Study On The Submarine Pipeline-soil Interaction Under Complicated Conditions

With the exploitation of the ocean oil and gas, submarine pipeline has been the most popular way to transport oil and gas in the world for its convenience, safety and reliability. Submarine pipeline is an important part of offshore oil production system, which connects offshore oil production system, transportation system and storage system, even the offshore oil field and onshore oil field. With the development of offshore oil engineering, submarine pipelines are more and more necessary for it. Comparing with the pipe on land, most of the submarine pipelines are operated under complicated conditions, which have the more probability to be invalid. Therefore, more attentions have been paid to the safety of the submarine pipelines. As yet only a little research of this field has been done in our country. To investigate the safety and stability of the submarine pipelines is necessary and significant.A whole submarine pipeline system includes three parts: riser system, submarine pipeline and the landing pipeline. Each part of the pipeline is operated under different and complicated conditions. Concerned with the practical pipeline engineering in Bohai gulf, the stability of the submarine pipeline system is studied under the special loading and entironment conditions of this area, some new methods and suggestions are proposed:1. Based on a study of the soil-pipeline interaction, the upheaval buckling of the heated submarine pipelines buried in the seabed is studied. According to the buckling analysis of the ideal pipelines, a new method is presented to calculate the upheaval buckling of the pipelines with initial imperfections. The effects of temperature variations, soil properties, buried depth and expansion bend to the upheaval buckling have been discussed, and some available measurements have been recommended for a pipeline design.2. Owing to the complexity of the pipe-in-pipe riser system, load and restraint, many problems arise in the structural analysis of the riser. A new method to conduct nonlinear static finite element stress analysis on riser system is presented. The FE model of the risers system is built via software AutoPIPE. The effects of surrounding soil and other operation conditions are simulated by the FE method. Then based on a pipeline project an entire procedure of stress analysis is discussed in detail including creation of a FE model. Then, the effects of the location of flanges, the thermal expansion of submarine pipelines and the restraint of seabed on stress distribution in the riser and expansion loop are studied. The analysis results are valuable for pipeline designers.3. In the last of this paper, the negative effects of the reclamation engineering to landing pipelines under the bank were studied. Based on the engineering in the harbor industry area of Tianjin, the FE method and the elastic foundation beam theory were taken to analyse the stress of the pipeline under a large area surface load, then the height of the dredger-reclaimed soil will be proposed. A protection project is proposed when the seabed pipeline cross the reclamation dike, FE method were used to calculate the stress and the distortion of the pipelines under the protection in order to validate the protection project's efficiency. Then, some suggestions of the reclamation engineering were proposed to guarantee the safety of the pipelines.In the years of the paper writing, the author has participated in many different pipeline designing projects. The several new methods presented in the paper have been used in the real projects, which can satisfy the practical requirements. Therefore, the new feasible methods are supposed to the submarine pipeline design and construction.