Ultimate Strength Analysis Of A Jacket Platform

As the large-scale basic facility for ocean petroleum resource development, the offshore platform is the base of production and living on the sea. In recent years, many offshore platforms in our country reach their lifetime limitation, and its safety assessment should be discussed urgently. Continuous studies are made by both domestic and overseas scholars in ocean petroleum enterprises. Thus, the theory of safety assessment has been developed and improved, which will offer the service and guarantee for our ocean business. The ultimate strength analysis of offshore jacket platform is an important part of the whole safety assessment of existing platforms. With the rapid development of offshore oil industry, the departments of design and inspection, maintenance and repair in the offshore engineering become more and more important. In this paper, we complete the ultimate strength analysis by the ANSYS software.Being a generally-used software, ANSYS has a vast foreground in the structure analysis of jacket platform. Firstly, a three-dimensional finite element model of the platform in original design was built with ANSYS software. And then, static and transient dynamic analysis is performed for the platform in the extreme wave condition. The displacement-time,velocity-time and acceleration-time interval curve can be obtained. Secondly, the ultimate strength value of the platform in the original design is obtained by the nonlinear analysis, using the ANSYS program. The platform may be damaged during its lifetime. Thus, the ultimate strength are studied nonlinearly, when the damages such as corrosion, foundation eroded, brace fractured occurs in the structure of the platform. In this way, a basis for the safety assessment of offshore platform can be provided. With these research works, some conclusions can be drawn, as the following:1. Considering nonlinear material, ultimate strength of the platform structure are studied by using ANSYS. Different damage conditions are simulated such as corrosion, foundation eroded and brace fractured of the platform. And the ultimate strength is analyzed in these conditions. So the reserve strength ratio(RSR) of platform are obtained. According to the results of analysis, conclusions can be made that the ultimate strength of platform varied more greatly in the case of platform corroded and brace fracture. But it varied little when foundation is eroded.2. Ultimate strength of jacket platform varies with the direction of environment load. According to the results of analysis, ultimate strength of jacket platform in Y direction is the minimum, which is the most inferior status for the platform.3. By ultimate strength analysis at various conditions, the collapse of platform is caused by breakage of pile leg. And the brace breakage can also decrease the strength of the platform. Therefore, the key point to improve the reserve strength ratio of platform is to improve strength of piles. And then to enhance the brace, so as to promote the integrity of the jacket.