On the re-characterisation of defects in structural integrity assessments due to snap-through

TAGSI was asked by HSE/NII to comment on the effectiveness of the R6 procedure which permits a surface defect failing an initial assessment to be re-assessed as a through thickness defect of increased length. If the defect passes the re-assessment it may then be considered acceptable. In TAGSI's view re-characterisation needs to be considered separately for contained plastic collapse and ductile or brittle fracture of the remaining ligament. For plastic collapse and ductile tearing of the remaining ligament the R6 rules for re-characterisation appear generally satisfactory. For brittle failure of the ligament in many cases the R6 recommendations will be found satisfactory but for cases of large difference between static and dynamic toughness it is recommended that scoping calculations should be carried out for the defect geometry, loading and material properties of concern. © 2006 Elsevier Ltd. All rights reserved.