A New Approach for Effective Underwater Hull Inspection of Floating Offshore Assets

Abstract

New hull inspection strategies and methods for reducing costs and increasing operational efficiency for floating offshore assets. (ODIN® Patents pending, see; www.emialliance.com/ip-patents) This paper describes the need for improved hull inspection strategies and methods for floating oil, gas and drilling assets and how these requirements are systematically being met by effective cooperation between regulators, operators and service providers. Floating production and mobile drilling units of all types require good hull integrity if they are to remain safe and efficient through their working lives. Good hull integrity requires meaningful and accurate data on hull condition and this comes from high quality inspection. Regulators require operators to assure the integrity of their hulls and this in turn requires inspection of the hull internal structure, isolation valves, sea chests and associated marine piping, external appendages and station keeping systems. Conventional methods of hull inspection, for example periodic drydocking, using divers, ROVs or rope access technicians, incur penalties of cost, safety, budgetary risk and significant additional personnel. The value of the data produced is also restricted by difficulties such as marine growth, limited access to isolation valves and so forth. The HITS (Hull Inspection Techniques and Strategy) JIP called for new methods to be developed that minimises diving operations, confined space entry and reducing residue removal prior to tank inspection. The initial focus was in improving the methodology for Underwater Hull Inspection In - Lieu of Drydocking (UWILD) and this paper focuses on how close cooperation between, operators, class societies, regulators and service providers brought about radical improvements in a short space of time. Key technical features of the new ‘diverless UWILD'strategy for underwater inspections include carrying out inspections from inside the hull, using advanced CCTV methods to inspect critical isolation valves and inspection of the hull appendages using ‘maintenance and observation’ class, mini-ROVs. An important change in the existing periodic survey strategy for underwater inspections was also required. Agreement on a new ‘continuous’ survey approach allowed the use of ‘Long Term Inspection Plans’ that aligned the ‘underwater’ inspection scope with planned tank entry for the Continuous Hull Survey programmes. This provided better information, reduced and spread costs and provided planned scopes which helped avoid budget over-runs. Practical application of the approach has demonstrated cost reduction of greater than 20% with over 70% reductions in POB (Persons On Board) coupled with minimal downtime and improved data quality. Further advances in hull inspection are currently being developed to eliminate man-entry to confined spaces, such as tanks, and the inspection of cargo tanks with reduced cleaning effort. This paper describes how these rapid advances have been made on the inspection challenges identified by the HITS JIP and the close cooperation between Operators (SBM), Classification Societies (ABS) and Service Providers (EM&I).