Exposed and shallow buried submarine PIP pipelines subjected to high temperature and high pressure (HTHP) are more prone to lateral global buckling, which is an important issue in the design and in-service assessment of submarine PIP pipelines. Pipe-soil interaction resulting from pipeline movement plays an important role in the lateral buckling behavior of pipelines. In this paper, a series of lateral pullout tests were carried out on model pipe segments having a diameter of 58mm buried in sand, with different embedment ratios ranging from 0 to 1/2. Based on the observed data of model tests, a nonlinear lateral pipe-soil interaction model is proposed to describe the lateral resistance force-displacement relation. 3D finite element numerical models in which the relation of the nonlinear pipe-soil interaction is employed are established to study the lateral buckling behavior of submarine pipe-in-pipe pipelines. A combination of pipe-soil interaction elements, beam elements, and tube-to-tube elements is used in the FE models. The lateral buckling process of submarine PIP pipelines is simulated, and the influences of lateral pipe-soil interaction models, pipe out-of-straightness (OOS) and stiffness ratio of the inner pipe to the outer pipe on the lateral buckling behavior of submarine PIP pipelines are discussed. Results show that the exact pipe-soil interaction relation affects the lateral buckling responses of submarine PIP pipelines. The capacity of submarine PIP pipelines against lateral buckling increases with the increase of the embedment ratio. It decreases with increasing pipe OOS and stiffness ratio of the inner pipe to the outer pipe.
As shown in Fig. 1 referring to Zhang (2021), the PIP pipeline system consists of an outer pipe, an inner pipe, centralizers, bulkheads, and insulation material. The insulation material ensures the PIP system has exceptional thermal insulation properties. Therefore, submarine PIP pipelines have been used as one of the main means of transporting oil and gas where heat needs to be retained and minimize flow assurance risks. At high temperature and high pressure, exposed and shallow buried submarine PIP pipelines constrained by the soil resistance suffer from excessive axial force which causes pipelines to be more prone to lateral global buckling. Consequently, great attention should be paid to lateral buckling which is an important issue in the design and in-service assessment of submarine PIP pipelines.
