Measurement of Thinned Water-Cooled Wall in a Circulating Fluidized Bed Boiler Using Ultrasonic and Magnetic Methods

Abstract

In this paper, a nondestructive inspection system is proposed to detect and quantitatively evaluate the size of the near- and far-side damages on the tube, membrane, and weld of the water-cooled wall in the fluidized bed boiler. The shape and size of the surface damages can be evaluated from the magnetic flux density distribution measured by the magnetic sensor array on one side from the center of the magnetizer. The magnetic sensors were arrayed on a curved shape probe according to the tube’s cross-sectional shape, membrane, and weld. On the other hand, the couplant was doped to the water-cooled wall, and a thin film was formed thereon by polyethylene terephthalate. Then, the measured signal of the flexible ultrasonic probe was used to detect and evaluate the depth of the damages. The combination of the magnetic and ultrasonic methods helps to detect and evaluate both near and far-side damages. Near-side damages with a minimum depth of 0.3 mm were detected, and the depth from the surface of the far-side damage was evaluated with a standard deviation of 0.089 mm.

Special Issue: Novel Approaches for Nondestructive Testing and Evaluation

“…In this paper [9], a nondestructive inspection system was proposed to detect and quantitatively evaluate the size of the near-and far-side damages on the tube, membrane, and weld of the water-cooled wall in a fluidized bed boiler. The shape and size of the surface damages were evaluated from the magnetic flux density distribution measured by the magnetic sensor array on one side from the center of the magnetizer.…”

Theoretical Model of Self-Magnetic Flux Leakage and Its Application in Estimating the Depth Direction of a Fatigue Crack

“…Several studies have presented a theoretical equation for the leakage flux generated around a crack using a dipole model [22][23][24][25][26][27][28][29][30][31]. A formula was presented for the magnetization of a specimen by an external magnetic field, assuming that the magnetic dipole moment per unit area occurs at the crack surface.…”

“…A formula was presented for the magnetization of a specimen by an external magnetic field, assuming that the magnetic dipole moment per unit area occurs at the crack surface. The formula has been used as a model that simulates the qualitative (and partially quantitative) change in MFL based on the presence of defects [22][23][24][25][26][27] and sensor designs [28,29], and is used for quantitative evaluation [22][23][24][25][26][27][29][30][31]. However, it is difficult to apply it to very narrow cracks, such as fatigue cracks.…”