While there are hundreds of mile-years experience with CO2 pipelines, some is still unknown. US PHMSA incident experience. Compared to most hydrocarbon pipelines, with hundreds of thousands of mile-years experience, CO2 pipelines are relatively new. Many risk issues are the same but a few are notably different.
- hydraulics, corrosion rates, and toxicity are all significantly influenced by even minor amounts of non-CO2 components commonly seen in the product stream
- even for pure CO2, corrosion rates when water is introduced can be extremely high
- most efficient transport state–above ‘triple point’ (ie, supercritical)–makes product behave in ways not yet fully model-able in real application
- extreme temperature effects experienced during phase changes can affect material properties (resistance)
- dispersion modeling for CO2 is less validated and lacks, for example, complete understanding of contributions from sublimation of solid CO2 (dry ice).
As one example of unusual risk issues, consider a pinhole leak from a CO2 pipeline. As with all pipelines, such small leaks are very difficult to detect and may persist for some time. Under the right conditions, this small CO2 leak may create an highly corrosive acidic environment around the exterior of the pipeline–leaking CO2 dissolving in ground water forming carbonic acid. Extreme, yet plausible, corrosion rates associated with steel in contact with carbonic acid could result and significant metal wall loss could occur in months.
