ABSTRACT

Emergency anchoring is one of the main causes of damage to submarine pipelines and one of the main factors to be considered in the design of pipeline protection. Based on the existing regulatory requirements and literature review, and combined with engineering experience, this paper systematically proposes a design method for the burial depth of submarine pipelines. First, factors to be considered in the design of pipeline burial depth are analyzed, and the general process of burial depth design is proposed. In the method, the burial depth is determined by summing up the penetration depth of emergency anchoring, the depth of seabed scouring and the safety margin. Second, calculation methods of the impact velocity and the penetration depth of dropped anchors during emergency anchoring are introduced. A finite element model to predict the penetration depth of dropped anchors is also introduced. Then, a finite element method to simulate the anchor dragging process is proposed. It is based on the equivalent chain method, in which the equivalent cylinder is identical to the actual anchor chain in terms of mass, length and bearing capacity. Finally, the proposed method is applied in a real engineering case, which shows a good applicability of the method. The proposed method is of certain significance for the design of the submarine pipeline burial depth.

INTRODUCTION

Submarine pipelines are widely used in offshore oil and gas transportation due to their high efficiency and large capacity (Bai and Bai, 2005). However, anchoring, fishing and other human activities pose a serious threat to their structural safety. Statistics show that the third-party damage such as anchoring is one of the main causes of submarine pipeline failure in China, accounting for 33% (see Fig. 1) (Wang and Liu, 2017). These failures may lead to oil and gas leaks and pollution of the maritime environment, so submarine pipelines should be properly protected from third-party damages (Xie et al., 2006).

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