Toshihiko Yamaguchi

A method for detecting bearing wear in a drain pump utilizing an eddy-current displacement sensor

Abstract A simple method for directly measuring bearing wear has been developed by means of an eddy-current displacement sensor. The system consists of a sensor head unit, including a displacement sensor and aluminum functioning foil as a target metal, a data processing system including an amplifier, an A/D converter of 14 bits, a personal computer, and a display. The error of this system was approximately 2 μm, which is sufficient for practical use. Another error caused by the system when used in a plant is discussed theoretically, and a method for the correct estimation of bearing wear without this error based on smoothing, i.e., an averaging of the sampling data, is proposed.

An optical system for monitoring torsion in a power transmission shaft in realtime

An optical system has been proposed and verified experimentally for monitoring the torsion of a power transmission shaft in realtime. The system consists of a pair of lasers, mirrors and light receivers as a sensor head, and logic circuit, high-frequency oscillator, and computer as a data processing system. The smallest measurable angle of torsion can be expressed by co/f, where co is the rotational frequency of the power transmission shaft andfis the frequency of the oscillator. The experimental error was found to be a few percentage points.

3D RF‐ECT SIMULATIONS OF ISI OF U‐BEND SG TUBES IN FBR

The paper focus on 3‐dimensional finite element simulations of the steam generator inspection using remote field eddy current testing (RF‐ECT) in order to asses the performance of the in‐service inspection in SG tubes. It is evaluated the influences of the SG tubes U‐bend curvature on the eddy current sensor signal by taking into account a 3D model in which also multiple SG tubes are located close to each other, as in the nuclear reactor.

Inspection of the Steam Generator Heat Transfer Tubes for FBR Monju Restart

Japanese prototype FBR Monju will restart its operation for the first time since the occurrence of the sodium leak accident in 1995. The integrity of its components after the long suspension needs to be confirmed before restarting. One of the most important components of Monju is steam generator (SG) unit that was first tested in the 2007.11–2008.3 period during plant-confirmation test. The safety authority required that Monju components should have as same integrity as at the beginning of the first operation in 1994. Now the SG tubes have been installed in the vessel and it is impossible to test them directly. In order to satisfy the safety authority requirement, presumable deteriorations of SG tubes in the long-term suspension were investigated at first and these were limited to only the lack of thickness by corrosion, which are detectable by three tests: eddy current testing (ECT), visual testing (VT), and leak check. These tests were performed with customized procedures and evaluated for appropriate criteria. The ECT was applied to check for the lack of thickness of SG tubes caused by regional corrosions. The ECT probe passes through the full length of a tube with the speed of 200mm/s. Integrity of the tube was checked by amplitude and phase chart. Threshold of the approval thickness was decided based on the tube data at the time of manufacturing. The thickness of the tube is 3.5mm and it cannot be reduced less than 7% lack of the thickness. The characteristic signal at special points like bends or SG support plates were identified by their phase chart. Based on these evaluations, no significant deterioration was detected in SG tubes excepting the special undetectable region. The VT checked for corrosions on the inner surface of tubes. It covers the undetectable regions by ECT. The testing region is between the tube-plate and the bottom U tube along the down comer. The condition of the other regions, subjected to the same environment conditions (temperature, humidity, time not being in service, others) is expected to be similar to the tested region. A customized CCD camera was operated with about 10 mm/s along the tube. The test did not reveal any significant corrosion. The leak test checked for penetrating holes in SG tubes. After keeping a high pressure argon gas outside of SG tube, the nitrogen gas inside of SG was pumped to a mass spectrometer. In this test, no argon gas was detected by the mass spectrometer. After evaluation of all results of three tests, it was confirmed that there is no significant lack of thickness and penetrating holes in SG tubes. Therefore, it was proved that SG heat transfer tubes have the required integrity for reoperation.© 2009 ASME

Experimental Measurements of Eddy Current Signal From SG Tubes of Fast Breeder Reactor Covered by a Thin Sodium Layer Using a SG Mock-Up

In Fast Breeder Reactors (FBR) which are sodium cooled, the steam generator (SG) heat exchanger tubes separate the low pressure sodium flowing in the SG vessel with the high pressure water-steam in tubes. During In-Service Inspection (ISI), sodium is first drained and then SG tubes are cooled down to the room temperature. After sodium draining, due to the high temperature (more than 500 °C), sodium adheres to SG tubes and structures around (SG support plates, welds) in a thin layer, filling eventually the gaps between SG support plates and tubes. During ISI, SG tubes are inspected for cracks and corrosions using differential eddy currents (EC) probes. Due to the high electrical conductivity of sodium adhering to the outer SG tube surface, the eddy current testing (ECT) signal modifies, in accord with sodium layer thickness or sodium deposits located on the outer SG tube surface. The sodium wetting properties depends on several factors as: material surface, temperature and sodium wetting time. The effect of sodium adhering to the outer SG tube on ECT signals were measured using a small mock-up tank (2 m high and 0.7 m in diameter) in which were introduced two SG tubes similar with the ones used in the Monju FBR (one tube is ferromagnetic and made of 2.25Cr–1Mo alloy, while the other one is made of SUS321 and is austenitic). Defects, SG support plates (on both helical and straight part of the tube) and welds were added to tubes and the ECT signal was measured before and after sodium draining. Variations in the sodium layer thickness and consequently its effect on ECT signals were measured by filling and draining the tank three times in order to recreate each time new layers of sodium. The paper describes the experimental conditions and the ECT results for both types of SG tubes by comparing the defects, SG support plates and weld signals before and after draining of sodium. Additionally, sodium structures were examined visually using a VideoScope camera, confirming the recorded ECT signals. The paper also presents details about sodium layer thickness measurements in several parts of SG tubes (near defect, SP, weld, bend, helical tube, straight tube) by scratching and collecting the sodium on a small area of 20mm×20mm. The volume of sodium drops is also estimated. The measurement results showed that there are significant differences in the sodium layer thickness depending on the SG tube material.© 2009 ASME

EDDY CURRENT SIMULATIONS AND MEASUREMENTS OF SODIUM EFFECT FOR MAGNETIC AND NON‐MAGNETIC STEAM GENERATOR TUBES OF FBR

In fast breeder reactor (FBR), the steam generator (SG) tube wall is the only barrier between water steam and sodium flow. Eddy current signal (ECT) from outer tube defect is modified by both SG support plates (SP) as well as by sodium layer and unknown sodium drops located on the outer SG tube surface. In the present paper, ECT finite element simulations are conducted to evaluate sodium structures ECT noise and variations of defect and tube support plate signal in the presence of a thin layer covering the SG tube surface. Numerical simulations are validated and calibrated with experimental measurements of artificial outer defect for both magnetic and non‐magnetic SG tubes in the absence or presence of sodium covering the outer surface of SG tubes. The papers presents also details about measurements of sodium structures (drops, layer) formed on the outer SG tube surface when these are soaked in a test tank filled with sodium at high temperatures (500° C) up to two hours.

Development of a hybrid ECT sensor for JSFR SG double-wall tubes

ABSTRACT A new design has been adopted for the steam generator (SG) tubes of the Japan Sodium-cooled Fast Reactor (JSFR) using double-wall tubes. This paper estimates and assesses the effectiveness of detecting defects in SG double-wall tubes of the JSFR by using combined high-frequency eddy current testing (ECT) and low-frequency remote field eddy current sensors. We confirm that the proposed hybrid ECT sensor is highly sensitive to small defects, fatigue cracks, and other defects even when located under support plates of tubes. The parameters of the hybrid ECT sensor are designed and optimized to detect small defects using accurate numerical simulations based on the finite element method, using an in-house developed code. The sensitivity and high performance of the hybrid ECT sensor was validated with experimental measurements.

Pinhole detection system for glass wool paper by electric discharge

Abstract A pinhole detection system for glass wool paper has been developed based on electric discharge phenomenon. The main part of the system consists of two electrodes, i.e. anode and cathode, through which the glass wool paper passes. The line cathode consists of many needles with an equidistant separation of 6 mm. Three sets of line cathode, with needles at intervals of 6 mm, were shifted 2 mm from each other. A high resistance of 100 MΩ was used in the electric circuit to control the discharge current, i.e. damage to the paper. The detectable pinhole size using this system was between 0.1 and 1 mm. The detection rate was above 70%. The production rate of satisfactory goods was increased to approximately 33% as demonstrated in a manufacturing plant.

A simple optical method for measuring the vibration amplitude of a speaker

A simple optical method has been proposed for measuring the vibration amplitude of a speaker vibrating with a frequency of approximately 10 kHz. The method is based on a multiple reflection between a vibrating speaker plane and a mirror parallel to that speaker plane. The multiple reflection can magnify a dispersion of the laser beam caused by the vibration, and easily make a measurement of the amplitude. The measuring sensitivity ranges between sub-microns and 1 mm. A preliminary experiment verified the reliability of this method.