Maintenance Methods And Applications For Shallow Water Aged Oil Platforms

The dissertation focuses on maintenance methods and its applications for shallow water aged oil platform, which is a part of the"863"High Technology Research and Development Program of China (No.2006AA09Z355).The study is based on fundamental theory of offshore platform repairing and the key technology in china and abroad. Maintenance methods and applications for shallow water oil platform is investigated systemically based on theoretical research, numerical calculation and computer simulation, and much progress is achieved including improving of maintenance equipments and technology of aged offshore platform, scour mechanism of shallow water platform pile and its preventions, new material used in platforms repairing, classificatiaon of platform mainterance, optimization and its maintenance strategy, disposal and utilization of aged offshore platform, and so on.The main works are summarized as follows:1 Techniques and Processes of Strengthening, Modification and Repair for Aged Offshore PlatformThere are some factors to shorten the service life of offshore platform, which can be summarized as these categories: fatigue loads; dropped objects; vessel collision; corrosion; damage during installation; welding and/or fabrication fault; explosions; ice; build-up of drill cuttings; under-design. The factors and their results lead to a requirement for strengthening, modification and repair as follows: remove damage; dry welding; wet welding; grout filling; weld improvement; composites and so on. A comparative study on advantages and disadvantages of present repair methods were put in practice with the engineering practice of ShengLi shallow water oil field. A simple steel habitat is designed. The installation and construction of the habitat is convenient. Theory analysis and ANSYS finite element calculation show that the habitat is not restricted to depth of water. Clamping technology is studied and the design process for clamps is obtained.2 Scour Prevention Methods for Offshore Platform of Shallow Water Oil FieldScour can result in removal of vertical and lateral support for foundations, causing undesirable settlements of pile foundations and overstressing of foundation elements. It not only can increase loads on platform, but also can cause production line of jacket platform easily to fracture. It is difficult to change the external environment conditions(such as wave, current and periods) to prevent scour. Prevention methods of fluid diversion and self-bury are designed. Methods of these two scour prevention are simulated by Fluent to find out how can the parameters affect the purpose of prevention. The devices are optimized by the simulated results. The factors of sands and silts' movement are considered. And the experiment of orthogonal method is used in simulation design and analysis. Results obtained from the computer models have demonstrated that the combination of CFD simulation and orthogonal design is suitable for the scour prevention. The idea of changing local flow field around the pile is an economic practicable method.3 Carbon Fiber Used in Maintenance of Aged Jacket PlatformTo improve the quality and economy of strengthening, modification and repair techniques of aged offshore platform, developing the present processes and introducing a new material called Carbon Fiber Reinforced Polymer(CFRP) are prefered. Mechanical properties of carbon fiber are studied theoretically and strengthening processes with unidirectional carbon fiber sheets are discussed. A new method of its application in strengthening platform components is brought forward. Strengthening used prestressed carbon fiber sheets are analysed with crack stress intensity factors. And some interesting results are obtained.4 Maintenance Strategy, Management and Maintenance Program Optimization of Offshore Platform and Prolong Aged Offshore Platform's LifeOffshore platform maintenance means keeping or restoring the platform in the required state. The cost can be controlled by carrying out maintenance in premeditated plane and effective decision making of repair contents and repair cycle. Considering certain technical factors and economic factors, style and degree of repair are prescribed. Classification of offshore platform maintenance is made based on the Level of Repair Analysis(LORA). Level of Repair Analysis(LORA), Reliability Analysis(RA) and Maintainability Analysis(MA) are beneficial to implementation of repair. And it can give some advices to design and construction of a new platform to increase availability. The whole failure probability can be obtained by systemic connection in series or parallel and their calculation. Maintenance sequence of faulty components can be gained through comparison between their critical importance. And further maintenance optimization can be done with the results. The platform reliability along with the time variation can be obtained through the anlysis of failure ratio and repair rate with Markov analysis.The effective use of aged platforms are not only meet the standard of the environmental but also save the cost of oil production. An example calculation of aged platform for wind power generation is given. The method of reconstruct for other use have some practical value for real processing and guiding significance for offshore platform disposal.