Two full-scale fracture propagation tests have been conducted using dense phase carbon dioxide (CO2)-rich mixtures at the Spadeadam Test Site, United Kingdom (UK). The tests were conducted on behalf of National Grid Carbon, UK, as part of the COOLTRANS research programme.
The semi-empirical Two Curve Model, developed by the Battelle Memorial Institute in the 1970s, is widely used to set the (pipe body) toughness requirements for pipelines transporting lean and rich natural gas. However, it has not been validated for applications involving dense phase CO2 or CO2-rich mixtures. One significant difference between the decompression behaviour of dense phase CO2 and a lean or rich gas is the very long plateau in the decompression curve.
The objective of the two tests was to determine the level of ‘impurities’ that could be transported by National Grid Carbon in a 914.0 mm outside diameter, 25.4 mm wall thickness, Grade L450 pipeline, with arrest at an upper shelf Charpy V-notch impact energy (toughness) of 250 J. The level of impurities that can be transported is dependent on the saturation pressure of the mixture. Therefore, the first test was conducted at a predicted saturation pressure of 80.5 barg and the second test was conducted at a predicted saturation pressure of 73.4 barg.
A running ductile fracture was successfully initiated in the initiation pipe and arrested in the test section in both of the full-scale tests.
The main experimental data, including the layout of the test sections, and the decompression and timing wire data, are summarised and discussed.
The results of the two full-scale fracture propagation tests demonstrate that the Two Curve Model is not (currently) applicable to liquid or dense phase CO2 or CO2-rich mixtures.