Implications of Cleavage Fracture Criteria for Structural Integrity Assessment of RPV Steels

To accurately assess the safe operation of structures containing defects, it is necessary to consider the influences of previous load cycles on crack propagation. A number of current assessment codes contain advice to account for strain history and residual stress, but are generally known to be highly conservative which may potentially result in the unnecessary and expensive repair or replacement of infrastructure. This paper considers the results of previous investigations into cleavage fracture of an A533b RPV steel to determine the accuracy of the widely used R6 structural integrity assessment procedure for fracture following significant load history. The levels of conservatism associated with a number of assessment methods are discussed and compared with experimental data. The general trends suggested an improvement in assessment accuracy may be obtained by using local approach methods, compared to crack tip failure parameters. It is noted however that all the methods used produced some unsafe estimates of failure load, which is felt to be related to an over estimate of the characteristic material toughness.