Advances in High Strength Technology for Natural Gas Transmission

Andrew K Jenkins and Alan G Glover TransCanada PipeLines Ltd

Calgary, Alberta, Canada

ABSTRACT As the demand for natural gas as a prime global energy source continues to grow, the search for new sources of the fuel spreads into geographical areas that are more remote from the marketplace. Along with this comes the need for longer and ever more efficient pipelines. This requirement for higher value in natural gas transportation is satisfied to a large extent through the application of high strength technology and innovative design approaches that support increased design and operating pressures. This paper reviews the latest accomplishments and successes in these technologies for use in gas transmission. It also explores some of the technologies which are targeted for the future to allow the industry to achieve even higher benchmarks in reliability and cost-effectiveness. The central element in the theme of high strength technology for gas pipelines is that of high strength steel. From tensile strengths of Grade 359 a few decades ago, more and more operators are now specifying Grade 550 linepipe for their large diameter projects. As well, Grade 690 steel is operating successfully in limited transmission applications and Grade 825 has recently been installed. With the introduction of the latest high strength pipe comes the need for high strength fittings. The industry’s first Grade 550 fittings were recently specified and installed on a project with Grade 825 line pipe. High strength materials can only be implemented successfully if compatible design and construction processes are in place. The latest developments in strain- and reliability-based design will be described as well as the corresponding advancements in welding and inspection technology. KEY WORDS: High strength steel, Pipelines, Fracture, Welding, Strain-based design INTRODUCTION Traditionally onshore gas pipelines have been designed using a stress-based approach, which provides a safe and conservative methodology. At the same time the operating environment of pipelines is facing increasing challenges. In 1910 the operating pressure of a gas pipeline

was 200 kPa (30 psi) and the diameter was 406 mm (NPS 16). In 2002 the typical operating pressures of an onshore gas pipeline are 12000 kPa (1740 psi) and higher, in diameters up to 1422 mm (NPS 56). The trend of changing pipeline pressures is shown in Figure 1. Not only

Figure 1 Increasing operating pressure trend have pressures changed (and are continuing to increase) but also the regions in which gas developments occur are becoming more remote and in more hostile environments. Discussions on development of gas reserves in the North American arctic have been ongoing since the 1970s, and many factors have slowed or delayed those developments. One of the reasons that the pipelines have not been built is because previous studies have always found the cost too high to make the pipeline economically justified. In recent years changes in pipeline design and construction technology have the potential for reducing the cost of these Northern pipelines substantially. TransCanada PipeLines (TCPL) in conjunction with major pipe manufacturers and other major companies have been working on various pipeline technologies that will contribute towards these reductions in costs. The prime impetus for increasing pressure in a gas pipeline system and related increases in material properties is economics. On a large diameter pipeline project in North America about 40% of the project cost is related to material, (in a Northern project about 30% of the cost

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