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The proposed pipeline is located in a discontinuous permafrost area and designed to transport chilled gas with a mean annual gas temperature below 0°C. The combination of discontinuous permafrost areas and large diameter chilled gas pipelines presents challenges for pipeline design, construction, operation, and maintenance, as well as environmental protection. To adequately design the pipeline, TransCanada has developed and applied an innovative engineering design methodology over the last ten years. The engineering design methodology was submitted to and accepted by EUB which represents the first time in the onshore pipeline industry that an alternative design methodology for large diameter chilled gas pipeline received explicit regulatory acceptance.
"Designing a pipeline in discontinuous permafrost areas presents unique challenges," says Joe Zhou, technology leader on the project. "But it offered us the perfect opportunity to introduce the new methodology."
The Methodology
Large diameter pipelines in discontinuous permafrost areas induce differential frost heave and thaw settlement due to alterations to soil temperature. The differential frost heave and thaw settlement in turn cause strain accumulated in pipe material potentially to such magnitudes that conventional stress-based design methodology is inadequate to deliver a safe and cost-effective design. Based on extensive research and technology development, TransCanada has developed an innovative strain-based design methodology and integrated design process where:
- The pipeline safety and integrity are maintained with cost-effective means in design, construction, and integrity management processes.
- Strain demands induced by differential frost heave and thaw settlement are reliably predicted with an integrated engineering model that simulates adequately the gas hydraulics, geothermal behaviour, pipeline structural response and their mutual dependencies.
- Strain capacities are fully explored and utilized based on pipe material property, welding process and procedure, and inspection.
- Optimization based on life-cycle cost is readily achievable across engineering disciplines, project components, and capital cost vs. operating cost.
This innovative design methodology is expected to deliver significant cost saving to large diameter pipeline projects in discontinuous permafrost areas while maintaining adequate safety over the entire operating life of the pipelines.
The new design methodology will benefit TransCanada by helping facilitate the filing of routine applications with the EUB, realizing significant cost savings during the project's life cycle and assisting in the design of future northern pipeline projects.
For Information
For more information on the new Engineering Design Methodology, please contact Joe Zhou at 403.920.7227.
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