Study On Load Of Subsea Valve

As an important part of submarine pipeline system,the subsea valve is widely used in the offshore oil and gas engineering,underwater pipeline,marine pipeline terminals and oil and gas pipelines.Once the subsea valve failure,the loss can't be estimated.Because the marine environment is particularity,and the investment in marine equipment is high and it is hard to maintain the marine equipment.Therefore,it is of great significance to analyze the loads of subsea valve.According to the working conditions of subsea valves and combined with the relevant standards of submarine pipelines,the paper summarized the types of loading of subsea valve and determined the combination of subsea valve loads.Matlab software was used to analyze the influence factors of wave force.The finite element software was used to analyze the natural frequency and mode of the subsea ball valve,which provided a reference for the modal analysis of the subsea valve.The main research work of this paper was following.First of all,on the basis of the types of the submarine pipeline,combined with the actual working environment of the subsea valve,the load types of the subsea valve were characterized by functional loads,environmental loads and accidental loads.Environmental loads have loads of currents,waves and earthquake.Functional loads have weight,the external pressure,internal pressure,the reaction forces of pipeline and bottom bearing.Accidental loads have a fire,explosion,sudden pressure drop,falling objects,third party equipment,etc..There were 2 kinds of load combinations of the subsea valve:(1)functional loads + the environmental loads;(2)functional loads in working condition + the earthquake loads.Unless accidental loads are predicted to occur at the same time,it is not considered to be combined with other loads.Secondly,it is known that the linear wave theory and stokes five order wave can be used to describe the wave motion in the deep water environment.Due to the small size of the valve structure,the current force and wave force are solved to the Morrison equation.The influence of water depth,period and wave height on the wave force of subsea valve was calculated by using Matlab software,which was based on the theory of linear wave and stokes five order wave theory.The results showed that the smaller the water depth,the higher the wave height,the greater the cycle,the greater the wave force of the valve.The influence of the installation depth on the wave force of the valve is analyzed,and the horizontal wave force is larger than that of the vertical wave force.The wave force decreased with the increase of depth in the installation process.Finally,two modal analysis methods of subsea valve were analyzed.The finite element software was used to simulate and analyze the natural frequency and vibration mode of subsea valve with the dry modal method and wet modal method.The results showed that the wet modal analysis results were more accurate and more suitable for subsea valve modal analysis.Based on the seismic analysis of the submarine pipeline and the seismic analysis of the onshore valve,it can be seen that the seismic analysis methods of the subsea valve have the limit seismic stress method,the equivalent static method and the transient dynamic analysis method.The method of transforming the pseudo acceleration spectrum into time history acceleration curve was analyzed.Under the design pressure,dead weight,external hydrostatic pressure,bolt(screw)pre-tightening forces and seismic load(SSE),static analysis of a subsea ball valve was an example to analyzed.The analysis results showed that it had good seismic performance under SSE load.