Magnetic images of surface crack on heated specimen using an area-type magnetic camera with high spatial resolution

Abstract

A micro-array method using Hall sensors was proposed in previous research by the authors. That array method allowed a two-dimensional magnetic field measurement with high spatial resolution using simplified connections. A wide range of magnetic fields could be measured quantitatively with high spatial resolution. This paper proposes a nondestructive testing (NDT) method using a magnetic camera with the previous micro-array method to detect cracks in a specimen at high temperatures. Distilled water has a boiling point of 373.15 K at atmospheric pressure. Therefore, the Hall sensor array, which is submerged in the distilled water, can be protected from an external high temperature of several hundred degrees Kelvin until the container is broken. If the Hall voltage of each Hall sensor changes according to the external magnetic field at the boiling point of the liquid, we propose that the crack can be detected in a high temperature environment using a magnetic camera submerged in the liquid. Plate specimens made of SS41 stainless steel, with slits in the each specimen, were used to verify the proposed NDT method using a high spatial magnetic camera in a high temperature environment.