Presentation on theme: "CM4120 Unit Operations Lab Piping Systems"— Presentation transcript:
1CM4120 Unit Operations Lab Piping Systems Piping Systems in the Chemical Process IndustriesMarch, 2009IntroductionBasis for DesignPiping Codes and StandardsDesign of Process Piping SystemsJoints and FittingsValves
2CM4120 Unit Operations Lab Piping Systems Piping Systems include:Pipe, Flanges, FittingsBolting, GasketsValvesHangers and SupportsInsulations, Coverings, CoatingsHeat TracingEverything between equipment and instrumentation is considered piping
3CM4120 Unit Operations Lab Piping Systems “Piping systems are like arteries and veins. They carry the lifeblood of modern civilization.”Mohinder Nayyar, P.E.Piping Handbook, 7th ed.McGraw-Hill, 2000The invention of piping systems is what allowed civilization to develop beyond small villages.Early records show use of hollow log piping and open-channel water distribution systems by the Egyptians, Romans, and Babylonians.
4CM4120 Unit Operations Lab Piping Systems Primary Design Consideration is SafetyEvaluate Process ConditionsTemperaturePressureChemical compatibility/Corrosion allowancesVibration, flexing, bendingExpansion/Contraction due to temperature changeEnvironmental conditionsEvaluate the Effects of a LeakEvaluate Performance in a Fire SituationBefore starting to design a piping system there are many considerations.Foremost concern in any good design is safety.
5CM4120 Unit Operations Lab Piping Systems Secondary ConsiderationsEvaluate any Special RequirementsSanitary requirements – “Cleanability”Serviceability – ease of maintenance of equipmentPossible contamination of process fluid by piping materials, sealants, or gasketingEarthquake, Hurricane, Lightening, PermafrostLowest Cost over the LifetimeDoes the system have to be disassembled frequently for maintenance or cleaning?Are there trace elements in the piping, sealants, or gasketing that may contaminate the process fluid or utility?What is the total cost of the piping system over the expected life?
6CM4120 Unit Operations Lab Piping Systems Piping System Routing and LayoutThe unwritten #1 rule:Serviceability/OperabilityUO Lab
7CM4120 Unit Operations Lab Piping Systems Piping System Design Criteria4 areas to consider:Physical AttributesLoading and Service ConditionsEnvironmental FactorsMaterials-Related ConsiderationsPhysical Attributes:SizeLayoutDimensional limitsOperability (slope for drainage, mechanical fittings for ease of dis-assemblyLoading/Service Conditions:conditions that stress the piping system- internal – from process fluids – pressure, temperature, T/P cycling- external – from wind, ice, service personnel, trafficalso consider load cycling and load durationmust design for all expected combinations/ worst caseEnvironmental Factors:physical and chemical conditions that deteriorate the system over time- corrosion (internal or external)- erosion- physical damage – fork lift operatorsMaterials-Related Considerations:Strength – something like 2/3 of yield strengthToughness- use ductile materials, CS is ductile down to T = 0 F, then reduce P ratingCorrosion resistance– negligible over design lifetime, increase wall thickness if necessary- use design temp to determine corrosion rate- will corrosion create process fluid contamination problem?- Special considerations – CS is subject to Graphitization when T>775 Ffor long periods (carbon converts to graphite and becomes brittle)Pressure integrity – Leak-tight WRT stress/strain in pipe system (not gaskets or seals)
8CM4120 Unit Operations Lab Piping Systems Codes and Standards simplify design, manufacturing, installation processStandards – provide design criteria for componentsstandard sizes for pipedimensions for fittings or valvesCodes – specific design/fabrication methodologiesIncorporated into local/regional statuteIt’s the LAWUse commonly accepted methods-- reduce design time-- produce safe design-- limit liability.
9CM4120 Unit Operations Lab Piping Systems ASME Boiler and Pressure Vessel CodeASME B31: Code for Pressure PipingANSI Standards – dimensions for valves, piping, fittings, nuts/washers, etc.ASTM Standards for piping and tubeAPI – Specs for pipe and pipelinesAWS, ASHRAE, NFPA, PPI, UL, etc.Many professional and standards associations have developed codes and standard practices for the design, assembly, and testing of process piping.Depending on which industry segment, which part of the plant, the type of service (drinking water vs. oil pipeline) or the type of construction, you would refer to the appropriate code or standard.ASME boiler and pressure vessel code and B31 are most relevant to ChEANSI – American National Standards InstituteASME – American Society of Mechanical EngineersASTM – American Society for Testing and MaterialsAPI – American Petroleum InstitutePPI – Plastic Pipe InstituteAWS – American Welding SocietyPFI – Pipe Fabrication Institute
10CM4120 Unit Operations Lab Piping Systems ASME B31 Pertinent sectionsB31.1 – Power plant boilersB31.3 – Chemical plant and refinery pipingB31.4 – Liquid petroleum transportB31.7 – Nuclear power plant radioactive fluidsWithin a chemical plant, one section will govern in one part of the plant.In other parts of the plant, a different section may govern the design and installation.
11CM4120 Unit Operations Lab Piping Systems ASME B31.3 – Chemical Plant and Refinery Piping CodeIncludes piping systems in:Chemical and refinery plantsPharmaceutical and food processingTextile and paper plantsBoilersMost important for chemical engineers
12CM4120 Unit Operations Lab Piping Systems ASME B31.3 covers:Materials of constructionPiping design processFabrication, Erection, AssemblyDesign of supportsExamination, inspection, and testingNeed to be familiar with B31.3 if you have plant responsibilities.Code is laid out in sections, starting with scope and definitions and progressing thru design, inspection, and testing.
13CM4120 Unit Operations Lab Piping Systems Piping Design Process – a three step approachDesign for FlowFind min. diameter to achieve desired flow velocityDesign for Pressure IntegrityFind min. wall thickness for process and external conditionsFind appropriate rating of in-line componentsRe-check for Flow Criteria
14CM4120 Unit Operations Lab Piping Systems Standard Pipe SizesDiameters are “Nominal”Sizes 12” and less, nominal size < ODSizes 14” and over, nominal size = ODWall thickness inferred thru “Schedule”Defined Schedules:5, 10, 20, 30, 40, 60, 80, 100, 120, 140, 160Specs for piping found in ANSI B36.10 and B36.19Attempt made to manufacture pipe systems to handle classes of allowable working pressure so that all diameters of pipe of the same pressure rating would be compatible.“Schedule”Higher the schedule, the thicker the wall, the higher the working pressureThe OD stays the same for all pipe of the same nominal diameterExample: 4” schedule 40 pipeOD = 4.50”ID = 4.026”
15CM4120 Unit Operations Lab Piping Systems Standard Tubing SizesSteel tubingDiameters are Actual ODWall thickness is specifiedRefrigeration TubingSingle wall thickness available for each sizeActual ODCopper Tubing – Nominal sizesType K, L, MPipe is always round, tubing can be round, oval, or rectangular/squareTubing specifications in ANSI B32.5Example: Steel tubing4” X ¼”4” OD3 ½” IDRefrigeration tubing:¾”¾” OD w/ 0.035” wall for 0.680” IDCopper TubingType K is thickest2” type KOD = 2.125”Wall = 0.083”ID = 1.959”
16CM4120 Unit Operations Lab Piping Systems Criteria for Design for FlowEconomicsServiceable over Design LifeSmallest diameter usually is lowest costPerformanceMinimum entrainment velocityPrevent erosion or cavitationFirst step is to determine appropriate flow velocity for each piping segment.Find minimum pipe ID to attain the velocity.Select the next largest available size of Standard Weight pipe.
17CM4120 Unit Operations Lab Piping Systems Design Rules of Thumb when sizing for velocity...Water lines: ft/secPump discharge: ft/secPump suction: (1/3 x discharge velocity)Steam: low pressure (25 psig or less) ft/sechigh pressure (>100 psig) ft/secSlurries: > min. entrainment velocityfrom Peters and Timmerhaus, Plant Design and Economics for Chemical Engineers, 4th ed., McGraw-Hill, 1991.Reduce pumping lossesMinimize noise levelsSlurries – need to keep solids entrained and prevent sedimentationPump suction lines – need to minimize head loss in suction piping so that fluid doesn’t vaporize in/at pump
18CM4120 Unit Operations Lab Piping Systems Selecting appropriate pipe ScheduleSchedule = P/S * 1000P = max. working pressure of pipe, psigS = allowable stress in piping material, psiFor carbon steel pipe, S = 36,000 psiWhat is max. working pressure for Schedule 40 Carbon Steel pipe?Ballpark estimate useful for costingStill need to check actual wall stress at process conditions.
19CM4120 Unit Operations Lab Piping Systems Determine min. req’d wall thickness:Pressure Integrity Design MethodASME B31.3,ASME B31.3 uses Pressure-Integrity design method for determining the min. wall thickness.All design factors are included in the appropriate code.Need to reduce pressure ratings for high-low tempNeed to add mat’l for corrosion/erosion allowanceNeed to add mat’l for external loadsNeed to add material for threading, grooving, other material removal processtm=min. wall thicknessP=design pressure, psigD=O.D. of pipe, in.S=allowable stress, psiE=weld joint efficiencyy=factor to adjust for tempA= add’l thickness for corrosion, external loads, etc.
20CM4120 Unit Operations Lab Piping Systems After determining wall thickness:Re-check ID for velocity;Select in-line components;Determine insulation, coverings, coatings;Design and locate supports and hangers.Heavy wall pipe may have reduced the ID below the min allowable based on flow velocity criteria.
21CM4120 Unit Operations Lab Piping Systems Inline Components:FittingsValvesGaskets, Seals, and Thread SealantsConnection Hardware – Bolts, studs, nuts, washers
22CM4120 Unit Operations Lab Piping Systems Pipe Fittings - SteelForgedCastMalleable IronSelect “Class” of Fittings150 lb., 300 lb., 600 lb., etc.Need a look-up table to determine max. allowable P at the design temperatureUsed to connect or adapt pipe to other pipe or equipment.Used to change directions.Used to change pipe diameter or terminate a pipe run.Forged Steel in threaded or socket weldCast Iron, bronze, brassMalleable Iron generally in threaded
23CM4120 Unit Operations Lab Piping Systems Ratings for flanged steel pipe fittings, ANSI BMaximum Allowable non-shock Pressure (psig)Temperature (oF)Pressure Class Rating for Flanged Fittings (lb)15030040060090015002500Hydrostatic Test Pressure (psig)45011252225335055759275-20 to 100285740990148022203705617020026067513502025337556252306558751315197032805470635845127019003170528050017080012001795299549901405507301095164027354560650125535715107516102685447570011071010651600266544407509550567010101510252042008041082512352060343085065270355805134022305034551586014309503510520531010002070155430Select appropriate class, check for availabilityLook for special conditions like need for long radius ells or clean-outs.
24CM4120 Unit Operations Lab Piping Systems Design Checklist:Re-check ID for velocity;Select in-line components;Determine insulation, coverings, coatings;Design and locate supports and hangers.
25CM4120 Unit Operations Lab Piping Systems Piping InsulationPrevent heat loss/ gainPrevent condensation – below ambientPersonnel protection – over 125oFFreeze protection – outdoor cold climatesFire protectionNoise controlInsulating material and covering systemIf the pipe is exposed to washdown or is installed outdoors, need to consider the effects of water on insulating material.Must consider:physical abuse of insulating systemlocation of supportsproximity to adjacent runs of pipeconnections to equipment, valves, and instrumentationMost insulating systems also include a protective covering of cloth, metal, or plastic.
26CM4120 Unit Operations Lab Piping Systems Recommended minimum Thickness of Insulation (inches)*Nominal Pipe Size NPS (inches)Temperature Range (oC)Temperature Range (oF)Hot WaterLow Pressure SteamMedium Pressure SteamHigh Pressure Steam< 1"1.01.52.02.51 1/4" - 2"2 1/2" - 4"3.05" - 6"3.5> 8"* based on insulation with thermal resistivity in the range ft2 hr oF/ Btu inSource: Engineering Toolbox,
27CM4120 Unit Operations Lab Piping Systems Common Types of InsulationMineral FiberFiberglasRock woolCellular glass(Asbestos or Asbestos-containing)Polymeric closed cell foamsFlexible – polyethyleneRigid foam – polystyrene, polyurethanes
28CM4120 Unit Operations Lab Piping Systems Fiberglass Insulation w/ Asbestos-plastered fitting coveringsPlaster of Asbestos was hand-formed around each fittingOften these systems were cloth covered.
29CM4120 Unit Operations Lab Piping Systems Metal Jacketedinsulation coveringJacketing can be aluminum, galvanized steel or stainless steel.This is embossed aluminum – indoor application.Also pre-formed plastic is available.
30CM4120 Unit Operations Lab Piping Systems After determining wall thickness:Re-check ID for velocity;Select in-line components;Determine insulation, coverings, coatings;Design and locate supports and hangers.
31CM4120 Unit Operations Lab Piping Systems Piping Supports
32CM4120 Unit Operations Lab Piping Systems SupportsPrevent strain at connectionsPrevent sagAllow for expansion/contractionDesign for wind, snow/ice, earthquakeProvide clearance for plant traffic/equipmentDetermining max. space between supports is part of design process.
33CM4120 Unit Operations Lab Piping Systems Steel Pipe - Distance between Supports (ft)Outside Diameter (in)Horizontal RunVertical Run1/24.5103/47.511 1/4121 1/22152 1/23418Source: Engineering Toolbox,
34CM4120 Unit Operations Lab Piping Systems Inadequate support
35CM4120 Unit Operations Lab Piping Systems Effect of Thermal Expansion on piping and supportsExample 1:Calculate the expansion per 20’ length of 2”, schedule 40 carbon steel steam line at boiler startup for a 100 psig steam service.α=thermal expansion coefficientfor mild steel, α =6.6x10-6 in/inoF
36CM4120 Unit Operations Lab Piping Systems Temp of pipe at amb. cond. =70oFTemp of 100 psig sat. steam =338oFΔT=268oFL=20’=240”expansion due to temperatureincrease is α *L* ΔT=(6.6x10-6in/inoF)*(240in)*(268oF)=0.42” in per 20’ of pipe
37CM4120 Unit Operations Lab Piping Systems Example 2:What force is exerted on the end restraints of that 20’ pipe if it is rigidly installed (end restraints can’t move)?σ=internal stress due to ΔT, andσ = α *(ΔT)*EE is the material property called Modulus of Elasticity, relationship between stress and strainE=30x106 psi for low carbon steel
38CM4120 Unit Operations Lab Piping Systems =(6.6x10-6 in/inoF)*(268oF)*(30x106lbf/in2)=53,000 lbf/in2since σ=F/A,The force on the end restraints is F=σ*Awhere: F=force in lbfA=cross sec. area of 2”, sched pipe in sq. inches
39CM4120 Unit Operations Lab Piping Systems A=Π(OD2-ID2)/4= Π( )/4=1.07 sq.inF= σ*A=(53,000 lbf/in2)*(1.07 in2)Force on the end restraints = 57,000 lbfor 28.5 tons
40CM4120 Unit Operations Lab Piping Systems Results of inadequate support: Flixborough, EnglandMay, 1974 – Leaking reactor #5 removed from train of 6 reactors and temporarily replaced with a section of 20” pipe. Pipe is supported by scaffolding.June 1, 1974 – Supports collapse, pipe breaks28 dead, 89 injured, 1800 houses damaged, 160 shops and factories damaged, large crater where plant stood20 inch pipe ruptured, possibly due to fire in an adjacent 8” pipe that had been burning for an hour40 metric tons of cyclohexane vaporized and explodedFires continued to burn for 10 daysExplosion occurred on a Saturday or an additional 500 workers would have been killedThe official inquiry into the accident determined that the bypass pipe had failed due to unforeseen lateral stresses in the pipe during a pressure surge. The bypass had been designed by engineers who were not experienced in high-pressure piping design, no plans or calculations had been produced, the pipe was not pressure-tested, and was mounted on temporary scaffolding poles that allowed the pipe to twist under pressure. It should be noted that the by-pass pipe was a smaller diameter (20") than the reactor flanges (24") and in order to align the flanges, short sections of steel bellows were added at each end of the by-pass - under pressure such bellows tend to squirm or twist.Further investigation led to new theories in The test results released in November 2000 seemed to back up Mr Ralph King's theory that the presence of water inside the reactors and the simultaneous shutting down of crucial equipment, generated a massive build-up of pressure that blew the valve apart.Source: Flixborough Disaster, Wikipedia, 3/18/2009
41CM4120 Unit Operations Lab Piping Systems Heat Tracing
42CM4120 Unit Operations Lab Piping Systems Heat TracingPrevents flow problems in cold climatesFreeze protectionLoss of flow due to viscosity increasePrevent condensation in vapor linesMethodsElectricHot FluidsHeat tape or pipe runs along side of process pipe.Induction heating of the pipe can also be used.Steam is most common fluid.Glycols in a recirculating system.Insulation covers the pipe and heat tracing.
43CM4120 Unit Operations Lab Piping Systems References:Piping Handbook, 7th ed., Nayyar, McGraw-Hill, New York, 2000.Plant Desing and Economics for Chemical Engineers, 4th ed., Peters and Timmerhaus, McGraw-Hill, 1991.Valve Handbook, Skousen, McGraw-Hill, New York, 1998Flowserve Corp., SeptThe Engineering Toolbox, Sept
44CM4120 Unit Operations Lab Piping Systems Materials – Metallic pipingCarbon and low alloy steelDuctileInexpensive and availableEasy to machine, weld, cutSome drawbacksCan be cut, welded or threaded, and assembled using commonly available skilled laborSubject to Embrittlement failurescausticshigh pressure steamConversion of carbides to graphiteexposure to high temp over timeSubject to hydrogen stress cracking
45CM4120 Unit Operations Lab Piping Systems Materials – Metallic pipingAlloy Steels including “Stainless Steels”Good corrosion resistanceMore difficult to machine, weld, cutSome drawbacksRequires special welding techniquesHarder to cut, thread and machineStress corrosion failuresexposure to chloridesEmbrittlement failureAfter exposure to high temp (welding without annealing)
46CM4120 Unit Operations Lab Piping Systems Materials – Metallic pipingNickel, Titanium, Copper, etc.Copper is used in residential and commercial applications and is widely availableOther materials are expensive and difficult to machine, weld, joinSome incompatibilities with each
47CM4120 Unit Operations Lab Piping Systems Materials – Non-Metallic pipingThermoplasticsWide range of chemical compatibilityLight weightEasily cut and joinedLow temperature limitsNeed extra supports
48CM4120 Unit Operations Lab Piping Systems Materials – Non-Metallic pipingFiberglass Reinforced PipeWide range of chemical compatibilityEasily cut and joinedWider temperature limits than thermoplasticsThermal expansion similar to carbon steelSimilar structural performance as carbon steel
49CM4120 Unit Operations Lab Piping Systems Materials – OthersGlassConcreteLined or coatedRubberCementTeflonZinc (galvanized pipe)Double Containment piping systemsUsed for low cost, corrosion resistance, long life, ease of cleaningLined pipe is chemical resistant inner layer with structural outer layer
50CM4120 Unit Operations Lab Piping Systems Pipe JointsThreadedWeldedSoldered/ BrazedGluedCompressionBell and spigotUpset or expandedMost common are threaded and weldedThreaded – up to 2”Welded – butt welded or socket weldedUpset – for thin wall pipe and tubing
51CM4120 Unit Operations Lab Piping Systems Threaded joints
52CM4120 Unit Operations Lab Piping Systems Soldered joints
53CM4120 Unit Operations Lab Piping Systems Welded joints
54CM4120 Unit Operations Lab Piping Systems Compression joints
55CM4120 Unit Operations Lab Piping Systems Mechanical jointsshown on glass drain piping system
56CM4120 Unit Operations Lab Piping Systems Fittings for joining 2 sections of pipe:CouplingReducing CouplingUnionFlangeCouplings join two lengths of pipeReducing couplings used for joining two lengths of pipe of different diameters. Can be concentric or eccentric.Unions and flanges are used when piping must be dis-assembled
57CM4120 Unit Operations Lab Piping Systems Fittings for changing directions in pipe:45o Ell90o EllStreet EllBoth short and long-radius fittings available
58CM4120 Unit Operations Lab Piping Systems Fittings for adding a branch in a run of piping:TeeCross
59CM4120 Unit Operations Lab Piping Systems Fittings for blocking the end of a run of piping:Pipe plugPipe capBlind FlangeCaps, plugs, and blind flanges are used to block off the end of a pipe
60CM4120 Unit Operations Lab Piping Systems Misc. pipe fittings:NippleReducing bushingNipples lengths up to 12 inch standard, other lengths availableReducing bushings are typically used to reduce the size of a tank or vessel fitting to the size of the pipe run.Not normally used as in-line fittings.
61CM4120 Unit Operations Lab Piping Systems Gate Valve:Used to block flow (on/off service)Sliding “gate”on knife-gatevalve
62CM4120 Unit Operations Lab Piping Systems Globe Valve:Used to regulate flowCut-away showsstem sealplugand seat
63CM4120 Unit Operations Lab Piping Systems Ball Valve:Typically used as block valve“Quarter-turn” valveCut-away shows ball and seat
64CM4120 Unit Operations Lab Piping Systems Butterfly Valve:Can be used for flow control or on/offValve actuator/ positioner for accurate flow control
65CM4120 Unit Operations Lab Piping Systems Check Valves:Used to prevent backflowPiston checkSwing check