Post on 15-Dec-2015
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Process AuxiliariesAuxiliaries: 1. Pipe2. Pipe fittings3. Pipe supports4. Valves5. Measuring Instrument
Pipe: It is a tubular item made of metal, Plastic, Glass etc. meant for conveying any type of fluid. Piping is the physical elements that interconnect the equipment. Piping comes in different size and materials.
Pipe standards depends on Schedule Number and Nominal Pipe Diameter.1.) Schedule Number= (1000* Allowable Internal Pressure) / StressSchedule numbers uses 10, 20, 30, 40, 60, 80, 100, 120, 140 and 160. Among these 40 is standard value.2.) Nominal Pipe Diameter for 1/8 to 12 is equal to I.D while for greater than 12 its equal to O.D.
Diameter (in)= 3.9qf0.45raw0.13The wall thickness varies with the schedule number, nominal diameter which is independent of schedule number is constant which permits use of standard fittings and other tools. Design of Piping Layout:1) Choice of materials and Size: 2) Adequate Support3) Instrumentations4) Effect of temperature5) Easy Installation6) Maintenance and inspection 7) Safety
Figure.1 Piping LayoutIn the figure, p-100-18 presences the piping material and its size. The process piping layout shows the arrangement of the major pieces of equipment and their interconnection like condenser, pump, Distillation column, Reboiler. It is a description of the nature of the process. Details of the valves and fittings; and their arrangement.
Pipe Fittings: Pipe fittings are shapes which allow rigid straight pipe to change both direction and diameter.1.) Elbows: Elbows used to change the angle or direction of the pipe. Elbow have two angles 1) 45 2) 90.2.) T-fittings: Allow for branch lines. 3.) Couplings: Used to join two straight pieces of pipe of the same diameter. 4.) Reducers: Used to join pipe of different diameters5.) Bushings: Used to make the diameter of a pipe fitting smaller.6.) Adaptor: Used to change the end of a non-threaded pipe to male or female threads as needed. 7.) Unions: Used to join pieces of pipe where pipes cannot be turned or when a piece of equipment may have to be removed for maintenance or replacement.8.) Caps: Used to close the end of a dead end pipe.
Valve: Devices that control the flow of liquid or gas through a pipe.Mainly three types of valves:1.) On-Off Valve:a.) Gate Valve: Gate valves are primarily designed to serve as isolation valves. In service, these valves generally are either fully open or fully closed. A gate valve is operated with a wheel that moves a gate up and down. Gate valves have either rising stems, which enable you to tell visually if they are open or closed (although not as clearly as the lever on a ball valve). They should be used only in the fully open and fully closed positions. If a valve is left partially open, the gate will vibrate and may become damaged. Their ability to cut through liquids, gate valves are often used in the petroleum industry.
High CapacityPoor Control
Tight ShutoffProne to cavitation
No water hammeringCannot be used for throttling
Little resistance to flow
b.) Ball Valve: Ball valves are valued for their longevity and ability to work perfectly after years of disuse. Inside a ball valve, a sphere usually made of brass, chrome-plated brass, or stainless steel has been drilled through from one end to the other. Attached to the top of the sphere is a lever whose range of movement is just a quarter turn.
Advantage to quarter-turn valves such as ball valves is that they can be shut off quickly. Its much easier for persons of all abilities to move a lever than to turn a wheel in gate valve. Second, its possible at a glance to tell if a ball valve is open.The disadvantage is that this makes water hammer more likely. Required more space as compared to gate valve because shutting off the water flow means turning the lever perpendicular to the pipe, a ball valve may not work in certain tight locations. Ball valves are durable, performing well after many cycles, and reliable, closing securely even after long periods of disuse. These qualities make them an excellent choice for shutoff applications,
Water Hammering: Water hammer is a pressure wave caused when a fluid in motion is forced to stop or change direction suddenly. A water hammer commonly occurs when a valve closes suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe. It is also called hydraulic shock. Water hammering can cause pipelines to break if the pressure is high enough at downside of pipe.
Low costPoor throttling characteristics
High capacityProne to cavitation ( affect due to pressure difference between two side produce vapor and other reason is continuous contact with liquid for long period)
Low leakage and maintenanceWater hammering
Tight sealing with low torqueRequired more space
2.) Regulating Valvea.) Globe Valve: These valves are used in systems where good throttling characteristics and low seat leakage are desired and a relatively high head loss in an open valve is acceptable. they close slowly to prevent fluid hammer.Globe Valves
Efficient throttlingHigh pressure drop
Accurate flow control valvesMore expensive than other valves
Available in multiple ports
b.) Butterfly Valve: A butterfly valve is a valve which can be used for isolating or regulating flow. The closing mechanism takes the form of a disk. Operation is similar to that of a ball valve, which allows for quick shut off. Butterfly valves are generally favored because they are lower in cost to other valve designs as well as being lighter in weight, meaning less support is required. The disc is positioned in the center of the pipe, passing through the disc is a rod connected to an actuator on the outside of the valve. Rotating the actuator turns the disc either parallel or perpendicular to the flow. Unlike a ball valve, the disc is always present within the flow, therefore a pressure drop is always induced in the flow, regardless of valve position.Butterfly Valves
Low cost and maintenanceHigh torque required for control
High capacityAlways pressure drop
Good flow control
3.) Non-Return Valve:a.) Ball Check Valve: These are unidirectional valves and permit the free flow in one direction only. These valves have two ports: one for the entry of fluid and the other for the discharge. They are consists of a housing bore in which ball is held by a small spring force. The valve having ball as a closing member is known as ball check valve. The various types of check valves are available for a range of applications. These valves are generally small sized, simple in construction and inexpensive. Generally, the check valves are automatically operated.
The ball is held against the valve seat by a spring force. It can be observed from the figure that the fluid flow is not possible from the spring side but the fluid from opposite side can pass by lifting the ball against. However, there is some pressure drop across the valve due to restriction by the spring force. Therefore these valves are not suitable for the application of high flow rate. When the operating pressure increases the valve becomes more tightly seated in this design.
b.) Poppet check Valve: The advantages of the poppet valves include no leakage, long life and suitability with high pressure applications.
Instrumentation: Used for measure various parameters of fluid flowing to pipe like Temperature, Pressure, Flow.Flow measurement:1.) Orifice Meter: With an orifice plate, the fluid flow is measured through the difference in pressure from the upstream side to the downstream side of a partially obstructed pipe. The plate obstructing the flow offers a precisely measured obstruction that narrows the pipe and forces the flowing fluid to constrict. Most of the pressure drop is not recoverable, that is it is inefficient.
Types of Orifice PlatesThe simplest form of orifice plate consists of a thin metal sheet, having in it a square edged or a sharp edged or round edged circular hole.
There are three types of orifice plates namely1. Concentric2. Eccentric and3. Segmental type.
The concentric type is used for clean fluids. In metering dirty fluids, slurries and fluids containing solids, eccentric or segmental type is used in such a way that its lower edge coincides with the inside bottom of the pipe. This allows the solids to flow through without any obstruction.
Limitations: a.) Wear reduces the accuracy.b.) Water hammering damage orifice plate.
c.) Venturi Meter: It consists of a cylindrical inlet section equal to the pipe diameter ; a converging conical section in which the cross sectional area decreases causing the velocity to increase with a corresponding increase in the velocity head and a decrease in the pressure head ; a cylindrical throat section where the velocity is constant so that the decreased pressure head can be measured ; and a diverging recovery cone where the velocity decreases and almost all of the original pressure head is recovered.
C= dimensional coefficient, 0.935 to 0.988A2= Area of throat= D2/D1Sg= Specific GravityH= Height difference in manometerLimitations: This flow meter is limited to use on clean, non-corrosive liquids and gases, because it is difficult to clean out or flush out the pressure taps if they clog up with dirt or debris.
d.) Nozzle: The Flow nozzle is a smooth, convergent section that discharges the flow parallel to the axis of the downstream pipe. Thus the diameter ratio for a nozzle is smaller or its flow coefficient is larger. Pressure recovery is be