Ruptures in Gas Pipelines, Liquid Pipelines and Dense Phase Carbon Dioxide Pipelines

Abstract

Ruptures in gas and liquid pipelines are different. A rupture in a gas pipeline is typically long and wide. A rupture in a liquid pipeline is typically short and narrow, i.e. a slit or ‘fish-mouth’ opening. The decompression of liquid (or dense) phase carbon dioxide (CO2) immediately after a rupture is characterised by a rapid decompression through the liquid phase, and then a long plateau. At the same initial conditions (pressure and temperature), the initial speed of sound in dense phase CO2 is greater than that of natural gas and less than half that of water. Consequently, the initial decompression is more rapid than that of natural gas, but less rapid than that of water. A question then arises … Does a rupture in a liquid (or dense) phase CO2 pipeline behave like a rupture in a liquid pipeline or a gas pipeline? It may exhibit behaviour somewhere in-between the two. A ‘short’ defect that would rupture at the initial pressure might result in a short, narrow rupture (as in a liquid pipeline). A ‘long’ defect that would rupture at the (lower) saturation pressure might result in a long, wide rupture (as in a gas pipeline). This is important, because a rupture must be long and wide if it is to have the potential to transform into a running fracture. Three full-scale fracture propagation tests (albeit shorter tests than a typical full-scale test) published in the 1980s demonstrate that it is possible to initiate a running ductile fracture in a CO2 pipeline. However, these tests were on relatively small diameter, thin-wall line pipe with a (relatively) low toughness. The results are not applicable to large diameter, thick-wall line pipe with a high toughness. Therefore, in advance of its full-scale fracture propagation test using a dense phase CO2-rich mixture and 914×25.4 mm, Grade L450 line pipe, National Grid has conducted three ‘West Jefferson Tests’. The tests were designed to investigate if it was indeed possible to create a long, wide rupture in modern, high toughness line pipe steels using a dense phase CO2-rich mixture. Two tests were conducted with 100 mol.% CO2, and one with a CO2-rich binary mixture. Two of the ‘West Jefferson Tests’ resulted in short ruptures, similar to ruptures in liquid pipelines. One test resulted in a long, wide rupture, similar to a rupture in a gas pipeline. The three tests and the results are described. The reasons for the different behaviour observed in each test are explained. It is concluded that a long, wide rupture can be created in large diameter, thick-wall line pipe with a high toughness if the saturation pressure is high enough and the initial defect is long.

Pressure responses and phase transitions during the release of high pressure CO 2 from a large-scale pipeline

“…In order to develop accurate models for predicting the depressurization and phase transition behavior during CO 2 pipeline blowdown, several experimental research programs have been performed. Cosham et al [17] reported three West Jefferson Tests conducted on behalf of National Grid at the Spadeadam Test Site to investigate ductile fracture propagation in pipelines transporting liquid or dense phase CO 2 . The depressurization of liquid or dense phase CO 2 after a rupture was characterised by a rapid depressurization through the liquid phase, and then a long plateau.…”

Pressure response and phase transition in supercritical CO2 releases from a large-scale pipeline

“…The two factors that affect the appearance of a rupture are the length of the initial defect and the ratio of the toughness of the line pipe to the toughness required to arrest a 4 / 31 running ductile fracture. [18]. Koeijera et al [19] built a horizontal pipeline with a length of 139 m and an inner diameter of 10 mm in order to study the depressurization behavior of liquid CO .…”

Fracture propagation control in CO 2 pipelines: Validation of a coupled fluid–structure model

“…Recently, several research programmes have been initiated to prepare the industry for CCS and address the issue of FPC in CO 2 pipelines. The COOLTRANS project, run by National Grid (UK) has carried out and published results from five experiments connected to FPC in dense-phase CO 2 pipelines [11,36]. Two of these were full-scale crackarrest experiments with a CO 2 -N 2 mixture, and the conclusion was that the common method to address the FPC issue in pipelines, the Battelle Two Curve Method (BTCM) [20], 'is grossly non-conservative' [11] and 'not (currently) applicable to liquid or dense phase CO 2 or CO 2 -rich mixtures' [12].…”