Methodology of Digital Image Acquisition and Digital Inspection for Liquid Penetrant and Magnetic Particle Testing

Abstract

Liquid Penetrant Test (PT) and Magnetic Particle Test (MT) are widely used in industry to detect surface defects. It is extremely important to maintain the repeatability and reproducibility of PT and MT so that they are able to detect any defect that might affect the quality of a product, especially the weld joints of welded structures. In the present paper, calibration methods for visual conditions for PT and MT are proposed with the use of a visual resolution gauge. In addition, a “PT/MT support System” applying digital image processing techniques, which enables us to perform “Remote Inspection” is proposed. A visual resolution gauge is a transparent plate on which line pairs are printed with equivalent hue to the indications of PT and MT, which ensures proper resolution for visual testing. In Japan, the standard for calibration methods for visual conditions using these resolution gauges for PT and MT were published in the Japanese Industrial Standards (JIS) Z 2340 in 2002. By applying these visual resolution gauges, we developed a “PT/MT support system.” In this system, the PT or MT digital images, which are captured by digital camera with resolution gauges, are converted into hue and saturation data by image processing. These images are then divided into two categories of defects and false indications. This is useful in detecting defects and establishing standard evaluation criteria. Furthermore, this will also enable “Remote Inspection,” which is a method in which PT and MT digital images are observed from remote place (as opposed to direct observations). This enables the possibility of inspections being performed from remote places and manufacturers, inspectors, customers, and government inspectors in remote areas can share the inspection results as electronic data.