SUPERSONIC FLAW DETECTING METHOD FOR CENTRIFUGAL CAST STAINLESS STEEL PIPE EXPOSED TO HIGH TEMPERATURE

摘要

PURPOSE:To enable to ascertain the state of deterioration correctly by fixing probes to different holders respectively and making transmitting pulses pass a part about 2/3 of the thickness of an inspected pipe from its outer surface. CONSTITUTION:Generally the crystal grains of a centrifugal cast stainless steel pipe 1 are coarse having highly directional property and the scattering and attenuation of supersonic waves in the pipe are serious, therefore, longitudinal supersonic waves of a frequency of 0.5-2MHz are used for flaw detection. Such supersonic waves are transmitted from a transmitting probe 3 electrically connected with a flaw detector 10 to the inspected pipe 1, received and converted into electric signals by a receiving probe 4 and outputted to the flaw detector 10. The existence and sizes of inside cracks 2 obtained by the flaw detector 10 are displayed as a chart 12 by a recorder 11. As the inside cracks 2 occur mostly in a part about 2/3 of the thickness of the inspected pipe 1 from its outer surface, the angle of incidence of the supersonic waves is set so that supersonic transmitting pulses may pass through said layer.