Strain Based Design for Buried Steel Pipelines

管道是石油和天然气从资源所在地到市场最经济的运输方式之一。它们是影响加拿大能源行业和整体经济的关键因素。能源管道的设计是为了长距离输送加压的高度易燃物质，因此，管道的安全在基础设施的整个生命周期中至关重要。为了将对环境和温度的影响降至最低，加拿大的大部分管道都埋在地下。在运行过程中，管道通常承受由内压引起的周向应力和外部载荷/变形引起的纵向应力的组合。这些外部荷载/变形主要是土壤运动和温度影响的结果。对于这种复杂的组合加载条件，通常采用应力设计法进行设计。然而，由于埋地管道在内外载荷/变形作用下各种极限状态的复杂性，应力设计方法无法满足管道设计、维护和运营的需要。为了识别埋地管道在复合荷载作用下的各种极限状态，提出了基于应变的设计方法。临界屈曲压缩应变和拉伸断裂应变能力都将包括在内。在以往研究的基础上，埋地管道的后屈曲行为已显示出显著的储备能力和屈曲后的独特行为。在基于应变的设计中考虑屈曲后强度将产生更经济、合理和安全的设计。本计划将研究各种参数，包括不同等级的钢材、直径与厚度(D/t)比、内部压力、外部载荷、环缝、腐蚀、缺陷(或凹痕)和冷弯。识别埋地管道在各种组合载荷条件下的极限状态，并提出相应的应变极限。针对埋地管道恶劣的环境和不可预测的运行条件，提出了一种基于概率的管道安全运行风险评估方法。在开发评估工具时，结构健康监测方法将与基于应变的设计方法结合使用。每种极限状态的特征模式将使用有限元方法进行研究和开发。研究了光纤传感(FOS)技术用于地下管道分布应变测量的可行性。最后，针对埋地管道的每一种极限状态及其独特的响应特征模式，提出了使用各种创新传感技术的结构健康监测方案。

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.