Experimental study of decompression wave characteristics and steel pipe applicability of supercritical CO2 pipeline

High-strength pipeline steel is the optimal choice for continuously transporting large amounts of carbon dioxide (CO2) in the future Carbon capture, utilization and storage (CCUS) industrial chain, and supercritical CO2 (S-CO2) is the ideal phase state from an emitter to an onshore storage site. In CCUS projects, it is very indispensable to carry out the suitability of high steel-grade pipelines to ensure the safe operation of pipelines. It is considered a catastrophic incident for creatures and equipment once pipeline failure when fractures or propagation occurs. In this paper, the fracture propagation velocity of X70, X80, and X90 pipeline materials is calculated base on the high strength line pipe (HLP). Meanwhile, three sets of full-bore fracture (FBR) experiments of S-CO2 pipelines were conducted with similar initial status on an industrial-scale setup, and the decompression wave velocity was obtained with the data acquisition system. The result shows that the initial decompression wave velocity of S-CO2 is about 270 m/s, and the pressure plateau is between 6.8 and 7.3 MPa, corresponding to the decompression wave velocity, which is about in the range of 100-220 m/s. After that, the decompression wave velocity prediction model was established based on the homogeneous equilibrium method (HEM) and the equation of state (Eos), and the prediction results are more conservative than the experimental results. To ensure that the pipeline will not ductilely fracture in the event of a leakage or rupture, X70, X80 and X90 grade steel pipeline design wall thickness and minimum arrest toughness values are determined based on the two-curve method (TCM), respectively. Furthermore, a CO2 pipeline design model is developed based on the experimental data and decompression wave calculation method. The significant experimental data could be used for safety assessment and theoretical model validation in the CO2 transport pipeline and is useful in developing better fracture control models.