This paper presents the method to perform cutting of welding groove for intersecting of pipes at small angle during Liwan 3-1 CEP jacket fabrication. The mathematical model of the intersecting pipes as well as the cutting method for transition section have been studied using the principle of geometry, which enables fabrication team to print out the full scale template drawing to guide cutting of welding groove for intersecting of braces at small angle. This method has been fully tested during LW3-1 jacket fabrication which indicated that the welding groove can meet the requirements of AWS D1.1 code and the method can be adopted for future jacket construction.
At present, the jacket piles are lifting onto the barge by crawler crane or floating crane in domestic and overseas in traditionally methods. The piles are too heavy (normally 400t-700t each) and long (normally more than 100m long), large crawler cranes or floating cranes are usually be used in lifting. As all know, the unit price of floating cranes are expensive and much area are needed for the crawler cranes. In order to solve these problems, based on the characteristic of the piles rolling in the circumferential direction, this paper introduced a new process for the jacket piles rolling onto the barge. A suite of project auxiliary structures need to be designed to complete the whole process. The designing process for the project auxiliary structures is introduced in this paper.
LW3-1 CEP(Central Processing Platform) jacket ranks fifth heaviest jacket in the world and the heaviest in the Asia. Some of members were overheated due to improper temperature control in the PWHT process during the fabrication of the tubular members. To evaluate the impact of overheating to the member performance, a series of evaluation experiments were performed for the overheating members and repair work was conducted to replace damaged area of members. This paper summarizes the evaluating experiments result and the repair procedures for the areas which were overheated in the PWHT(Post Weld Heat Treatment) process during the fabrication of the LW3-1 jacket. The proposed repairs meet the project requirements for both strength and fatigue requirement. This paper presents the experiences which may benefit future applications.
The optimization design method of geometric parameters of skid shoe which is used to subject weight of marine structures is proposed. Considering skid shoe as steel frame structure, total weight and the bearing capacity of the skid shoe are selected as optimal objectives, and geometric parameters of the skid shoe are taken as design variables. Taking the strength, stiffness, local stability of the skid shoe as the constraint conditions, multi-objectives constraints optimization model of geometric parameters is established, and solved based on complex method. According to research results, a computer program has been developed using VC language. Then geometric optimum parameters of skid shoe in service of CNOOC are analyzed by the program. The results show that optimized design decreases steel volume, steel plate thickness by 28.7%, 18.4%, respectively, compared with original design. The optimization method has a series of advantages, such as simple model, fast calculating speed, high calculation accuracy.
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