This paper investigates the pressure gradient between the contact points of submarine pipeline by studying the analytical formula of pressure distribution. The study condition is unidirectional current. On this basis, the formula of seepage velocity on the seabed is derived by using Darcy's law. Besides, the critical velocity of sediment incipient motion in the wake region is obtained by analyzing the forces of particles. Furthermore, the relation of scour hole depth and velocity is obtained according to the experiment data. Compared with experimental data, authors found that the formula results shows the variation regularity of seepage and the motional law of sand.
With the development of ocean oil exploitation in recent years, submarine pipeline has become an important carrier which is extensively used to transport the oil from offshore to land. Because of the complicated ocean environment, the influence of many uncertain factors makes it very difficult to manage the underwater conditions. So the destruction of submarine pipeline have often occurred. The most important reason was that the pipeline was suspended owing to the scouring of seabed underneath the pipe. When the seepage velocity reached to critical value, the sediment starts to transport. That is the main reason for scouring. Therefore, the study of seepage velocity from which get the relationship between dynamic water pressure and seepage velocity is significant. It is the foundation for the further study of protection techniques, and will be of great value for engineering application and theory research. When the submarine pipeline is put on the seabed without a gap and covering, with the action of currents and waves local scour underneath the pipeline will happen. This part of dynamic water pressure will act on the seabed below the pipe and increase the seepage velocity.
