Analysis of seabed stability and local scour around submarine pipelines under waves and current

For the safety issue of laying and operation of submarine pipelines in deepwater oil exploitation and gas mining, the available theoretical and empirical methods were employed, besides, a relationship between the equilibrium local scour depth and the corresponding spanning length was deduced under current condition. Based on this work, an analysis program was developed, using a mixed-language programming technique which involves Fortran and Visual Basic. The sand stability and the local scour around submarine pipelines were predicted for a practical engineering application in South China Sea. The actions of current, waves and combined waves and current were considered in this work. The stability of seabed before laying pipeline was evaluated using the proposed code, the maximal local scour depth, lateral growing speed and the transition time associated with the local scour were also presented. The results show that the current action takes a decisive role for the bed stability in deepwater region; and a small particle size of bed sediment will contribute a large viscosity which will reduce the pipe erosion rate of expansion. This analysis provides a technical basis for the design of submarine pipeline routings and the formulation of construction schemes.