Principles of Liquid Flow through Pipelines Book 2: Chapter 3 Principles of Liquid Flow through Pipelines

Objectives After reading the chapter and reviewing the materials presented the students will be able to: Understand properties and characteristics of liquids Identify laminar and turbulent flow Describe solubility Explain mechanics of liquid flow Classify static pressure or head Examine atmospheric pressure

Introduction The principles governing the flow of fluids are based on application of the natural laws governing flow of fluids. The characteristics and properties of the pipeline affect the flow of liquids through them and must be considered. The large body of available knowledge regarding the flow of water through pipes was utilized and modified as needed in solving problems pertaining to the flow of crude oil and other liquids. There has been a parallel study of principles governing the flow of gases through pipelines.

Physical States Most materials can exist in three physical states: solids, liquids, and gas. The liquid state is more suitable for pipeline transportation than the gaseous state. Most solid material must be suspended or dissolved in a liquid or gaseous fluid to be transported in a pipeline. Transportation of liquefied petroleum gases (LPG) has become a large proportion of the petroleum industry.

Properties and Characteristics of Liquids 1. Fluidity: Both liquids and gases are fluids. Neither liquids nor gases have definite shapes and take the shape of the vessel containing them. It is the property of fluidity that makes pipeline transport possible. 2. Viscosity: Viscosity is a measure of the resistance of a fluid to motion. This resistance to flow is called fluid friction. The viscosity of liquids decreases with increasing temperatures. The viscosity of gases increases with increasing temperatures. Additional resistance to flow is caused by changes in pipe size, sharp bends, and deposits of rust or sediment in a pipe.

Properties and Characteristics of Liquids 3. Laminar and Turbulent Flow: Liquid velocity is near zero at the pipe wall and increases to maximum at the pipe center. This is called laminar flow. As liquid velocity increases, the liquid motion becomes more turbulent. At higher velocities the liquid particles all flow forward at about the same velocity at all points in the pipe. Flow in most crude oil trunk pipelines is turbulent. There is less tendency for waxy deposits to form on the pipe walls and water and sediment rarely separate from the oil to interfere with oil flow.

Properties and Characteristics of Liquids 4. Gravity: Flow of liquids through pipelines is affected by gravity. The magnitude of force depends on the weight of the liquid. Heavier liquids in motion have more kinetic energy. 5. Temperature: Fluidity within liquids increases with temperature. Proper design and operation of a pipeline requires knowledge of temperatures during flow and the effects of these temperatures. A liquid may be heated to improve flow characteristics. Operators of gas pipelines have had problems caused by the heat of gas compression. This heat must be removed from the compressed gas by the use of heat exchangers or allowed to dissipate from the pipeline.

Properties and Characteristics of Liquids 6. Solubility: Most of the cooling from formation temperatures occurs in the producer’s lease tanks or other facilities. During cooling, some of the wax, asphalt, and water comes out of the solution and tends to settle with the brine to the bottom of the containing vessel. The settlings are commonly called basic sediment and water (BS&W). Heat, chemical agents, and electrostatic precipitators are often used to hasten the process. Even after treatment some crude oils tend to deposit wax, hard paraffin, or asphalt materials on the walls of the pipe. These deposits impede flow by decreasing the pipe diameter. Provisions must be made for periodic scraping of the pipe walls. The most effective method of preventing internal corrosion is to operate the pipeline so that it is in turbulent flow. The turbulent flow keeps the brine suspended and effectively prevents corrosion.

Mechanics of Liquid Flow 1. Static Pressure or Head: Static pressure indicates that the liquid is at rest. The pressure is proportional to the depth below the liquid surface, and how much of the liquid is overhead. It is often called static head or simply head. Mixtures of oil and water can be separated by permitting the heavier water to seek its level at the bottom of the container.

Mechanics of Liquid Flow 2. Atmospheric and Atmospheric Pressure: The static head caused by the weight of the atmosphere is called atmospheric pressure. At sea level and a temperature of 320F this pressure is 14.7 psi. At high elevations there is less weight of air overhead, and atmospheric pressures are lower. Air expands and becomes lighter at higher temperatures so that it has less weight and pressure.

Mechanics of Liquid Flow 3. Dynamic Pressure: Dynamic head may result from energy supplied by a pump whereby pressure is raised from a lower to a higher value. Elevations of supply and delivery points cannot be changed appreciably, but the head available can be readily modified by adding pump pressure. Flow rates can be changed by changing pipe sizes and by changing pressures or heads used to cause flow. Hydraulic engineers would like to design pipeline systems that would carry the required volumes of liquids with expenditure of the least amount of energy.

Summary The liquid state is more suitable for pipeline transportation than the gaseous state. Most solid material must be suspended or dissolved in a liquid or gaseous fluid to be transported in a pipeline. Transportation of liquefied petroleum gases (LPG) has become a large proportion of the petroleum industry. Fluidity: It is the property of fluidity that makes pipeline transport possible. Viscosity: Viscosity is a measure of the resistance of a fluid to motion. The viscosity of liquids decreases with increasing temperatures. The viscosity of gases increases with increasing temperatures. Liquid velocity is near zero at the pipe wall and increases to maximum at the pipe center. Laminar and Turbulent Flow: Liquid velocity is near zero at the pipe wall and increases to maximum at the pipe center. This is called laminar flow. As liquid velocity increases, the liquid motion becomes more turbulent. At higher velocities the liquid particles all flow forward at about the same velocity at all points in the pipe. Gravity: Flow of liquids through pipelines is affected by gravity. Temperature: Fluidity within liquids increases with temperature. Solubility: During cooling, some of the wax, asphalt, and water comes out of the solution and tends to settle with the brine to the bottom of the containing vessel. The settlings are commonly called basic sediment and water (BS&W). The most effective method of preventing internal corrosion is to operate the pipeline so that it is in turbulent flow. The turbulent flow keeps the brine suspended and effectively prevents corrosion. Static pressure indicates that the liquid is at rest. The pressure is proportional to the depth below the liquid surface, and how much of the liquid is overhead. It is often called static head or simply head. The static head caused by the weight of the atmosphere is called atmospheric pressure. Dynamic head may result from energy supplied by a pump whereby pressure is raised from a lower to a higher value.

Home Work 1. How are solids transported in a pipeline? 2. Explain laminar and turbulent flow in a pipeline. 3. What is the most effective method of preventing internal corrosion in the pipeline ?