The plug formation in industrial pipelines is a critical problem, leading to emergency shutdowns, economic losses, and possible environmental pollution. It is most acute for oil and gas pipelines plugged by gas hydrates, which are sticky and cohesive particles. Understanding the mechanisms and patterns of blockages can help improve methods for their prevention.
Studying blockages often refer to straight horizontal pipes. In contrast, the zones of local narrowing, encountered in practice in the form of transitions between pipes, valves, and orifices, are not widely considered. This paper presents the results of studying the plug formation near an orifice in a turbulent oil-based "decan-ice particles" slurry flow. The study was carried out in a laboratory loop, in a 22-mm diameter pipe, at Reynolds numbers 4700 - 18400. It was found that blocking the orifice is possible at low concentrations of particles (2.2% vol.). This result is lower than the predictions of flow maps developed for similar systems. At the same time, an existing blockage evaluation technique could predict the boundaries of the loop flowability regimes.
A streamlining of the pipe geometry reduced the possibility of orifice blockage significantly. In some experiments, the minimal Reynolds number for a plug-free flow regime was decreased by 74%. It was done by removing the dead zones and branches in the pipes, which intensively accumulated the deposits of particles.