Impact of slug length in gas–liquid two-phase flow on the structural stress characteristics of horizontal rigid pipelines

The intermittent passage of liquid slugs and gas pockets in slug flow generates substantial cyclic stress damage to piping systems and their supports. This issue poses significant challenges to the various industries in which this flow pattern is present. Despite their critical implications, the structural response to slug-induced forces has not yet been thoroughly elucidated. This study addresses this gap through a comprehensive experimental investigation of the influence of slug length on the structural integrity of pipes. A non-invasive image-processing technique was employed to measure the slug length, while biaxial strain gauges captured the pipe wall strain, accounting for Poisson and friction fluid–structure interaction (FSI) coupling mechanisms. The findings revealed a reduction in the induced stresses with increasing superficial liquid velocity and slug length. Furthermore, a semi-empirical model was developed by integrating slug length with the superficial gas and liquid velocities based on the slug unit concept to predict the structural stresses. The model provides a robust predictive framework for elucidating the relationship between slug length and induced stresses. However, its accuracy is influenced by the slug formation mechanism and various slug flow sub-regimes. The model demonstrated exceptional predictive capability, achieving a mean error of 6.2% and coefficient of determination of 93%.