전열관 비파괴검사를 위한 실린더형 자기카메라 개발

Abstract

The initiation and propagation of degradation, corrosion, and fatigue can directly damage megastructures such as nuclear/thermal power plants, aging aircraft, petrochemical structures, manned space stations, and rocket engines, as well as microstructures such as IC (Integrated Circuit) packages and VLSI (Very Large Scale Integration) chips. This can endanger human life and cause additional economic losses, environmental pollution, and a decrease in national status. If such damage is discovered early and steps are taken to repair or replace the damaged parts, the systems can be used safely until the end of the designed life cycle. In addition, life cycles can be extended by studying damage tolerance. Damage initiation and propagation are classified as that occurring (1) in the manufacturing stage or (2) operating stage. The damage could be detected in a pre-service inspection (PSI) or in-service inspection (ISI), respectively, followed by recovery. Nondestructive testing and evaluation (NDT&E), which investigates the existence, location, size, shape, and distribution of damage during the PSI and ISI, requires new technologies with higher speeds and smaller crack detection without needing to clean the specimen or make contact. NDT&E also requires a quantitative evaluation algorithm and database. Additionally, the ability to detect smaller cracks results in (1) inspection results with high reliability, (2) the detection of unexpected small damage, and (3) economic benefits resulting from the long time between inspections (reduction of fees, workers, and outage time during frequent periodic inspections). Although eddy current testing (ECT) is used to evaluate the safety of megastructures such as nuclear and thermal power plants, aircraft, spacecraft, steel-manufactured items, automobiles, and ships, ECT has some disadvantages such as signal analysis difficulty and difficulty differentiating between cracks and volumetric flaws. In particular, a heat exchanger tube (HET) in a nuclear power plant consists of a paramagnetic or ferromagnetic material, or a mixture of the two, with constitutional changes. Thus, it is difficult to evaluate with ECT. In addition, ECT could misread a local magnetization area as a flaw, or attribute a large crack to local magnetization. Therefore, there is a need for imaging technology to obtain the leakage flux or eddy current distribution inside the HET. In this research, a cylinder-type magnetic camera and two small-bore pipe specimens were manufactured. One of these specimens was made of a copper alloy (Cu 90%, Ni 10%) and the other was composed of austenite stainless steel (STS 304). Both specimens contained artificial flaws that were tested using the magnetic camera. The cylinder-type magnetic camera had a 32 × 32 Hall sensor array, high-pass filter (HPF) with a 284 Hz cutoff frequency, differential amplifier (60 dB), root-mean-square circuit, remotely controlled DC/AC power supply, switching circuit, and USB-type National Instruments data acquisition system (NI-DAQ). The eddy current distribution in a small-bore pipe was imaged using customized software. It also contained an automatic flaw detection and position detection system, and quantitative evaluation was possible using the software.