Preliminary Piping Design

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In Part 2 of our series on the Overview of Piping Design, we will examine the vital concepts used in developing an initial piping layout. See how the governing design principles including fluid properties, flow rate, and physical laws influence the complete piping system layout. Finally, understand how each of the different piping system components, such as tanks, vessels, valves, and pumps, impact the overall configuration.

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  • Fluid can be pushed down a pipe with a great deal of force. The only limit is the ability of the pipe to withstand the pressure. However, a liquid cannot be pulled up a pipe with much force because bubbles are created as the liquid evaporates into a gas. The greater the vacuum created, the larger the bubble, so no more liquid will flow into the pump. Rather than thinking in terms of the pump's ability to pull the fluid, the flow is limited by the ability of gravity and air pressure to push the fluid into the pump. The atmosphere pushes down on the fluid, and if the pump is below the tank, the weight of the fluid from gravity above the pump inlet also helps. Until the fluid reaches the pump, those are the only two forces providing the push. Friction loss and vapor pressure must also be considered. Friction loss limits the ability of gravity and air pressure to push the water toward the pump at high speed. Vapor pressure refers to the point at which bubbles form in the liquid. NPSH is a measure of how much spare pull you have before the bubbles form.
  • Since pump curves often are in head - feet or meters, its may be necessary with a conversion to the common pressure scales used in pressure gauges - psi or bar.Converting Head to PressureConverting head in feet to pressure in psiPump curves in feet of head can be converted to pressure - psi - by the expression:p = 0.434 h SG         (1)wherep = pressure (psi)h = head (ft)SG = specific gravityIn pumping this is particularly useful since we can get a handle on the characteristics of a pump by taking about the developed head of the pump. The developed head of a pump represents the height to which a fluid may be lifted by the pump in a frictionless piping system
  • E is the total energyM is mass flowrateJ is a conversion factorW is pump workgc is a conversion factor for the force of gravityg is acceleration due to gravityZ is the the elevationu is specific internal energy
  • There are three basic types of processes that piping is used for: These include high temperature, cryogenic and transmission.
  • Pipe sizes are determined by considering system demand, available fluid supply, and pipe network considerations such as friction loss, elevation changes, and pipe type.
  • Pipe sizes are determined by considering system demand, available fluid supply, and pipe network considerations such as friction loss, elevation changes, and pipe type.
  • Each of these types has several categories and designs, each offering different features and functional capabilities. Some valves are self-actuated while others are manually operated or have actuators that are powered with electric motors, are pneumatic or hydraulic, or a combination to operate the valve. The piping systems of industrial, commercial, residential, and other civic facilities carry the lifeblood of modern civilization, like arteries and veins. And the valves in those piping systems serve the functions of allowing, stopping, regulating, and controlling the flow, to fulfill the intended objectives of the system. When fluid pressure builds up beyond a set limit, the valves relieve the overpressure to safeguard the integrity of the piping system or a componentGlobe Valve is the most widely used type of control valve, has a screwed-on, integrally attached, or cage-supported seat ring, and typically a lathe-turned, single-seated valve plug.Angle valves are a special variety of globe valves typically havingan inlet port at a right angle to the valve stem and a discharge port in line with the valve orifice.Three-way valves are globe valves (or some rotary valves) that have three access ports and two plugs and orifices opposed to each other.Ball valves have a good shutoff characteristic and high flow capacity.Butterfly valves Except for some special designs with low-torque and low-noise features, butterfly valves for modulating control have to be selected with care.
  • Stop (Isolation) Valves - Gate, globe, ball, butterfly, plug, and diaphragm valves satisfy the above requirements in varying degrees and, therefore, are widely used in shut-off service.Regulating Valves are used extensively in piping systems to regulate the flow of fluid. Specially designed globe, needle, butterfly, ball, plug, and diaphragm valves are used in this serviceBackflow Prevention Valves used to prevent of backflow. The valves are self actuating and the valve disc is kept open by the forward flow of fluid.Pressure-relief Valve devices are used to protect piping and equipment from being subjected to pressures. The rupture disc is designed to burst open at a predetermined pressure.
  • a valve body subassembly (either with a reciprocating or rotating stem) an actuating device (usually a spring diaphragm type)a valve positioner (an instrument that converts an electronic control signal from a controller, or computer, into an air signal to control the position of the control valve stem)an airset or regulator to supply air pressure to the positioner
  • The piping of centrifugal pumps, particularly the suction piping, can seriously affect the operating efficiency and life expectancy of the pump. Poorly designed suction piping can result in the entrainment of air or vapor into the pump and cause cavitation, which displaces liquid from within the pump casing, results in vibrations, and throws the pump out of balance. The cavitation alone can result in severe erosion of the impeller. The out-of-balance condition may result in a slight eccentric shaft rotation, which will eventually wear out the pump bearings and seals, requiring a pump shutdown for overhaul.
  • A centrifugal pump moves fluid by rotating an impeller. The fluid enters the pump through the eye of the impellor, the fluid is accelerated outward from the pump casing. A vacuum is created at the impellors eye that continuously draws more fluid into the pump.A centrifugal pump converts the input power to kinetic energy in the liquid by accelerating the liquid by a revolving device - an impeller. The most common type is the volute pump. Fluid enters the pump through the eye of the impeller which rotates at high speed. The fluid is accelerated radially outward from the pump chasing. A vacuum is created at the impellers eye that continuously draws more fluid into the pump.
  • Pump Performance CurveThe pump characteristic is normally described graphically by the manufacturer as a pump performance curve. The pump curve describes the relation between flow rate and head for the actual pump. Other important information for proper pump selection is also included - efficiency curves, NPSHr curve, pump curves for several impeller diameters and different speeds, and power consumption. Increasing the impeller diameter or speed increases the head and flow rate capacity - and the pump curve moves upwards. The head capacity can be increased by connecting two or more pumps in series, or the flow rate capacity can be increased by connecting two or more pumps in parallel.
  • When routing piping at pumps, the designer should follow the manufacturer’s recommendations, the Hydraulic Institute Standards, and the following guidelines:
  • When routing piping at pumps, the designer should follow the manufacturer’s recommendations, the Hydraulic Institute Standards, and the following guidelines:
  • The loads transmitted from piping to shell nozzles of large-diameter tanks are a major concern for tank designers. We are going to cover some basics for piping design when attaching to different types of tanks and vessels.Tank: 26” Dia. Design Pressure: 50 psig; Capacity: 170 gallonsExamples: storage tank, drain tank, hot water expansion tank, glycol tankPressure Vessel: 48” Dia. 60” T-T; Capacity: 500 gallons, Design Pressure: 50 psig; Working Pressure: 178 psigExamples: reactor/process vessel, tower vessel, drum vessel
  • Stresses in the pipe caused by these load combinations should satisfy the ASME B31.3 Piping Code. Moment loads and resulting local stresses should also be checked in the tank nozzle and its connection to the tank, as covered by API Standard 650 for Atmospheric Storage Tanks.45
  • The loads transmitted from piping to shell nozzles of large-diameter tanks are a major concern for tank designers. We are going to cover some basics for piping design when attaching to different types of tanks and vessels.
  • for Atmospheric Storage Tanks.45Figure C7.19 provides some examples of typical piping configurations that deal with the load conditions. For most systems, there is an advantage in locating the first horizontal bend of the line as close as possible to the tank nozzle. This provides for tank shell nozzle rotation through torsion in the leg of horizontal piping after this first bend. Depending on the level of predicted tank settlement, which can approach 12 in (305 mm) or greater over the life of the tank, spring hangers may be required for the supports nearest to the tank.
  • Process unit feed tanks should have separate filling and discharge piping systems to avoid sending slugs of fluid to the process units. Separate discharge and suction connections are specifically required if it is necessary to have facilities for recirculation or blending and there is no mixer in the tank. Block valves should be provided on all nozzle connections below the tank liquid level. Filling lines for tanks containing flammable fluids should discharge near the bottom of the tank without free fall because of the danger of static electricity being created.
  • See picture in The piping handbook Fig. C7.16.
  • Connections off the bottom head of skirt supported vertical vessels should locate the nozzle flange outside of the skirt. This minimizes the possibility of flange leakage within the confined spaces of the vessel skirt. Flanged connections should be avoided on pressure vessels.
  • Preliminary Piping Design

    1. 1. Webinar Series: Overview of How Piping Design & AnalysisInfluences Pipe Support Selection & Design Preliminary Piping Design – Piping System Components Webinar Session # 2 July 18, 2012 By Piping Technology & Products
    2. 2. If you have any questions, comments orsuggestions, please email us atenews@pipingtech.comTo request a PDH certificate, email enews@pipingtech.com
    3. 3. PT&P Subsidiaries PIPING TECHNOLOGY & PRODUCTS, INC. Member of MSS, SPED, APFA, Fronek AnchorU.S. Bellows, Inc. Sweco Fab, Inc. Pipe Shields, Inc. Darling Ent., Inc.Member of EJMA ASME U-Stamp ISO 9001-2000 ASME Nuclear R-Stamp Certified Qualified
    4. 4. Webinar Series: Overview of How PipingDesign & Analysis Influences Pipe SupportSelection & DesignTopic Session / DateIntroduction I. Overview of Piping (completed)Preliminary I. Piping System II. The Total SystemPiping Design Components July 25, 2012 July 18, 2012Basic Concepts I. Part 1 II. Part 2of Stress August 1, 2012 August 8, 2012AnalysisInfluences on I. Rigid Supports II. Spring Supports III. RestraintsPipe Support August 15, 2012 August 22, 2012 August 29, 2012Design
    5. 5. Presentation Outline Introduction ◦ Total System (Brief Overview) ◦ Fluid Properties ◦ Terminology Piping & Fittings Valves Centrifugal Pumps Tanks and Vessels
    6. 6. Introduction Design Basis The first step in design is determining the design bases to be used in the system. Pressure integrity is the maintenance of a leak-tight condition in piping systems’ pressure-containing boundaries coincident with the control of the level of stress or strain within predefined criteria limits. Proper planning is an important activity performed by the Piping Designer in the early stages of the project. The design basis which must be considered include: ◦ physical attributes ◦ loading and service conditions ◦ environmental factors ◦ materials-related factors
    7. 7. Introduction The Total System Physical attributes are those parameters that govern the size, layout, and dimensional limits or proportions of the piping system. Loading conditions, or loads, are forces, moments, pressure changes, temperature changes, thermal gradients, or any other parameters that affect the state of stress of the piping system.
    8. 8. Introduction The Total System Environmental factors refers to operating conditions that result in progressive physical or chemically induced deterioration of the piping system which can ultimately lead to a breach of the pressure boundary or a gross structural failure. Materials-related considerations are the specific chemical, metallurgical, and physical properties of a piping system’s material constituents that can ultimately determine its suitability for a particular service.
    9. 9. Introduction Fluid Properties  The material in the pipe can be a gas, liquid or vapor. Vapors can be considered fluids.  Gas is a fluid that expands to fill any vessel in which it is contained, is easily compressed, and any change in pressure is accompanied by a change in volume and density.  Liquids change volume and density very slightly in response to changes in pressure.  Hydrostatic Pressure – The static pressure existing at a point within a fluid bodySource: Research the Topic – Wikispaces.com
    10. 10. Introduction Fluid Properties Terminology The following symbols are used in this section in defining the interrelation of work, power, and energy:  A area, in2 or ft2 (mm2 or m2) as noted  F force, lbf (newton, N)  g local acceleration of gravity, ft/s2 (9 · 81 m/s2)  gc conversion constant, ft · lbf/(lbm · s2) [m· kgf/(kgm · s2)]  h vertical distance, ft (m)  H enthalpy, Btu (gram · cal)  hp horsepower (J/s, kW)  kW kilowatts  KE kinetic energy, ft · lbf (m · kgf)  PE potential energy, ft · lbf (m · kgf)  p pressure, psi (kPa, kg/cm2)  l distance, ft (m)  T time, s  v velocity, ft/s (m/s)  V volume, ft3 (m3)  w weight, lb (kg)  W work, ft · lb (m· kg)Image Source: dinomiteseo.com
    11. 11. Introduction Fluid Properties Terminology Simple forces - When two or more forces act upon a body at one point, they may be single or combined into a resultant force Moments - The moment of a force with respect to a given point is the tendency of that force to produce rotation around it. Moments acting in a clockwise direction are designated as positive, and those acting in a counterclockwise direction are negative. Couples - Two parallel forces of equal magnitude acting in opposite directions constitute a couple.
    12. 12. Introduction Fluid Properties Terminology Flow Rate – as mass flow rate or volumetric flow rate. Pressure – in terms of piping is monitored to prevent state change, and to determine overall fluid velocity. Pressure losses – occur in piping systems due to bends, elbows, joints, valves , and so forth are called form losses
    13. 13. Introduction Fluid Properties Terminology  Head – amount of mechanical energy per unit weight.  Head loss – is the energy loss due to friction • Net fluid in the pipe. between the pipe and thePositive Suction Head – the net (left over) positive pressure of suction force into a pump intake after friction loss has occurred. Liquid head height or liquid head pressure + gravity pressure, minus friction loss, leaves a netImage Source: chestofbooks.com head pressure of force into
    14. 14. Introduction Fluid Properties Terminology Law of Equilibrium – When a body is at rest, the external forces acting upon it must be in equilibrium and there must be a zero net moment on the body. Viscosity – The resistance of a fluid to shear stress. Reynolds Number – A dimensionless number. It is defined as the ratio of the dynamic forces of mass flow to the shear stress due to viscosity.
    15. 15. Introduction Fluid Properties Terminology
    16. 16. Introduction Fluid Properties Applying the law of conservation to a flow process yields a mass balance. The mass of the fluid added to the system is equal to the mass subtracted from the system plus any fluid accumulated by the system. Energy acts as defined by the first law of thermodynamics.
    17. 17. Introduction Fluid Properties: Physical Laws that Govern Fluid FlowThe energy it takes to transport the material through the system consists ofpotential (external), kinetic, and internal energy of the fluid, and also the externalpumping work, the energy transmitted by a pump to force the fluid to flowcontinuously across the boundary of the system.For pipes or ducts this can be expressed as:
    18. 18. Introduction Fluid Properties: Physical Laws that Govern Fluid Flow Designers must accurately calculate the amount of work required to transport a fluid inside a pipe Work consists of using pumps, compress ors or gravity to move material from one location to another
    19. 19. Piping SystemComponents Main Types of Processes High temperature process – steam lines, heat transfer fluids, and hot oils. Cryogenic processes – liquefied natural gas, polyethylene, and other liquefied gas processes.• Transmission – sewage service, water lines, natural gas lines, hydrocarbon lines.
    20. 20. Piping and Fittings Characteristics Piping and fittings are specified based on their nominal size, schedule, and materials of construction. Load / pressure capacity is a function of the physical attributes of the piping used and the operating temperature. Allowable stress levels will be specified in the applicable code or standard. Pressure vessels piping is usually defined by ASME Section VIII which includes piping between the vessels protected by the same relief valve, and piping between a vessel and its pressure relief safety valve.
    21. 21. Piping and Fittings Pipe Sizing and Selection Source: Mohinder L. Nayyar, “Piping Handbook”
    22. 22. Piping and Fittings Pipe Sizing and Selection  Selection of pipe thickness would be dependent upon the same parameters utilized in the pipe sizing selection criteria.  Two of the most widely accepted design formulas: ◦ 1.) ◦ 2.) Where t = design minimum wall thickness required to ensure pressure integrity, in P = design pressure, psig D = outside diameter of pipe, in S = allowable stress, psig E = weld joint efficiency factor (some codes also specify a casting quality factor F for casting piping materials) y = dimensionless factor which varies with temperatureSource: Mohinder L. Nayyar, “Piping Handbook”
    23. 23. Piping and Fittings Head Loss Calculations  Piping Head loss can be calculated using a number of calculations depending the type of piping and the attached equipment.  The equations used are: Darcy-Weisbach where and and Fanning where and and Hazen-Williams In In M FtSource: Mohinder L. Nayyar, “Piping Handbook”
    24. 24. Piping and Fittings Head Loss Calculations
    25. 25. Piping and Fittings Piping Considerations Head loss can be affected by: ◦ Pipe Diameter: objective is to balance the pipe diameter versus the overall cost.  Remember that a decrease in pipe diameter would mandate and increase in flow velocity and more pressure loss.  Conversely an increase in pipe diameter would result in a lower pump capacity requirement, but increase piping material cost.  Roughness of Pipe: decreasing the roughness of the pipe would result in a smoother flow with less turbulence.  Piping Configuration: reduction in the overall length, directional changes, and diameter variations will decrease cost.  Viscosity of Fluid: higher viscosity fluid requires more powerful pumping of the fluid and supporting of the pipe.
    26. 26. Valves Valves are an essential part of any piping system that conveys liquids, gases, vapors, slurries and mixtures of liquid, and gaseous phases of various flow media. Different types ◦ Diaphragm of valves include: ◦ Gate ◦ Pinch ◦ Globe ◦ Pressure ◦ Check ◦ Relief ◦ Ball ◦ Control ◦ Plug ◦ Butterfly
    27. 27. Valves Functions Stop (Isolation) Valves ◦ i.e. gate, globe, ball, butterfly, plug, diaphragm Regulating Valves ◦ i.e. globe, needle, butterfly, ball, plug, diaphragm Backflow Prevention Valves Pressure-relief Valve
    28. 28. Valves Operation Valve Components: ◦ Valve body subassembly ◦ Actuating device ◦ Valve positioner ◦ Airset or regulatorSource: Navy Firefighter, Fireman Training
    29. 29. Control Valves Sizing and Selecting Control Valves The flow capacity of control valves is expressed by the coefficient Cv. This is a combination of valve flow area and the valve’s head loss coefficient K.• Normal Flow This occurs when the pressure drop across the valve lies below the following equation limits. Where plim is the limited pressure drop across the valve (see equations), p1 is the valve’s inlet pressure, and pv is the vapor pressure of the respective fluid and at the flowing temperature (all pressures absolute).Choked Flow This occurs if the actual pressure drop exceeds plim.CAUTION: Such conditions could cause cavitation in valves handlingliquids.
    30. 30. Control Valves Control Valves Equations FOR LIQUID SERVICE Volumetric Flow Flow by WeightSource: Mohinder L. Nayyar, “Piping Handbook”
    31. 31. Control Valves Control Valves Equations FOR GAS AND STEAM SERVICE Volumetric Flow Flow by WeightSource: Mohinder L. Nayyar, “Piping Handbook”
    32. 32. Control Valves Control Valves Equations For Saturated Steam For Superheated Steam
    33. 33. Centrifugal Pumps Typical Pump  Major Pump Parts Application  Theory of Operation  Understanding the Pump Curve  Pump Power & Cost Operation  Net Positive Suction Head and Cavitation  Piping ConsiderationsSource: Mohinder L. Nayyar, “Piping Handbook”
    34. 34. Centrifugal Pumps Theory of Operation  Uses Rotating Impeller  Fluid Enters at Eye  Accelerated by Impeller  Vacuum is Generated  Continuous Fluid FlowSource: Basic Chemical Engineering Operations (engineeringoperations.blogspot.com)
    35. 35. Centrifugal PumpsPump Head: Measure of fluid energy. It is used todescribe the specific energy of a pump.Types of Pump Head Dynamic Suction Head/Lift - Head on suction side of pump with pump on Dynamic Discharge Head - Head on discharge side of pump with pump on Total Dynamic Head - Total head when the pump is running Static Suction Head - Head on the suction side, with pump off, if the head is higher than the pump impeller Static Suction Lift - Head on the suction side, with pump off, if the head is lower than the pump impeller Static Discharge Head - Head on discharge side of pump with the pump off Total Static Head - Total head when the pump is not running
    36. 36. Centrifugal Pumps Pump Curve Provides Details Of:  Pump Efficiency  NPSH  Various Impeller Diameters  Pump Power Consumption Example published pump performance curve Note: All pumps must operate at a NPSH to prevent cavitation. Using the pump performance curve, the required NPSH for safe operation is given.Source: Pumps & Systems (pump-zone.com)
    37. 37. Centrifugal Pumps Application Guidelines  Location of flat when using eccentric reducers  All pump suction lines must be designed to accommodate a conical-type temporary strainer.  The suction of any centrifugal pump must be continuously flooded, and the suction piping shall contain no vertical loops or air pockets.Source: Pumps & Systems (pump-zone.com)
    38. 38. Centrifugal Pumps Application Guidelines  The suction and discharge piping must be supported independently of the pump such that very little load is transmitted to the pump casing. The designer may consider the use of expansion joints on either the suction or discharge, or both, as necessary. However, expansion joints should be used only when it is unavoidable.  A pipe anchor must be provided between any expansion joint or non-rigid coupling and the pump nozzle that it is designed to protect.  Only long-radius elbows are to be used at or adjacent to any pump suction connection.Source: Pumps & Systems (pump-zone.com)
    39. 39. Tanks and Pressure Vessels Tanks vs. Pressure Vessels ◦ Tanks: A storage device meant to hold fluid media, either liquid or gas. Pressure developed is a function of the tank size and not a result of any external forces. ◦ Pressure Vessels: A storage device meant to hold fluid media while simultaneously containing reactions at Pressure Tank pressures above atmospheric Vessel pressure.
    40. 40. Tanks and Pressure Vessels Tanks: Design Considerations The loads which must be considered in the design of principal piping connections to tank nozzles include the following: ◦ Tank shell radial movements and nozzle rotations while filling and emptying a tank ◦ Design pressure of the pipe ◦ Thermal expansion of piping ◦ Differential settlement between the tank and the piping supports ◦ Weight of piping, valves, and contents
    41. 41. Tanks and Pressure Vessels Tanks: Design Considerations 1 2 Determination of Nozzle Pressure Discharge velocity then becomes a function of the static pressures at positions P1 and P2, the fluid density andSource: Mohinder L. Nayyar, “Piping Handbook” the height of the tank (z).
    42. 42. Tanks and Pressure Vessels Tanks: Design ConsiderationsSource: Mohinder L. Nayyar, “Piping Handbook”
    43. 43. Tanks and Pressure Vessels Tanks: Application Guidelines For tanks that are feed tanks have separate feed and discharge systems. Block Valves should be supplied on any nozzles below the tank level. Flammable liquids in storage tanks should be filled near the bottom of the tank to prevent static electricity buildup.
    44. 44. Tanks and Pressure Vessels Pressure Vessels: Design Considerations Vessel specifications will be determined by the process engineer. (i.e. size/capacity, pressure rating, wall thickness, material, type of connection, etc.) Nozzle location will be controlled by the vessel designer. Piping should drop or rise immediately upon leaving the tower nozzle and run parallel along the side of the vessel using the wind load on the nozzle as constraint. It is also important to take the thermal expansion into account between the vessel shell and the
    45. 45. Tanks and Pressure Vessels Pressure Vessels: Design Considerations Most pipe supports will be attached to the side of the vessel. For connections to the bottom head of skirt supported vessel, the flanged connections should be outside of the skirt to minimize leakage in confined space. Isolation valves are usually provided if the location of the nozzle is below the column level or on small bore lines which are more susceptible to damage.
    46. 46. Next Webinar Session: July 25, 2012 Session 3: Preliminary Piping Design – The Total System Continuing our series on the Overview of Piping Design, Part 3 will take a detailed look at the total piping system. Understand the different types of equipment and components that define various types of piping systems. Familiarize yourself with key piping system concepts and how to calculate flow between two pressure sources. Learn the differences between series piping, parallel piping and branch piping as well as their specialized applications. See how the piping system conditions such as static and dynamic head loss influence the selection and distribution of piping components throughout the entire system. Finally, eliminate potential danger areas using our piping system trouble shooting guide. If you have any questions, comments or suggestions, please email us at enews@pipingtech.com To request a PDH certificate, email enews@pipingtech.com

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