Help Close a Critical Knowledge Gap in CO₂ Pipeline Integrity
A pipeline design can only be as reliable as the assumptions behind it. For one new carbon dioxide transportation project, the expected CO₂ stream included a combination of impurities that could change how the fluid may decompress during a rapid pressure release.
The project team needed more than data from pure CO₂ decompression behavior; t needed evidence that reflected the exact expected fluid properties for the proposed pipeline.
Designing Beyond Pure CO₂
Carbon capture projects rarely produce a pure CO₂ stream. Depending on the capture process and source, the transported CO₂ may contain small amounts of other impurities, including NOx, SOx, H2, Benzene, CO and others.
This matters because mixture composition, operating pressure and temperature affect decompression behaviour of the fluid. It is very important to understand this decompression behavior in detail, to allow the pipeline designer to select appropriate pipe wall thickness, material toughness and fracture-control measures, to ensure that if there is ever a rapid release, any pipeline fracture will quickly arrest rather than propagate.
Looking Beyond Historical Data
Pipeline designers often use models to predict decompression behaviour. These tools are essential, but their accuracy depends on whether they have been validated for the mixture and operating conditions being assessed.
For the clients proposed pipeline, the full combination and concentration of expected impurities had not been extensively modelled previously. Thus, relying only on theoretical predictions would have left the design team without the project-specific evidence it needed to reduce uncertainty to an acceptable level.
One alternative may have been to make very conservative assumptions, such as specifying greater wall thickness and material toughness to account for the uncertainty. This approach may reduce risk, but will at significant cost.
Creating Real-World CO₂ Stream Conditions in a Controlled Environment
For this project, C-FER worked with the project stakeholders to define the expected range of impurity concentrations, develop the test program, and assemble the technical team required to carry it out. The objective was to reproduce a range of possible representative CO₂ mixtures and measure how they decompressed under controlled conditions.
For each test, a mixture was prepared and then injected into a shock tube, which essentially is a long, heavily instrumented section of pipe designed to safely contain the mixture at pipeline-relevant conditions. Each mixture was slowly pressurized at a controlled temperature, until a release device at one end of the shock tube activated, initiating a rapid decompression wave that travelled through the tube. Fast-response pressure transducers positioned along the shock-tube length captured the pressure changes in real time.
Capturing useful data required closely spaced instrumentation, high-speed acquisition and careful control of gas composition, pressure and temperature. The team also developed methods for introducing and handling fluids with different physical hazards, while working within the practical constraints of an outdoor test facility.
Strengthening Analytical Models
The physical tests were not intended to replace engineering analysis, but instead to inform it.
For each condition, the team converted the pressure measurements into experimental decompression curves and compared them with theoretical predictions. This allowed the engineers to assess how well various equations of state represented the observed behaviour and to identify where experimental effects differed from predictions.
The comparison gave the designers a stronger basis for applying and refining appropriate models for the proposed pipeline. It also demonstrated the value of using testing and modelling together: models helped shape the test matrix, while the test results provided evidence for checking and refining the analytical approach.
Turning Test Data Into Design Decisions
The test program provided the project team with the decompression data needed to support key decisions involving pipe toughness, wall thickness and fracture arrest. The work replaced generic assumptions with an evidence-based design basis. The team could explain what pipeline design parameters were selected, and why they were appropriate for the expected service conditions.
For emerging CO₂ infrastructure, a design based on properties of pure CO₂, a historical project or the nearest available mixture may not represent the actual interaction among composition, pressure and temperature. As well, the evidence from one test program does not automatically answer every future design question. Another pipeline section may operate at a different pressure or carry a different combination of impurities. Those changes can alter decompression behaviour and require a new evaluation.
For pipeline designers and operators, shock tube testing provides a practical path from “this mixture should behave similarly” to “this design is supported by evidence that reflects our application.”
How C-FER Helps Operators with CO₂ Challenges
C-FER combines test-program design, full-scale experimental experience and engineering analysis to help project teams resolve CO₂ pipeline design uncertainties.
By connecting representative testing with engineering analysis, C-FER helps project teams move from uncertain assumptions to defensible pipeline design decisions.
Contributor
Kelly Piers, MSc, PEng.
Principal Engineer, Business Development & Strategic Initiatives
Kelly Piers is a Principal Engineer at C FER Technologies. In this position, Kelly works on strategic and business planning for C-FER and focuses on identifying, developing and implementing C-FER’s strategic diversification objectives, working with a number of industry associations in Alberta and across Canada.
