New Developments in Flooded Member Detection

Abstract

The improvement in our understanding of the fatigue lives of offshore welded tabular structures has led to a change in our inspection philosophy. For the older platforms we are able to predict very accurately where and when trouble can be expected. The newer structures have been designed to ensure that all nodal welds have fatigue lives in excess of three times that of the required working life of the platform, so there are no particular areas of concern. Any propagating defects in the new platforms will be due to fabrication faults which evaded detection during construction. Because the locations of these faults cannot be predicted, it is not possible to direct inspection programmes at any specific areas of high risk. Therefore a rapid method is required for checking primary members in the newer and older platforms for propagating defects. ROVs can check for gross damage, but it is desirable to detect defects as early as possible. The philosophy behind flooded member detection is that because all jacket members are seal welded in air at one atmosphere during construction, water within a member must indicate a through-thickness defect. The challenge has been to find an accurate, rapid and cheap method of checking jacket members for flooding and it has proved remarkably difficult.