Abstract:

It is easy to form oxide scale on the surface of the stainless steel used in supercritical utility boiler tube under the action of high-temperature and high-pressure steam. As the flake of the scale may jam the boiler tube and lead to overtemperature tube burst,it is necessary to detect the scale and take some measures in advance. In this paper,several detection methods of oxide scale were compared and the magnetic-field measurement accuracy
was experimentally investigated under the conditions of different clearances between the probe and the tube,different deflection angles between the probe and the tube diameter and different relative positions of the permanent magnet and the scale. It is indicated that ( 1) when the clearance,the deflection angle and the relative position are respectively less than 1.07mm,within 25.9° and less than 26.4°,the measurement error can be controlled within 5%; ( 2 ) the clearance between the probe and the tube is the main factor that affects the measurement; and ( 3) the measured magnetic field intensity exponentially increases with the deflection angle and the relative position.

Key words: boiler tube, oxide scale, nondestructive testing, magnetic field intensity, measurement accuracy