JPH044383A - Examination system of earthquake-proof piping holding device in service period - Google Patents

Abstract

PURPOSE:To improve the maintenance efficiency and the reliability of examina tion by installing an accelerometer on the main body of a mechanical snapper. CONSTITUTION:In examination system during the service period of an earth quake-proof holding device used in an atomic power plant, a mechanical snapper 3 is installed between a piping 1 and a fixing wall 2 in an atomic furnace stor ing container A. In the mechanical snapper 3, when a surface pressure acting to a ball screw 4 reaches a specific value and a ball unit 5 is moved, a mechani cal vibration is generated to the mechanical snapper 3 and a piping holder system. To detect this vobration, a small accelerometer is installed. As a result, the vibration can be detected in a simple device. Furthermore, no variation of the index value owing to a drift is generated, and a highly reliable detection can be carried out constantly.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an in-service inspection system for seismic piping support devices used in nuclear power plants. [Conventional technology]

For example, piping in a cooling system in a nuclear power plant is thin and reaches high temperatures, so the piping support device is required to be earthquake resistant. As an earthquake-resistant piping support device, a reaction force is not generated by static displacement such as thermal displacement of the piping, but when an impactful excitation force is applied due to an earthquake, a rigid support action is applied to reduce the response amplitude. Mechanical snubbers exhibiting these characteristics are known in the art. FIG. 2 schematically shows the internal structure of the mechanical snubber 3. Static displacement, such as thermal displacement of piping, is allowed by the movement (stroke) of the pole nut 5 as the pole screw 4 rotates. Furthermore, when a sudden excitation force is applied due to an earthquake, the pole screw 4 rotates at high speed, causing the rotation transmission ball 6 to move outward, and the brake 23 to be pressed to the left in the figure, creating a restraining force on the piping. It has a structure that allows The mechanical snubber 3 must not restrict the thermal displacement of the piping, or the mechanical snubber 3 must not restrict the thermal displacement of the piping 1 when the rotational resistance of the hole screw 4 increases under certain conditions in conjunction with other factors. It becomes a factor. Based on the knowledge so far, when the pipe moves at extremely low speed, the rotational resistance of the ball screw 4 may exceed the rotational torque generated by the component force of the axial load of the mechanical snubber 3. However, when the ball screw 4 rotates due to some stimulus, the function of the mechanical snubber 3 is restored again. The installation location of the mechanical snubber is difficult to access during operation, and if the mechanical snubber does not operate smoothly for some reason, it will put an excessive load on the piping system. It is necessary to confirm the soundness of the system by conducting inspections during its service life to ensure that it is operating smoothly and following displacement. To briefly explain the conventional confirmation method using FIGS. 4 and 5, this example uses a displacement detector 14 fixed on a pedestal 13.
15 is a piping lug, and 16 is a piping displacement detection box. As shown in FIG. 5, the internal structure of the displacement detector 14 is such that a spindle 18 is slidably fitted into a cylindrical body 17, and when the spindle 8 moves in the Y direction due to thermal displacement of the pipe 1, the coil A strain gauge 2 attached to the cantilever 20 bends the cantilever 20 via a spring 19 and measures the degree of bending of the cantilever 20 at that time.
It was detected by I, and from this the amount of displacement of the piping was known.

[Problem to be solved by the invention]

Displacement detectors using strain gauges as described in 1. may become difficult to move due to sticking at the sliding part of the spindle, misalignment of the detector, or deterioration of the detector due to irradiation with high radiation equivalents. Values became unstable, and especially fluctuations in indicated values due to drift significantly impaired reliability. Furthermore, since the mechanism was not simple, there was a risk of mechanical failure, and maintenance was troublesome and required a lot of labor. The present invention has been made in view of the conventional situation described in 1. with the aim of simplifying the apparatus to reduce the need for improvement in maintainability and to improve the reliability of inspection.

[Means to solve the problem]

Generally, piping support mechanisms have mechanical play, so
The heat transfer in actual piping is microscopically nonlinear. In the case of a mechanical snubber, the surface pressure acting on the ball screw is not constant; when the pressure reaches a certain value, it is released by the movement of the stroke of the mechanical snubber, and this repetition allows thermal displacement of the piping. During the stroke movement, mechanical vibrations are generated in the mechanical snubber and the piping support system connected thereto. The present invention focuses on this vibration and detects this vibration to achieve the above object. That is, the present invention is an in-service inspection system equipped with a detector for determining the soundness of a mechanical snubber, which is an earthquake-resistant piping support device, and the detector detects the mechanical damage that occurs during stroke movement of the mechanical snubber. This is an accelerometer that measures mechanical vibrations of the snubber and the piping support system connected thereto, and the accelerometer can be mounted on or near the body of the mechanical snubber.

[For use]

When the output of the plant is increased or decreased, if the mechanical snubber is functioning properly, the stroke of the mechanical snubber will shift due to the thermal displacement of the piping.
The mechanical vibrations of the mechanical snubber and the pipe support system connected thereto are measured by an accelerometer. However, the mechanical snubber was not functioning properly,
If the thermal displacement of the piping is restrained, the mechanical vibration will not be measured because the stroke of the mechanical snubber will not move. In addition, if the restraint of thermal displacement of piping caused by a mechanical snubber failure is suddenly released due to some stimulus throughout the period from the start of plant operation to the end of operation, excessive vibrations will be measured by accelerometers. . Therefore, it is possible to make an appropriate judgment regarding the soundness of the mechanical snubber from the results of vibration measurement using the accelerometer.

【Example】

The present invention will be described below with reference to embodiments shown in the drawings. In FIG. 1, A is inside the reactor containment vessel, and B is outside the reactor containment vessel. A mechanical snubber 3 is installed between a fixed wall 2 and, for example, a sodium-based pipe 1 provided in a reactor containment vessel A to which workers cannot enter. Since the function and structure of the mechanical snubber 3 are as described above, their explanation will be omitted. As mentioned above, the mechanical snubber 3 is a ball screw 4.
When the surface pressure acting on the snubber reaches a certain value and the ball nut 5 moves as the ball screw 4 rotates, mechanical vibration is generated in the mechanical snubber and the piping support system connected thereto. A mechanical snubber is used to detect this mechanical vibration.
On the body of 3 or in its vicinity within the vibration propagation range, a small accelerometer 7 is mounted by screws or adhesive. The accelerometer 7 may be a commercially available accelerometer. FIG. 3 schematically shows the internal structure of a typical accelerometer 7. 8 is a weight, and 9 is a piezoelectric element. Take accelerometer 7;
There is no need for any adjustments such as positioning to set the position. The charges generated by the accelerometer 7 are led to the outside of the reactor containment vessel B through a signal cable 10, which is accessible to workers, and then connected to a charge amplifier 11 and a data acquisition device 12. The testing method is as follows. If the accelerometer 7 detects mechanical vibrations occurring during stroke movement of the mechanical snubber 3 when the output of the plant increases or decreases due to thermal displacement of the piping 1,
The function of the mechanical snubber is judged to be sound. On the other hand, if no vibration is detected, this can be said to be a result of the thermal displacement of the piping being restricted, and it is therefore determined that the mechanical snubber is not functioning properly. In addition, if excessive vibration is measured by the accelerometer from the start of plant operation to the end of operation, it can be said that the restraint of thermal displacement of the piping has been suddenly released due to some stimulus. It is determined that the functionality of the equipment was unhealthy.

【Effect of the invention】

As explained above, the present invention uses a small accelerometer to detect the mechanical vibrations of the mechanical snubber and the piping support system connected thereto that occur during the movement of the mechanical snubber's stroke. This made it possible for the first time to conduct inspections during the service period. In principle, accelerometers have a structure that does not cause mechanical failure, and they can be simply fixed with screws or adhesives on or near seismic piping support equipment, which would otherwise require special adjustments. . Moreover, since there is no fluctuation in the indicated value due to drift and there is a margin in detection sensitivity, it is not affected by a slight deterioration in the sensitivity of the acceleration pickup, so it is excellent in that highly reliable detection is always possible. = 9- Note that when a radiation-resistant accelerometer is used, the frequency of maintenance can be significantly reduced, and the exposure dose equivalent of the workers involved can be reduced.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the in-service inspection system for the seismic piping support device according to the present invention, Fig. 2 is a partially cutaway perspective view schematically showing the internal structure of the mechanical snubber, and Fig. 3 is an accelerometer. 4 is a diagram for explaining a conventional inspection method, and FIG. 5 is a sectional view of the displacement detector shown in FIG. 4. 1... Piping, 2... Fixed wall, 3... Mechanical snubber 14... Ball screw, 5... Ball nut, 6... Flywheel, 7... Acceleration 31.8... Weight,
9...Piezoelectric element, 10...Signal cable, 11...
- Charge amplifier, 12... data acquisition device.

Claims (1)

[Claims] 1. An in-service inspection system equipped with a detector to determine the soundness of a mechanical snubber, which is an earthquake-resistant piping support device. An in-service inspection system for an earthquake-resistant piping support device, which is an accelerometer that measures mechanical vibrations of a piping support system that causes vibrations, and is characterized in that the accelerometer is installed on or near the main body of a mechanical snubber.