Crack tip opening displacement (CTOD) methods for fracture assessments: Proposals for revisions to BSI PD 6493

TWI Industrial Member Report Summary 371/1988

By S J Garwood, J R Gordon, A A Willoughby, R H Leggatt and T Jutla

Background

The British Standards Institution document PD 6493: 1980 'Guidance on some methods for the derivation of acceptance levels for defects in fusion welded joints' is currently under revision. The new document will build on the many advances in fracture mechanics technology over recent years, to provide a more versatile and accurate framework for defect assessment. It is proposed in this report that the fracture sections of the revised document will take the form of two separate assessment routes, dependent on the fracture toughness data available, i,e. either K or CTOD, and will allow three levels of assessment. In Part 1 of the report, the philosophy behind the three treatments and their interrelation is explained. Consideration of the fracture toughness data for input to the assessment, the treatment of primary and secondary stresses, the use of failure assessment diagrams for the assessment of known defects, and the prediction of limiting defect sizes are also covered.

In Part 2 five worked examples are presented demonstrating the proposed revision to the CTOD methods of PD 6493.