Experimental investigation on the stress of supercritical and dense-phase CO2 pipeline system in the venting process

Abstract

Releasing supercritical and dense-phase CO₂ from pipelines entails significant phase transitions and swift depressurization. This leads to significant temperature drops and reverse thrust forces, posing risks to pipeline integrity and support structures. This study investigates stress distribution across pipeline sections during vertical and horizontal releases of supercritical and dense-phase CO₂, aiming to quantify external thrust generated during discharge. Experiments were conducted at pressures ranging from 7.5 MPa to 10.0 MPa and temperatures between 25 °C and 40 °C. Maximum stress distribution across pipeline sections was measured, and a practical formula was developed to estimate external thrust during CO₂ discharge. The effects of impurities like N₂ and CH₄ on pipeline vibrations and stresses were also examined. Results indicate that maximum stress concentration occurs near the initial support point, mainly due to the excessive strength of a singular support structure. During CO₂ release, the pipeline system undergoes significant vibrations, leading to excessive longitudinal and hoop stresses. Impurities such as N₂ and CH₄ further exacerbate flow non-uniformity and vibration intensity. Notably, dense-phase CO₂ discharge generates higher maximum stress under identical conditions than supercritical CO₂ discharge. The reverse thrust formula demonstrates reasonable applicability under supercritical conditions. The findings emphasize the importance of considering phase behavior and impurity effects in pipeline safety assessments.