INITIATION AND EARLY GROWTH OF CREEP CRACKS FROM PREEXISTING DEFECTS

Concepts relating to the initiation and early growth of creep cracks from pre-existing defects are reviewed and illustrated with original data for 1CrMoV steels. Creep crack initiation (CCl) occurs on the attainment of a critical local crack-tip strain, the magnitude of this strain depending upon the creep ductility of the material and the crack initiation criterion selected. A weakness with the existing CCl database is that the information has not been accumulated in a consistent manner and the adoption of a unified methodology is encouraged. An understanding of the process of CCl and early growth has been developed by specialists from Europe, the USA and Japan to a level where high-temperature defect assessment can now be performed with some confidence. However, there is still a need for more effort to improve the extent of knowledge and the effectiveness of the methods employed to collect and apply experimental data to engineering structures.