Piping [Lesson 1A]

Module Objectives
At the completion of this module, you will be able to:
- Describe piping and piping systems.
- Describe the basic components of piping systems.
- Describe how piping works.
- Describe the guidelines for operating piping systems.
- Describe how to maintain piping systems.

Module Introduction
Piping is a network or system of pipes, valves, and auxiliary equipment that channels fluids (liquids, gases, or fluidized solids) between plant vessels and equipment. As an operator, you must understand how piping affects process conditions. Piping obstructions and failures can affect operating safety and efficiency and be detrimental to product quality. In this module you will learn about piping and piping systems. You will also learn how to operate and perform preventive maintenance on piping systems.

Lesson 1 — ABOUT PIPING
Lesson Objectives
In order to complete this lesson, you must:
- Define fluid, pressure, and viscosity.
- Describe the three major functions of piping.
- Describe how piping, fittings, and valves are sized and rated.
- Describe how piping is installed

Lesson Introduction Piping systems are the conduits used to efficiently carry process fluids throughout a process plant. Understanding the basic concepts of piping systems will help you become a qualified, efficient, and safe operator.

In your work as a plant operator, you will use the basic concepts of piping every day. Understanding piping principles and functions will also aid you in your study of other operator training lessons.
In this lesson you will learn the basics of fluids, pressure, and viscosity, as well as piping functions, construction, and installation.


Fluids, Pressure, and Viscosity
In a process facility, piping directs the flow of fluids between the various vessels and equipment. To understand piping and its functions, you need to first understand fluids and the forces that act upon them.


Fluids Defined A fluid is any substance that flows. This, essentially, includes all substances that are not large undivided solids. Liquids, gases, and finely divided fluidized solids are all fluids. For the purposes of this module, fluids are able to flow through an enclosed piping system.


Definition of a Liquid A liquid is a fluid that flows freely but does not have a tendency to separate. Water is a good example. Internal forces hold a liquid together in a cohesive mass, while allowing it to flow and assume the shape of its container. A liquid does not appreciably change its volume when it is exposed to pressure variations.

Definition of a Gas A gas is an uncohesive fluid that expands to completely fill its container, and it has no independent shape or volume. Gases are compressible and can expand indefinitely. Gases have a proportional relationship between their quantity, volume , pressure, and temperature. If any one of these four variables change, a proportional change must occur in one or more of the other factors.

Definition of a Fluidized Solid A finely divided solid can be made to behave as a fluid if the mass of particles is aerated. Aeration is intermixing air, steam, or other gases into a bed of small solid particles so that the particles become separated and “lubricated.” While the aeration is maintained, the aerated mass can flow through piping, valves, and fittings as if it were a liquid. An example of a fluidized solid is the circulating catalyst in a Fluid Catalytic Cracking Unit

Pressure
Pressure is the force that a fluid exerts against the walls of the piping that contains it. Pressure is also the force that causes the fluid to move through the piping.


Pressure Defined Pressure is defined as a force per unit area. In the English measurement system, pressure is most often expressed as psi (pounds per square inch). This relates to the force, in pounds, that exerts itself against any square inch of area. Pressure exerts itself equally in all directions throughout any body of fluid. However, the weight of a fluid above any prescribed depth adds to the pressure at that level. This means that pressure increases with fluid depth.

Fluid Flow and Pressure Difference
Pressure Difference (dP) Pressure is the driving force to move a fluid in a piping system. To be more exact, fluid flow requires that a difference in pressure be established across the length of the pipe. The pressure must be greater at the upstream end of the pipe than at the downstream end. Pressure difference is often written as dP, d/P, or D P

NOTE
To move any fluid through a pipe, dP must be created across the pipe’s length. Either increase the upstream pressure, or decrease the downstream pressure, or both. As an example, a pump is a device that is used to increase the upstream pressure, creating dP and causing the fluid to flow.

Fluid Friction
Just as dP causes a fluid to flow, fluid friction opposes fluid flow. In any piping system, fluid friction increases with the rate of flow. When the flow begins for a given dP, flow increases until fluid friction balances the driving force. At that point, the rate of flow stops increasing and becomes constant.

NOTE
Fluid friction opposes fluid flow. Friction always increases as the flow rate increases. Therefore, for any given dP across a section of pipe, there is a steady maximum flow that results if no further restrictions are added.

Viscosity

There are two kinds of friction within any piping system:
- Wall friction between the fluid and the pipe walls
- Internal friction (or viscosity)

Viscosity, or the internal friction of a fluid, produces the greater resistance to flow. Fluids move through pipes in layers that slip by each other at different rates of flow. This shearing action creates friction. Viscosity increases with the “thickness” of the fluid. A thicker fluid has a higher viscosity (or resistance to flow).

In the pipe shown in Figure 1-1, the fluid is made to change direction with an ell-shaped fitting. In this case, the fluid turns 90° by friction with the wall of the ell. In the pipe on the right, a tee-shaped fitting is installed, and one side of the tee is plugged. Because the “dead” side of the tee is filled with fluid, the flow changes direction with friction against the “dead” fluid.

In this example the fluid friction in the tee is over nine times greater than it is in the ell, for the same flow rate. The greater friction is created by the viscosity of the fluid (or the fluid’s internal resistance to flow).

The Functions of Piping

Piping performs three major functions in the handling of fluids.

Functions The three major functions that piping performs are:
- Transporting fluids
- Containing fluid pressure
- Directing fluid flow and regulating flow rate

Transporting Fluids Piping is the conduit that contains and transports fluids throughout a processing plant. Piping can be branched to direct a fluid to several destinations simultaneously. It is the highway in which process fluids travel to reach vessels, heat exchangers, reactors, tanks, and other equipment within a process plant.

Containing Fluid Pressure Pressure is an important tool in a process. It is the energy used to move fluids through a process. It is able to concentrate a quantity of gas. And it assists chemical reactions in performing their transformations.

Piping can be designed to safely transport fluids that place extreme adverse conditions on the system. High pressure, high temperature, and corrosive fluids may be handled safely when proper design and metallurgy are used. The strength of the pipe wall determines if it can safely contain fluids under pressure.

Directing Fluid Flow and Regulating Flow Rate

As a fluid moves in a piping system, the flow may need to be manipulated. At times the flow needs to be:
- Stopped and isolated
- Regulated for rate of flow
- Routed through different piping
- Directed to a different destination

All of these operations are accomplished with valves. A valve is a special fitting with a moveable plug or gate in the flow path. When the valve is operated, the plug or gate stops or restricts the flow of fluid.