Theoretical Analysis And Experimental Study Of Thermally Insulated Subsea Pipelines

Subsea pipelines are the crucial link between oil and gas development and mainland as the lifelines of transportation and gathering of petroleum crude. The investment to pipeline accounts for the big part of the whole cost of oil field. It has been being a challenging subject to reduce the expenditure and maintain the good conditon of pipeline.Heat preservation measures are inevitably required in China offshore projects because most of the crude oil has high pour point and viscocity. The conventional pipe-in-pipe structure consumes steel material too extravagantly because near 2/3 steel is used by the outer pipe, which only acts as the protect coat and heat preservation, although it may be capable of the task. Moreover, this tradional pipe increases the the cost on construction because the welding work is quite time consuming and maintain cost is very high. Considerable amount of steel can be saved using thermally insulated pipeline, where the outer steel pipe is substituted by heat insulated layer and jacket. It is self-evident that faster laying speed is anticipated because only single layer steel pipe is needed to weld. Referring to the foreign experiences and research results, a lot of experiments and threotical study have been carried out. Based on two practical engineering projects, this paper aims to accelerate the development and application of this new type pipeline in China by directing the engineering projects.Laboratory tests have been lauched to investigate the compress and shear strength of heat preserving material. Full scale specimens were adopted to measure the shear strength between layers and compress strength of the pipe. Furthermore, the experiments carried on the laying barge were the preview and simulation of pipe laying. Some phonomena occurred during the tests have been explained from the view of therotical analysis and numerical calculation.Referring to available research results, pipe laying analysis has been performed and solution has been obtained using a singular disturbation method. The results were implemented into program code within a Newton-secant iteration framework. The configuration and stress of the pipeline can be achieved with this program. A serial of calculation models were introduced and simple equations has been acquired to check the shear stress between layers of pipeline during both laying and operation period. Simulation of pipeline in tensioner was carried out with FEM software to check the safety factor. Both linear and nonlinear buckle analysises have been performed to calculate the safety status under hydrostatic pressure. The hoist of elbow has been optimized by comparing three schemes with FEM analysis. The research progress of pipe soil interaction has been retropested.The UWPAPIPE models were improved and implemented into a structure analysis program as macroelemet. The pipeline response was examined due to hydrodynamic load with the program to study the influence of the span length. Prospective widely application of thermally insulated pipeline is anticipated since it has the unique advantages. However, thermally insulated pipeline is still immature with total 2-3 finished pipelines in China. Therotic study practical construction experience is anticipated to intensify. This thesis could be taken as a summary of experiment analysis and theoretical stuy of the beginning application of thermally insulated pipeline in China. The author humbly hopes all these could provide some references to prospective researchers.