Study On Dynamic Characteristics Of Subsea Pigging

With the rapid development of China’s offshore pipeline construction and the requirements of pipeline integrity management,pipeline pigging technology has been placed in an important position.The subsea pipelines are in a complex and bad sea environment,and under the complicated stresses for a long time,so there are many risks in the process of subsea pigging.In particular,the blocking and bypass of the subsea pipelines will seriously affect the safety and efficiency of pigging,and this two problems are urgently to be studied and solved.This article studied the dynamic characteristics of the subsea pipeline pigging from two aspects of friction resistance and bypass that have great impact on pigging.Firstly,the motion process of the pig is analyzed.The movement of interference spherical pig is translational,and the non-interference pig is rolling.However,the actual motion state of disc pig and cup pig is generally maintained translational forward motion with some irregular rotation.And compared to the saucer-shaped cup pig,the conical cup pig has a better performance of passing and adaptability.In addition,the expanding of diameter changing valve has important influence on the movement of pigs.An analysis of the influence of the physical properties of the PUE(Polyurethane Elastomer)body on pig’s dynamic characteristics is made and a mathematical force model of the pig is established.The calculation methods of the radial extrusion force and frictional resistance of three kinds of pigs in horizontal pipe section is derived by mechanical formulas.Especially in the analyze of disc pig’s stress,the problem of inertia moment of variable cross-section cantilever beam is solved.And the calculation results of disc pig are compared with the field test.By contrast,the error is less than 15%,within a reasonable range.According to this method,the friction resistance can be estimated before pigging,which can provide theoretical support for the pigging plan and the selection of the pigs.Numerical simulation is carried out on the bypass characteristics in the operation of pigging using Fluent 2D transient dynamic grid technique.The development and change of the bypass fluid and its influencing factors are analyzed.The bypass characteristics and sealing performances of the foam pig and spherical pig are compared.It can be seen that there’s a clear vortex before the spherical pig due to the influence of bypass jet in the simulation,yet there’s no disturbance in the rear of the spherical pig.The velocity of the bypass flow grows slower with the increase of pressure difference,and it’s a relation of power function.Besides,the bypass flow rate of foam pig is much less than that of the spherical pig at the same bypass rate condition.So the sealing effect of the foam pig is better,and the movement is more stable.