The Energy Pipelines Cooperative Research Centre (CRC) is a collaboration between the members of the APIA Research and Standards Committee and researchers at the Universities of Adelaide and Wollongong, Monash University and the Australian National University.
The Energy Pipelines CRC’s mission is to deliver knowledge to the pipeline industry that will extend the life of existing natural gas pipelines, and help build the next generation of gas and other energy fluid pipelines. The transfer of this knowledge will also help with the upskilling of and the flow of people into the industry.
- The research work of the Energy Pipelines CRC is divided into four programs, which are:
- More efficient use of materials for energy pipelines;
- Extension of safe operating life of new and existing energy pipelines;
- Advanced design and construction of energy pipelines; and,
- Public safety and security of supply of energy pipelines.
The Energy Pipelines CRC has a broad program of research, currently 31 projects, tackling issues and providing fundamental knowledge in each of these areas. The remainder of this article discusses progress in one of these areas related to the design of pipelines.
Addressing fracture propagation
Fracture propagation is a significant issue for pipelines transporting gases, and the need to arrest a running fracture in a pipeline is paramount to the integrity and safety of the pipeline in operation. Full-scale tests to investigate the decompression behaviour of line pipe and provide data on the required fracture-arrest toughness are experimentally difficult and prohibitively expensive, unless undertaken as part of a large construction project.
The impracticality of carrying out large numbers of full-scale tests led to the development of semi-empirical models, such as the Battelle Two Curve model (BTCM), used to evaluate the toughness needed to arrest a propagating fracture. These models are very useful in predicting required minimum toughness levels. However, the BTCM has not been validated for the smaller diameter, thinner-walled pipes used in Australia, and the Charpy V-notch tests used to determine the required arrest toughness may not provide a good prediction for higher strength grades of steel.
Software such as GASDECOM has been developed to model the velocity of the decompression wave in the pipeline. However, recent work has shown that the frictional effects caused by the internal roughness of the pipeline can increase the toughness levels needed to arrest the fracture in a smaller diameter pipe compared to those for larger diameter pipelines under the same conditions. These diameter and roughness effects are not taken into consideration by GASDECOM and the BTCM.
All of these issues apply to both natural gas pipelines and to pipelines that will have to be built in future to transport carbon dioxide, should carbon capture and storage become adopted in Australia.
To enhance the knowledge in this area, the Energy Pipelines CRC is undertaking a significant program of work with Dr Cheng Lu at the University of Wollongong, developing models and databases predicting decompression velocities as a function of pipeline diameter, internal roughness and gas composition for both natural gas and carbon dioxide pipelines. These models are being validated against data generated in shock-tubes tests, which provide experimental data for decompression wave velocity at a fraction of the cost of a full-scale fracture-arrest test.
Compared to the shock-tube experimental results, the models developed by the Energy Pipelines CRC predict better decompression wave velocities than the commonly used softwares, such as GASDECOM. It has been found from the Energy Pipelines CRC models that the pressure–decompression wave velocity relationship depends on the location in the pipe, which is consistent with the shock-tube observation. However, GASDECOM is incapable of predicting this phenomenon.
The outcome of this work will allow the prediction of material requirements, determined in laboratory scale tests, to ensure the arrest of a propagating fracture in service. This in turn will lead to enhancements in pipeline design practice and a better understanding of the behaviour of new gas mixtures.
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