed by combinations of three holes on the end face of the pipe are used (Fig. 4).
As experimental studies have shown, the sensitivity of the class-determination device is no worse than 2% of the thickness being inspected. The stability of the discriminator threshold is 0.2%. The time required to inspect one five-meter pipe is 30 sec.
References
- L. K. Tatochenko. Radioactive Isotopes in Instrument Engineering. Atomizdat, Moscow, 1961.