A crack-driving force approach investigation of surface flaw interaction on tension-loaded pressure vessel plate

The problem of multiple crack-like flaws near one another, which might occur on pipeline systems and pressure vessels, is a complex phenomenon and has been dealt on industrial routines through methodologies contained on fitness-for-service (FFS) standards in a conservative manner by recharacterizing the flaws on a so-called bounding flaw. With this conservatism, the rational engineering-based assessment principle of these standards has been losing its meaning when evaluating on-going structural damage for maximization of operational life. On this article, a tension-loaded plate with surface flaws under interaction regime has been analyzed and the depth and aspect ratio, as well as the coplanar distance between the flaws have been varied to assess their influence on the interaction. It was observed that the decrease of the depth ratio induces a higher amplification of the crack-driving force regardless the elastic or elastic plastic interaction case. The criterion of 10% of amplification on the crack-driving force used on BS 7910 and API 579/ASME FFS-1 standards to start considering an interaction regime between flaws has only been observed for depth ratios higher than 0.70 and for lower values the amplification observed was much higher. The influence of the elastic and elastic plastic regime was also assessed and the elastic plastic interaction case is more critical as the depth ratio increases. As for the interaction criterion found on BS 7910 and API 579/ASME FFS-1, it is non conservative for the elastic interaction case and conservative for the elastic plastic interaction case. Nonetheless careful consideration should be taken as the latter should not only be characterized by the flaw dimensions, as the remote loading and work-hardening capacity of the material might have influence on this criterion.