Stability Analysis Of In-situ Submarine Pipeline

Submarine pipeline is a major component of the offshore oil and gas field production system, it plays a significant role in the development of offshore oil and gas resources, which has been hailed as the "lifeline". Safe and efficient operation of submarine pipeline is important to ensure normal production of oil and gas fields. To ensure the safe operation of the submarine pipeline and avoid the failure accidents of submarine pipeline, the security of submarine pipeline in period of service has become a major focus of the international oil companies.With the increasing depth of oil and gas development, deepwater submarine pipeline faces many new challenges. In this paper, the submarine pipeline settlement formulas are investigated, and the calculation methods of pipeline installation settlement are also studied. By studying the relationship of the formulas method and the numerical simulation method, and connecting with engineering experience, the paper proved the reliability of the theoretical analysis and numerical analysis. In the end, the pipeline- soil interaction frictional resistance curves are given. The analytical solution of thermal buckling in vertical and lateral direction was deduced, the numerical solution was put forward in the simulation of thermal buckling and the difference and contact between the analytical solution and numerical simulation were compared. This paper aslo analyzes the protection measures of thermal buckling in vertical and lateral direction, analysis the mechanism of thermal buckling under the protection of concrete block and mattress and the sleeper condition, compare the effect of two methods. The ARVM model which is used in the landslide stability analysis is established and the sensitivity analysis of key factors calculation kernel and hyper-parameter value is carried out. Concrete interlocking blocks are designed for avert the negative effects of scouring. The stability of concrete interlocking blocks and scouring defending effect is assessed by FEA calculation and model tests, and the optimal design of concrete interlocking blocks is proposed based on the analysis results. The submarine pipeline detection and maintenance methods and the applicable scopes are introduced, and the process and steps of submarine pipeline detection and maintenance are also given, which are combined with engineering example. The conclusions are as following:(1)The diameter and weight of submarine pipeline have more significant influence on the settlement, which is inversely proportional to the diameter and proportional to the pipe weight. Undrained shear strength of soil also can not be ignored, as with the increase of soil strength, pipeline settlement exponential attenuation. When the strength of soil is higher than 2k Pa, the pipeline settlement gradually reach the same value. The settlement caused by installation is greater than the self-settlement. The settlement is bigger than one quarter of pipe diameter, and less than the pipe diameter. The gulf of guinea and Angola sea engineering experience and the actual observation data proved the reliability of the result.(2)The buckling deformations were developed based on the geometric morphology of initial imperfection both for vertical and lateral buckling, the axial stress(strain) and axial force on the midpoint of the pipeline were the biggest; comparing to the numerical solution, the critical temperature calculated by analysis solution is much bigger than that calculated by numerical solution, the biggest diference is about 20 %.(3)In the protection technique of sleeper methord, the greater of the amplitude of initial imperfection, the critical buckling force of the pipeline is smaller, and with the increase of the initial imperfection, there are less effects of the wall thickness on the critical buckling force. Under the same condition of wall thickness, with the increase of the spacing of two sleepers, the critical buckling force decreases gradually.(4)The ARVM landslide stability analysis model can quantify the state of the slope stability, and the predictive accuracy is related to the calculation kernel and hyper-parameter value. The pilot calculation should be applied as a compromise to find the optimal width value. The current is complex in the heads of concrete interlocking blocks. The dynamic water pressure of heads of concrete interlocking blocks is largest in the surface against the current, and these blocks have a tendency to set off. The blocks which local on both sides should increase the thickness or be designed into streamlined to reduce the impact of the current.(5) The submarine pipeline detection and maintenance methods and the applicable conditon are introduced, and the process and steps of submarine pipeline detection and maintenance are also given, which are combined with engineering practice.