Objective The ongoing promotion of “dual carbon” strategic goals has accelerated the design and construction of CO₂ pipelines. Long-distance CO₂ pipeline transportation typically operates in a supercritical or dense phase state, where the high medium density and complex phase behavior necessitate an urgent assessment of water hammer risks due to changes in operating conditions and equipment startup/shutdown.

Methods To clarify the water hammer characteristics of supercritical CO₂ pipelines, a transient model was developed using OLGA software, focusing on a supercritical CO₂ pipeline containing impurities in China. This study examined the water hammer issue under topographic relief and compared the results with those obtained from the theoretical formula of water hammer pressure.

Results In the CO₂ pipeline with fluctuating elevations, the lowest point was susceptible to water hammer overpressure instability or phase transition due to low pressure. To mitigate this risk during pipeline pressure design, the water column pressure at the highest elevation point should be added to the theoretically calculated water hammer pressure amplitude. Additionally, when determining the minimum operating pressure, the water column pressure at the lowest elevation point should be considered to prevent phase changes caused by water hammer negative pressure. Compared with pure CO₂, the presence of impurities with a density lower than CO₂ in the pipeline reduced the water hammer pressure amplitude and increased the water hammer period, thereby effectively mitigating the water hammer risk in CO₂ pipelines.

Conclusion In CO₂ pipeline engineering design, it is advisable to integrate the theoretical formula of water hammer with a transient simulation model that accounts for elevation to address water hammer issues, particularly focusing on the low points of the entire pipeline. In establishing impurity content indexes, it is essential to consider not only water hammer but also economic comparisons, risk evaluations (including corrosion, leakage, decompression waves, and ductile crack arrest), and a comprehensive analysis of upstream carbon sources.