Overview

Fluid flow through pipelines is a complex and not completely understood problem. It is the subject of continuing research by engineers, physicists, and, more recently, those studying nonlinear dynamic systems, popularly called the science of chaos. In a relative risk assessment, we are less concerned with exact numerical solutions, and more interested in comparative values.

In general, fluid flow in pipes is assigned to one of two flow regimes, turbulent or laminar. Some make distinctions between rough turbulent and smooth turbulent, and a region termed the transition zone is also recognized. However, in simplest terms, the flow pattern will be characterized by uniform, parallel velocities of fluid particles laminar flow or by turbulent eddies and circular patterns of fluid particle velocities turbulent flow or by some pattern that is a combination of the two. The flow pattern is dependent on the fluid average velocity, the fluid kinematic viscosity, the pipe diameter, and the roughness of the inside wall of the pipe.

Several formulas that relate these parameters to fluid density and pressure drop offer approximate solutions for each flow regime. These formulas make a distinction between compressible and non-compressible fluids. Liquids such as crude oil, gasoline, and water are considered to be non-compressible, whereas gases such as methane, nitrogen, and oxygen are considered to be compressible. Highly volatile products such as ethylene, propane, and propylene are generally transported as dense gases they are compressed in the pipeline until their properties resemble those of a liquid, but will immediately return to a gaseous state on...