Study On Reliability Of Offshore Platform Structures Subjected To Accidental Disaster

The safety and reliability of offshore platform structures is one of the most important research areas on ocean engineering with difficulties and challenges. The exploration for oil and gas in ever increasing water depths has given an impetus to research efforts on the behavior of offshore structures subjected to accidental disaster. In this paper, based on the analysis and summarization of research present state and perspectives, special studies are placed on the large and complicated offshore jacket platform structures, which are introduced in the current trends of development and research. The research works include: risk assessment of platform structures subjected to accidental disaster, the collision mechanism between ship and offshore platform jacket structures, the deformation and energy absorption of platform jacket structures subjected to collision, explosion and fire load of jacket structures, platform structure reliability subjected to fire, structure response of platform subjected to explosion, system reliability of platform damaged structures, ultimate bearing capacity structural system reliability analysis, maintenance decision of platform jacket structures, repair and strengthening schemes assessment of the damaged members of jacket structures, release and protective system of platform structure subjected to accidental disaster. Applied research results to WEN 13-1 platform jacket structure and BZ28-1 south platform structure, significant economic effects are produced.The research results both are improved for reasonable design and scientific maintenance, assessment of safety for offshore platform during its service, but also provides reliable assurance for exploitation of oil and gas resources. The major contents are summarized as follows:(1) On the basis of risk assessment methods, risk assessment system of platform structures subjected to accidental disaster is established. The probability for occurring accidental disaster and the exposure level of the platform are considered as the gist to divide the risk level of disaster event. The risk assessment is developed on risk level. Structural reliability of platform subjected to collision, fire and explosion is studied to assure the integrality safety of platform structures subjected to accidental disasterrespectively.(2) An evaluation method for the damaged platform structure subjected to collision is established. On the base of the inspected results for some damaged members of WEN 13-1 offshore jacket platform being impacted by the large tonnage Derrick & Lay Barge during installation of steel jacket structures, numerical simulation is applied to analysis the collision process. It uses the manner from simple to complexity to simulate the impact load. A mechanics model is presented for the static and dynamic analysis of ship-platform collision system, and the static equivalent intensity analysis is applied to the damaged X diagonal brace member of platform structure. In the course of dynamic elastic-plastic analysis of offshore platforms, the added mass coefficients for the seawater dynamic effect and the structure-pile-soil mutual interaction are considered in the analysis of computational model. The nonlinear springs are introduced for the simulation of the force-deflection relationship of the local indentation for the damaged X diagonal brace. The curve of indentation deformation of the damaged member and different collision contact time is simulated under the velocity of ship being assumed. According to the curve, the formula of indentation deformation of the damaged member and different collision contact time is obtained to determine the maximum impact load. The damage extents of total platform jacket structures are also evaluated to choose feasible and reasonable repair and strengthening schemes of grouted clamping for the damaged members.(3) The energy absorption and transformation of collision between ship and platform structure is studied to establish the energy absorption model of collision. Based on the energy absorption theory, the wall thickness of brace member and pile leg is designed. While the diameter of brace member is bigger, the design value of wall thickness is smaller. While the diameter of pile leg is smaller, D/t value is bigger, and then the reduced ultimate bearing capacity value of damaged member after collision is bigger.(4) The elastic-plastic analysis method is adopted to analyze the finite element calculation model of BZ28-1 south platform structure, The standard temperature-time curve is adopted to establish the temperature calculation model of fire. Based on energy conservation theory, the heat of conduction, radiation and convection on the platform structure is analyzed, the temperature field of members subjected to fire is calculated. The relationship between platform structure temperature and time is...