Chapter 12 - Drag Reducers

Abstract

This chapter deals with drag reduction in pipelines for liquid transportation. Pipeline flow improvers, or drag-reducing agents (DRAs), have been utilized in the petroleum industry for many years. They are important in oil drilling applications and the maintenance of pumping equipment in pipelines. It has been suggested that drag reduction occurs by the interaction between elastic macromolecules and macrostructures in turbulent flow. In turbulent pipe flow, the region near the wall, which is composed of a viscous sublayer and a buffer layer, plays a major role in drag reduction. The most serious problem in the effectiveness of drag reducers is the chain degradation of polymers by shear strains under conditions of turbulent flow. Ultra-high molecular weight polymers are more sensitive to shear-induced degradation, polymers with linear-chain structures are more vulnerable than branched polymers, and natural gums with semirigid structures. The mechanism of shear degradation is thought to be associated with chain elongation. Chain degradation is often observed when the shear rate is increased to a critical point, after which drag reduction decreases sharply. To address such drags there are various drag-reducing chemicals such as: ultra-high molecular weight polyethylene, copolymers of α-Olefins, latex drag reducers, polyether compounds for oil-based well drilling fluids, tylose, microencapsulated polymers, and aluminum carboxylate.