A fracture mechanics interpretation of the DNV brittle fracture criteria for ships and mobile offshore units

Design procedures against brittle fracture are either based on empirical experience based methods or theoretical fracture mechanics based methods. Frequently, the fracture mechanics based assessment procedures are suspected to be tools by which to get acceptance for poor quality. In reality, these suspicions are somewhat unfounded, since the manufacturing standards, implicitly, also assume some specific defect size.
The standards contain specific inspection criteria, which in themselves lead to some specific possible accepted defect size. The problem has been that the manufacturing standards have not been evaluated based on an advanced fracture mechanics analysis. Here the Det Norske Veritas (DNV) rules for ships and mobile offshore units are analysed, applying the state‐of‐the‐art fracture mechanics assessment method SINTAP. Based on the assessment, the consistency of the DNV rules, with respect to strength level and inspection criteria is revealed. The assessment, also creates the possibility to extend the rules to thinner and higher strength steels.