Comparison of creep crack initiation and growth in four steels tested

In power generation plants and the chemical industries there is a need to assess the significance of defects which may exist in high temperature equipment operating in the creep range. For the life prediction methodology for cracked components developed under the HIDA (High Temperature Defect Assessment) Brite/Euram project, it is necessary to have a verifiable data-base of crack initiation and growth data in order to obtain relevant material properties for use in calculations. This paper examines the methods of analysis used. Four types of steels were tested in the programme. These were P22, 1CMV, 316LN and P91 in the parent, as welded and overaged conditions. The data have been obtained from seven participating laboratories. All the results were analysed in the same way using a programme called ‘ZRATE ’ developed to follow the ASTM E1457-98 testing standard. The results are compared with other crack initiation and creep crack growth data in the literature and with predictions produced from creep data using a model of the cracking process. It has been found that in all cases the scatter in the data is less than for the generic data in the literature. It has also been found that creep crack initiation and growth data can be correlated most satisfactorily in terms of the creep fracture mechanics parameter C*