The effect of internal pressure on the longitudinal behaviour of pipelines

管道是石油和天然气从资源所在地到炼油厂的最重要的运输方式之一。他们是加拿大经济中有影响力的一部分。为了实现其设计目标，管道必须安全输送高压易燃物质。在此过程中，管道需要承受由内部压力引起的周向应力和由外部负载引起的纵向应力的组合。这些外部荷载主要是土壤运动和温度影响的结果，两者都是由加拿大恶劣的环境引起的。由于管道穿越了加拿大境内大量的不连续多年冻土区，因此由于季节温差大，导致纵向应力大，管道受到不同程度的沉降。此外，管道通常需要穿越各种水路和道路以及不同的地表地形。这些位置可能会有纵向管道变形的集中，因此它们对管道的安全设计非常关键。该建议解决了当前加拿大设计准则中三个方面的问题，其中规范方程没有考虑管道内部压力和纵向响应之间的相互作用。******目前的管道应力设计规范方程没有考虑到新开发的高强度钢（HSS）的复杂材料特性。在第一个领域，我们建议提供新的方程，允许正确设计抗纵向载荷和内部压力的高速钢。同样，对于基于应变的环焊缝缺陷管道设计，规范方程没有考虑内压的影响。然而，我们以前的结果表明，依赖于临界纵向应变的水平内压。因此，我们建议使用数值模型进一步研究临界纵向应变与内压之间的相互作用。我们的长期目标是提供描述这种依赖关系的方程。在第三个领域，我们建议研究管道在不同水平内压作用下的后屈曲行为。我们希望能够提供描述后屈曲阶段所需降压水平的方程，从而确保管道的安全运行，直到褶皱或屈曲被消除。*******我们的项目对加拿大的管道行业有很大的影响。我们的项目结果将被管道行业用于在加拿大地下数千公里管道的设计和运营中做出明智的决策

Pipelines are one of the most important modes of transportation for oil and gas from the location of the resources to the refineries. They constitute an influential part of the Canadian economy. To achieve their design objective, pipelines have to safely transport a highly pressurized flammable substance. In doing so, pipelines need to sustain a combination of circumferential stresses due to the internal pressure and longitudinal stresses induced by external loads. These external loads are primarily the result of soil movement and temperature effects, both induced by the harsh Canadian environment. As the pipe traverses areas of discontinuous permafrost abundant throughout Canada, it is subjected to differential settlement exacerbated by the large seasonal temperature differential which induces large longitudinal stresses. In addition, the pipelines are usually required to cross various water and road ways as well as varying surface topography. The locations of these can potentially have a concentration of longitudinal pipe deformation deeming them very critical for a safe pipeline design. This proposal addresses three areas in the current Canadian design guidelines in which the code equations do not consider the interaction between the internal pressure and the longitudinal response of the pipeline. ******The current code equations for the stress based design of pipelines do not consider the complex material properties of the newly developed high strength steel (HSS). In the first area, we are proposing to provide new equations that would allow the proper design of HSS against longitudinal loading and internal pressure. Similarly, the code equations do not consider the effect of the internal pressure for the strain based design of pipelines with circumferential girth weld flaws. However, our previous results suggest the dependency of the critical longitudinal strain on the level of internal pressure. We are therefore proposing to further investigate the interaction between the critical longitudinal strain and the internal pressure using numerical models. Our long term objective is to provide equations to describe that dependency. In the third area, we are proposing to study the post-buckling behaviour of pipelines under the effect of various levels of internal pressure. We are hoping to provide equations that describe the required level of depressurization in the post-buckling phase allowing the safe operation of the pipelines until the wrinkle or buckle is removed.*******Our project has a large impact on the pipeline industry in Canada. The results of our project will be used by the pipeline industry to make informed decision in the design and operation of the thousands of kilometers of pipelines buried under the Canadian soil.**