Inspection Reliability for Offshore Structures

The assessment of fatigue cracks in offshore structures involves stress analysis, fatigue fracture mechanics analysis and knowledge of the likely loading on the damaged member. Before embarking on the analysis it is necessary to assess the input information on the presence, location and size of any defect. This requires detailed information on the reliability of the nondestructive testing technique used for the inspection. Inspection reliability data is also extremely important for inspection scheduling especially in situations where reliability based inspection scheduling is to be used. To produce this type of data is expensive and time consuming as it involves blind trials, and a large sample containing realistic defects. The ICON project [1], a major EU Industry funded project, addressed this problem and conducted inspection reliability trials for the offshore industry. ICON and the subsequent ICON User Group produced a large database on fatigue crack detection and sizing techniques. This data is now available in the ICON User group Software. The paper has used this software to produce POD data for ACFM and MPI. The POD data has been assessed in terms of crack categories (including categorisation based on BS7910), the influence of spurious indications, and in terms of the influence it has on fatigue crack growth predictions.