Background to and validation of CEGB report R/H/R6—Revision 3

Abstract

This paper is a companion document to the third revision of the CEGB procedures for the ‘Assessment of the Integrity of Structures Containing Defects’, R6, and provides background information and validation. The background information includes details of the derivation, demonstrating the strong theoretical foundation of the procedures. Validation is addressed by comparison with tests on simple specimen geometries and structural components. This is supported and extended by comparing the procedures with the results of finite-element analyses. The most convincing validation is obtained by the direct application of the procedures to experiments on complex structures. Structural tests are, however, time-consuming and expensive to perform and so this class of validation is necessarily limited. The results on such components demonstrate the conservative nature of the R6 procedures with all failure points falling outside the failure assessment diagram. Contributions to the overall conservatism come from the failure assessment diagram and the procedures themselves, as well as from the calculational inputs and material properties used in individual assessments. The validation on structures is supplemented by comparing R6 assessments with experiments and finite-element analyses on test specimen geometries. As the calculational inputs and material properties are well defined for test specimens, this type of validation primarily addresses conservatisms in the failure assessment diagrams themselves. Results are presented for a range of specimen types, crack depths, specimen sizes and structural steels, and demonstrate the applicability of the Option 1, Option 2 and Appendix 8 failure assessment curves in R6. Finite-element solutions are described which extend the range of the validation by considering geometries with thermal stresses and geometries with shear loadings. Particular emphasis is given to thermal stresses because of the limited structural validation and an extensive series of finite-element solutions has been obtained within the CEGB. The results show that the R6 procedures adequately cover interactions between thermal and mechanical stress systems, although they are overly conservative at high thermal stresses. Similarly, the results for shear loadings show that the empirical approach adopted in Appendix 7 of R6 is reasonable. It is concluded that the procedures presented in the third revision of R6 are valid. The use of moderately pessimistic input data in assessments will ensure that failures are avoided.