Strain Based Design for Buried Steel Pipelines

点击翻译按钮获取中文摘要

Pipelines are one of the most economical modes of transportation for oil and gas from the location of the resources to the market. They are a key factor influencing the Canadian energy industry and overall economy. Energy pipelines are designed to transport pressurized highly flammable substances over a long distance, therefore, safety of the pipelines is paramount throughout the life of the infrastructure. To minimize the environmental and temperature effects, most of pipelines in Canada are buried underground. During the operation, pipelines are normally sustained a combination of circumferential stresses due to the internal pressure and longitudinal stresses induced by external loads/deformations. These external loads/deformations are primarily the result of soil movement and temperature effects. The stress design method is normally used to design these complex combined loading conditions. However, due to the complex nature of each ultimate limit state of a buried pipeline under internal and external loads/deformations, the stress design method is unable to address the needs of pipeline design, maintenance and operation. The strain based design method is proposed here, in recognizing various ultimate limit states of a buried pipe under combined loading conditions. Both the critical buckling compressive strain and tensile fracture strain capability will be included. The post-buckling behaviour of a buried pipe, based on the past research, has shown significant reserve capacity and unique behaviour after buckling. The inclusion of post-buckling strength into the strain based design will yield a more economical, rational and safe design. The various parameters will be investigated in this program, including different grades of steel, diameter to thickness (D/t) ratios, internal pressures, external loads, girth welds, corrosion, defects (or dents), and cold-bend. The limit states of a buried pipe under various combined loading conditions will be identified and corresponding strain limits will be proposed. Due to the harsh environmental and unpredictable operational conditions of a buried pipeline, a probability based risk assessment is proposed for a safe operation of a pipeline. Structure health monitoring methodology will be used in conjunction with the strain based design methods in developing the assessment tool. The signature patterns of each limit state will be studied and developed using the finite element method. The feasibility of using fibre optic sensing (FOS) technology in measuring distributed strains of a buried pipe will be investigated. Finally, structural health monitoring programs using various innovative sensing technologies will be proposed for each limit state of a buried pipe and its unique responding signature patterns.