THE DECOMPRESSED STRESS LEVEL IN DENSE PHASE CARBON DIOXIDE FULL-SCALE FRACTURE PROPAGATION TESTS

A total of nine full-scale fracture propagation tests with liquid or dense phase carbon dioxide (CO2) have been conducted by four research projects: CO2PIPETRANS, COOLTRANS, SARCO2B and CO2SafeArrest. The semi-empirical Two Curve Model assumes that steady-state ductile fracture propagation can be described using an effective crack length. It was shown that a normalised effective crack length that separated the arrest and propagate data points from full-scale tests with subcooled water, water-air or gas could be defined on a plot of the normalised decompressed stress level (the hoop stress at the crack tip) versus the normalised toughness. DNV-RP-F104 September 2021 Design and operation of carbon dioxide pipelines introduced a simple empirical model for establishing whether or not a running ductile fracture would arrest in a pipeline transporting liquid or dense phase CO2. The empirical model is also based on the aforementioned plot, but with data points from full-scale tests with dense phase CO2. COOLTRANS and CO2SafeArrest have collaborated in a reanalysis of the raw data from each of their respective full-scale tests. A re-plotting of the data points confirms the appropriateness of the empirical model in DNV-RP-F104. It also provides an insight into a possible difference between the effective crack length for natural gas, and for liquid or dense phase CO2.