Certification of Fixed Steel Platforms in the North Sea

Abstract

ABSTRACT The paper deals with the certification process of a large fixed steel platform in the North Sea with particular emphasis on the analytical systems developed within the Ocean Engineering Department of Lloyd's Register of Shipping, to provide an effective independent design appraisal. The trend away from generalised rules towards the standardization of acceptable methods of design and construction is covered with examples of the results of some of the. 50 platforms already analysed. The critical conditions analysed, the loading for static and fatigue, and the computation of margins of safety are described. GOVERNMENT REGULATIONS UNITED KINGDOM NORTH SEA Installations, fixed or mobile, used in the exploration and exploitation of mineral wealth in U.K. waters must satisfy the Offshore Installations (Construction and Survey) Regulations 1974, under Section 3 of the Mineral Workings (Offshore Installations) Oct. 1971. These stipulate the relevant technical requirements and specify that each offshore installation must possess a certificate issued by a Certifying Authority stating that it is fit for use in U.K. waters. The 'Certificate of Fitness' will be based on an independent assessment of the design, method of construction and operations manual and on associated surveys carried out by surveyors appointed by the Certifying Authority. The basis on which a certificate is issued, is outlined in the 'Guidance on the Design and Construction of Offshore Installations' (Department of Energy). To this date, five Certifying Authorities have been appointed, of which Lloyd's Register of Shipping is one. Since it has always been the Society's policy that classification of a fixed platform would be based not only on the submitted calculations/plans etc. but also on its own independent assessment of the design and survey during construction, there were only minor extensions in procedure required to encompass the full certification process. The Society's worldwide network of exclusive surveyors ideally suited the international nature of all offshore construction. Although this paper is primarily concerned with the structural design assessment, a. summary of the Society's total involvement in the certification process is presented in Appendix A and guidelines on the information required to be submitted for certification is given in Appendix B. STRUCTURAL DESIGN ASSESSMENT The complexity of fixed steel platforms caused by their particular operational specifications and their design dependence on local environmental factors, soil conditions, method of launching and installation has led, in the North Sea, to the situation where each configuration is unique. This uniqueness in turn, has caused rigid rules to give way to generalized acceptable standards of load criteria, methods of analyses and construction and fabrication requirements supported by an independent assessment. The system 'LOPS' (Fig. 1) developed within the Society for the analysis of fixed steel platforms will have been used by the end of the year on the assessment of over 100 steel platforms. Though the majority have been in the North Sea, platforms located Offshore Congo, Tunisia, New Zealand Middle East and Indonesia have already been checked using this system.