Crack propagation characteristics in the nozzle corners of a pressure vessel steel model of light water reactor

The present paper describes experimental results which were obtained by measuring the propagation length from an artificial crack in the inner corner surface of the nozzles using an electrical resistance method and crack gage, when internal pressure was cyclically loaded to a steel model of reactor pressure vessels. In order to investigate the effects of the shape of nozzles and artificial cracks on the crack initiation life and propagation rate, in this experiment four different shapes of nozzles (each diameter ratio of nozzle to shell is 0.045, 0.075, 0.10 and 0.15) were attached to the pressure vessel model and two different types of artificial cracks (the shape of each crack tip is curved (A-type) and straight (B-type)) perpendicular to the direction of the maximum circumferential stresses were machined at the inner corner surface of each nozzle. From this experiment, it was apparent that the crack initiation life for the crack tip of a A-type was shorter than for that of B-type in every nozzle and for the crack initiation life at each inner surface of nozzle and shell there was not any distinct difference between A and B. The crack propagation rate from the crack tip was initially very large for all artificial cracks with number of cycles after crack initiation to reach a maximum value, it decreased also rapidly until each crack attained the surface tip of each artificial crack and increased with the crack length after that. After each crack passed the surface tip of each artificial crack, is propagated dependent on the diameter and thickness ratio of nozzle to shell, i.e., the crack propagation rate increased generally with increase of their ratios. The tendency was consistent with the magnitude of the circumferential stresses with increasing the diameter ratio of nozzle to shell at the vicinity of the inner corner surface of each nozzle