elements of pipeline design

7/28/2019 Elements of Pipeline Design

1/21

~ h a p t e r 1ELEMENTS OF PIPELINE DESIGN

H.iCIIONThis chapter provides an overview of elements that systematically influence pipeline designtllrough to constmction, operation, and maintenance. Subsequent chapters provide detailedinfonnatIon on these topics.

Pipelines atIect daily lives in most parts ofthe world. Modero people's lives are based00 (In environment in which energy plays a (predominant) role. Oil and gas are majorparlicpants in the supply of energy, and pipelines are Ihe primary means by which they aretransported. l t is no coincidence that an extensive pipeline network goes hand-in-hand witha high standard of living and teehnological progress.

Among other uses, oil and gas are utilized lo generate electrical power. Usingclectricity/oil and gas directly, houses are heated. meals are cooked, and a comfortableliving cnvironmcnt is created. Petrochemical processes also use oil and gas to make usefulproducts.

To fulfil the oil and gas demand for power gcncration, recovcry processcs, and otherj"Ldines are utilized to Iransport the supply from their source. These pipclines are

,nl.';!!Y buried and opcrate without disturbing normal pursuits. Thcy carry large volumes ofn"il':al gas, cmde oil, an d other products in continuous streams.

:onstruction procedures for most pipeline systems can be adapted to consider specific:, ,n mental conditions and are tailored to cause mnimal impact on the environment.Unattended pumping stations move large volumcs of oil and pctroleum products under

high pressure. Similarly, natural gas transmission systems, supported by compressorstations, dcliver large volumes of gas to various consumers.

Many tactors huve to be considcreo in thc engineering and design of long-distanceplpclmcs, including the naturc and volume of fluid lo be transported, Ihe length ofpipe\ine,the types of terrain traversed, and Ihe environmental conslraints,

To obtuin optimum results for a pipeline transmission system, complex cconomic andcngineering studies are necessary to decide on the pipeline diameter, material, comprcssionlpumping power requirements, and location of the pipeline route.

Major factors influencing pipeline system dcsign are:

Fluid properties Design conditions Supply and demand magnitude/locations eodes and standaros Route, topography, and access Environmental impact Economics "" : !ydrological impact Seismic and volcanic impacts


2/21

2 Pipel ine Design and Construction: l\ Practical Approach Material Construction Operation Protection Long-term Integrity

FLUID PROPERTIES The properties oftluid to be transported have significant impact on pipeline system designoFluid properties are either gven for the system design or have to be determined by thedesign engineer. The following properties have to be calculated for gas at a specific pressureand temperature:

Specific vo/umes Super compressibiIity factor Specific heat Joule-Thompson coefficient Isentropic temperature change exponent Enthalpy Entropy Viscosity

For liquid (such as oil or water): Viscosity Density Specific heat

ENVIRONMENT

The environment affects both below- and above-ground pipeline designo For below-groundpipelines, the foIlowing properties have to be determined during system design:

Ground temperature Soil conductivity Soil density Soil specific heat Depth of burlaI

In most cases, only air temperature and ai r velocity have a significant impact on the designof above-ground facilities.

For both below- and above-ground pipelines, ground stability influences pipelinedesign/the pipeline support system. Significant variations in ground elevation particularlyaffect liquid pipeline designo


3/21

Elements of Pipeline Design 3Of: PRISSlJRE AND TEMPERATlJRE

GeneralTemperature and pressure influence all fluid properties. A temperature rise is generallybeneficial in liquid pipelines as it lowers the viscosity and density, thereby lowering thepressure drop. A temperature rise lowers the transmissibility of gas pipelines due to anincrease in pressure drop. This results in a net increase in compressor power requirementsfor a given flow rate. The value of absolute (dynamic) viscosity for gas increases with anincreasc in pressure and temperature. Such an increase will result in an increase in frictionalloss along the length of the pipeline. ,,'Iine temperature also impact


4/21

4 Pipeline Design and Construction: A Practical ApproachAIR TEMPERATURE =25 oC GROUND SURFACE 18 oC

E E oooT""

EEoooC\J

2200 mm

Figure 1-1. Temperature isotherms around a buried pipeline after 30 days (summer season)

Friction factor I fOT a fully turbulent flow is given by the ColebTOok-White equation:

r ; - [( 1.25) 1IIi] (I 2)viiI =410g 3.7d + Re x vii!


5/21


6/21

6 Pipeline Design and Construction: A Practical i\pproach

10

L()ooo!I

C\JEJ)Z 0.1'"E(J)z>-1-5Or:J):;: 0_01

RATE OF SHEAR S1 (Represenls Different Fluid Velocities) 0.6

192

9,6

192

Non-New1onianBehavior )-----..... NewtonianBehavior

Is 10 20 30 40 50 60TEMPERATURE, oC-

'--- - -- Typical BitumenTypical Bitumen -Dilutent Blend

Figure 1-3. Viscosity characteristics for typical non-newtonian fluids

e=2.718 ... , naturallogarthm bases=gas density factor (lo allow for elevalion change) C4 ( ~ L - ) G1 fa Z aTb, Pb=base temperaturc and pressureTra flow temperature (average for segment)Za""compressibility factor (average for segment)C I , e2, C1, C4 =constants

The expression J1TJ is also sometimes referred to as the transmission factor, F.From the analysis ofEquation (1 1), applicable to liquid hnes, it can be inferred that forconstant mction and elevation, pressure 10ss (Pi - P ) is directly proportional to flow. Such a

pressure loss (converted to head) when plotted on a distance elevation scale will represent astraight line called the hydraulic gradient. In pipeline design, the hydraulic gradient mustnever cross the pipeline elevation pro file, else the Iiquid will not be able to clear theeIevation high point.

The analysis of gas pipeline Equation (1-3) indicates that for constant mction factor thepressure los s and flow do not have a linear relationship.

-------_._--


7/21

Elements of Pipeline Design 7Friction Factor Retative Aoughnesso : : ~ ~ ~ ~ W

O_t)'

Figure 1-4. Moody diagram fnction factor for flow offluids in pipelines [Moody 1944]

Re" ;ewing Equations 1 l through 1-4, it is also significant to note the interrelationshipbct\vcen friction factor and pipe roughness, diameter, and Reynolds Number (Re), which isrclatcd to fluid Viscosity (/1.), density (p) and flowing velocity (V). Such a relationship is\Vell dericted by the Moody diagram (Moody 1944) shown in Figure 1-4.

Changes in elevation alter the flow velocity. Also, changes in temperature along thepipeline alter viscosity and density. The rcsult in each case is that the friction changes. It isimportant not to confuse friction with pipe roughness. Roughness is the pbysical )haractenstic of a pipe and is generally constant at any given time and location, but it is ifriction that changes within the pipeline.

1ly /OEMANO SCENARIO, ROUTE SElECTIONSupply and delivery points, as well as demand buildup, affect the ovcrall pipeline systemdesigno The locations of supply and delivery points determine the pipeline route and thelocations of facilities and control points (e.g., river crossings, energy corridors, mountainpasses, heavily populated arcas). The demand buldup determines the optimum pipelinefacilities size, location, and timing requirements.

Following the identification of supply and delivery points, and as a prelude to pipelinedesign, a preliminary route selection is undertaken. Such a preliminary mute selection isgenerally undertaken as follows:

l. ldentification of supply and delivery points (1 :50000 map). 2.. inentification of control points on the map.


8/21

8 Pipeline Design and Construction: A Practical Approach3. Plot of .shortest route considering afeas ofmajor concem (high peaks, water loggedterrain, lakes, etc.).4. Plot of tbe seJected route 00 aerial photographs and analysis of the selected routeusing a stefeoscope to ascertain vegetation, relative wetness, suitability of terrain,construction access, and terrain slopes, etc.5. Refinement of the selected route to accommodate better terrain, easier crossings,etc.This preliminary route selection is ofien examined by aerial reconnaissance and on-stevists to ensure me pipeline route and potential facility 10catons are feasible prior todetailed survey. Detennining the pipeline route will influence design and construction inthat it affects requirements for line size (lengtb and diameter), as well as compressor orpumping facilities and their location. Hydraulics, operational aspects, and the requirementfor special studies in areas where the pipeline traverses unstable ground in highly wet andcorrosive soil are generally established at this stage.The economically optimum sizes of facilities required for the entire range of possbleflow rates are determined by the supply and demand buildup data. This data also influencesthe timing and location of the facilities and whether additional metering stations,compression/pumping facilities, or looping wiII be required.

eODES ANO STANDARDSPipelines and related facilities expose the operators, and potentially the general public, tothe inherent risk ofhigh-pressure fluid transmission. As a result, national and intemationalcodes and standaros have been deve\oped to limit the risk to a reasonable minimum. Suchstandard s are mere guidelnes for design and construction of pipeline systems. They are notintended to be substitutes for good engineering practices for safe designs.Major codes affecting pipeline design are listed in Table 1-1. Sorne Federal and othergovemmental authorities have the right to issue regulations defining mnimum requirement !for the ppeline and related facilities. These regulatons are legally binding for the design, \\construction, and operation of pipeline system facilities, which are undcr the jurisdicton of Ithe relevant authority. \'There are also a number of other authorit ies (e.g., u tili ty boards) who have jurisdiction .over specific concems with regard to pipeline design and construction. These authorities jhave the right to enforce thei r own regulatons , setting mnimum requirements for pipelinefacilities within their jurisdction.

ENVIRONMENTAL ANO HYDROLOGICAL eONSIDERATIONSEnvi ronmental

The environmental evaluation of a pipeline route is an integral component of its design andconstruction. It requircs special planning to ensure effective and suecessful protecton andreclamation procedures. InitialIy, resources in the immediate area of the pipeline route areidentified and assessed to determine potental impacts. Although site-specific, resourcesthat are usualIy considered in an evaluation are wildlife, fisheries, water crossngs, forest


9/21

Elements of Pipeline Design 9TA8lE 1-1. List of majar organization codes and standards affecting pipeline design,

construction an d operationAuonym Organization/topic

ACIAGAANSIAPIASMEASTMeSADEPIEEEIPISAISOMSSNACENAGNEMANFPASISSSPCANSI 816.5ASTM A 350MSS SP-25MSS SP-44API 5LAPI6DAPIII04 (NAG 100)ASTM A 333 or ASTM A 106ANSI B16.9ASTM A 234 or ASTM A 420ASTM A 350 or ASTM A 105ANSI B16.11ANSI!ASME 13::11.4ANSIIASME ml.8ANSI B16.9ANSI B16.10DEP 3U801. l0 ANSI B 16.34ANSI B IlANSI B95.lDvsion 1, Rules fOf Constructon ofI'rcssure VesselsQualification Standards [or Weldingand 8razing 1'roceourcs, Wclders,I3razers, Weldng, ano Brazng OperatorsMSS SP-53

MSS SP-54

MSS SP-55MSS SP-75API RF 6FA1'1601API RP 520API526APU27ASTM AI06

American Concrete InstituteAmerican Gas AssociatonAmerican NationaJ Standard InstituteAmerican Petroleurn InstituteAmerican Society of Mechanical EngineersAmerican Socid.y rOl' Testing MaterialsCanadian Standards AssociationDesgn Engineering PractceInstitute of Electronic and Electrical EngineersInstitute of PetroleurnInslrument Society of AmericaIntemational Standards OrganizationManufacturers Standardization SocietyNational Association of Corros on EngineersNormas Argentinas de GasNational Electrical Manufacturing AssociationNational Fire Protection AssociationStandard s Institu te of SwedenSteel Structures Painting CounclPipe Flanges and F1anged FittingsPipe Flanges and Flanged Fittings MaterialStandard Marking Systern for Valves, Fittngs, Flanges, and UnionsSteel Pipe Line FlangesAPI Specitications for Line PipeSpecifications for Pipeline Valvcs, End Closures, Connectors. amiSwivclsWelding of Pipeline and Relateu FacilitiesMaterials for Surface Installations PipingButt Welding ElbowsiTeesl3utt Welding Elbows/Tees .\t1atcralsForged Fttings


10/21

10 Pipeline Design and Construction: A Practical ApproachTABLE 1-1. (Continued)

Acronym Organization/topicASTM A2J4ASTM A694ASTM AI93ASTM AJ94ASTM A370ASTM E384CAN/CSA 2662CANJCSA Z245.20-M92CANICSA Z245.21-M92 and DIN30670IDlN 30671API RP SUSSPC-SPI SSPC-SPIO SSPC-VIS-I SIS 05-5800-1967 SPSC-SP3 ASTM G8-72 NACE RP-OI-92 NACE RP-05-72NACE RP-OI-77NACE RP-02-86NACE RP-02-74IP Part I TP Part 15 DEP 33.64.10.10 API500c AGA3 AGA8 AGA9 ANSI B40.1 IP Part J ISA ASTM-A36 ASTM-A82 ASTM-A/84 ASTM-AI85ASTM-AI96 ASTM-A615 ASTM-C33 ASTM-C39 ASTM-C94 ASTM--C I36 ASTM--C150 ASTM--CI72 ASTM-IJ422 ASTM-D698 ASTM-DI557

_. ASTM-D2049ASTM-D4318ISO 9001

Pipe Fittings of Wrought Carbon SleeJ and A1I0y Sleels for Moderateand Elevated Teml'el1l.turesForging, Carbon and Alloy Steel. for Pipe Flanges, Fttings and Valves,and Parts for High-Pn:ssure TransmissionAlloy Steel and Stainless Steel Boltng Materals for High-TemperatureServiceCarbon and Alloy Stee\ Nuts and Bolts for High-Pressure and HighTemperature ServiceMethods and Defiotioos for Meehanical Testing of Sleel ProduclsTest Method for Microhardness of MalerialsOil and Gas Pipeline SystemsExternal Fusion Bond Epoxy Coaled Steel PipeExternal Polyethylene and Thermoplastic Coating for Une PipesRecomrnended Practice ror Internal Coating of Line Pipe tor GasTransmission ServiceSurface Preparation - Solvent CleaningSurface Preparaton Specification No. 10, Near-White BlastcleaningPietoral Surface Preparaton for Paintea SurfaeesPictoral Surface Preparaton Standard for Pantng Steel SurfacesPower Tool Cleaning as per Steel Structure Painting CouncilStandard Test Methods for Cathodic Disbonding of Pipeline CoatingsControl of External Corrosion on Underground or Submerged PipingSystemDesign, Installaton, Operation, and Maintenance of Impressed CurrentDeep GroundbedMitigation of Altemating Currenl and Lightning Effeels on MetallicStructures and Corrosion Control S y s t e m ~Mitigaton of Altemating Current and Lightning Effects on MetallieStructures and C o r r o . ~ o n Control S y s t e m ~llgh Voltagc Electrieal Inspection of Pipeline Coatings Prior tolnstallationModel Code of Safe Plactice, Electrical Safety CodeArca Classification Code for Petrolcum InstallalionElectrical Enginecrng GuidelineHazardous Area ClassificationMeasurement of Gas by Orfiee MetersDetermination of Supereompressibility Factors for Natural GasMcasurement of Gas by Turbine MctcrsGauges and Pressure Indicating Dal Type, Elastic ElementModel Code of Safe Praclice, Eleclrical Ch. 3 Instl1lmentationStandards and Praenees for Instl1lmcntatonStruetural Steel Manual of Steel ConstrnctionSpeciflcalon for Cold-Orawn Sleel Wire lor Concrete RenforcementSpecificatons for Fabricated Deformed Steel Bar Mats for ConcreteReinforeemenlSpecitkaton for Welded Sleel Wire Fabric for Concrete ReinforcementSpecification for Sleel Wire, Defonned, for Concrete ReinforcemenlSpecification for Deforrned and Plain Billet-Steel Bars for ConcreteReinforcementSpecification for Concrete AggregatesTest for Cornpressive Strength of Cylindrcal SpecimensSpecfication for Ready-Mixed ConcreteTest for Sieve or Screen Analys s of Fine and Coarse AggregatesSpecification for Portland CernentMethod of Samp1ing Freshly Mixed ConcretePartieTe Size Analysis ofSoilMoisture Density Relations of Soil and Soil Aggregate Mixtures Usng5.5 lb. RarnmerTest for Moisture-Density Relations of Soils and Sol AggregateMixtures Using 10 lb. Rammer and 18 in OropStandard Method ofTest for Relalive Densty of Coheson SoilsTest for Liquid Limit, Plastic Limit and P l a ~ t i e t y lndex of Soilfor DesignlDevelopment Production, Installation,
http:///reader/full/33.64.10.10http:///reader/full/33.64.10.10


11/21

11lernents of Pipeline Oesign ('()Ver, and archaeological and palaeontological resources. A soil and vegetation evaluation:i also conducted to detennine soil handling and reclamation procedures.Land use in the immediate area of dJe pipeline route is also identified and evaluated tollsure that conflcts do not alise with other companes or individuals. Protecton proceduresare based upon these resource assessments and are then integrated into the designparameters of the pipeline construction and specitlcations.Timing for pipeline construction is also taken into consideration in the evaluation ofresources, as seasons can eftect lhe se/ection of the most appropriate mitigative procedures.( 'ntlstruction techniques that are effective during the summer may not be appropriate or

d T ( ~ c t i v e in the winter.Alternatively, dealing with site-specitlc resource impacts may create conflicting timing) ~ t r a i n t s with those of proposed construction schedules.Specialized techniques to reclaim the construction right-of-way are implemented:llowing mainline construction. Every attempt is made to match existing species for".'\ q ~ e t a t i o n purposes to ensure successful reclamation of noncultivated lands and to retumullvated lands to their previous agricultural productivity.Durng construction of the pipeline, environmental inspection is ongoing to ensure. 'l1plinnce with environmental desgn and protection procedures, and to maintain""istl'Ocy with various regulatory approvals. Problems that are identif1ed during theH'n :md construction phase of the project are reviewed internally and may initiateenvronmental research, which in tum may rnodifY future design critera.In


12/21

12 Pipeline Design and Construction: f\ Practical Approach Sand plugs Temporary eover Sediment/silllIaps Canals/disturbances Volcanic afeas (if applicable) Permanen t physical eros ion control method 50ft plugs Revegetationlrcgrading Drainage system Bennlgabions Ditch roam plugs Agronomic erosion control Revegetation measures schedule Procedures and methods Revegetation plan

HydrologicalA pipeline may be subjeet to buoyant forces due to water mgration and floodng or watcrcrossings. The design must consider the potential for damage to the pipeline due to floodplans and the neeo for dredging of watercrossings, scounng, or channel shifting in order todetermine the correct pipeline design and instaIlation teehnique. The design may need toconsider the determination of pipe depth, buoyancy control, pipeline installation, andconstruetion methodology in arcas of hydrological coneern. Usually facilitics are designedsuch that thcy will not sustain an y unantieipated oamage from a l : 100 year 1100d, and willfulIy and continually operate under 1:50 year flond conditions. lIydrologieal conditions andscouring evaluations should be undertaken for major river erossings with established 1 50years and 1:100 ycars flood plnins.

EC()NOMICSGeneral

Th c cconomes of transportng fluids by pipelines affeet almost all design andconstruction parameters. For any pipeline project, the objective of economic analysis isto determine which of the altematve design and construction solutions offers thc besteconomic advantage (Mohitpour 1977). Economic analysis is carried out to determine theoptimum choice between size of pipelines (diameter, wall thickness, and material) andcompressionlpumping power requirements. An economc analysis is also needed forutility purposes, to define tariffs that have to be charged for the transmission of fluid toachieve a stipulated economic performance of a pipeline system investment (Mohitpourand McManus 1995).

The economic feasibility of a pipelinc project is usually established before anyoptimization takes place. One criterion that is ofien used for acceptance or rejection of aprojeet is the expected rate ofretum on the invested capital. Once the feasibility is proven,


13/21

Elements of Pipeline Design 13optifllum choices between line size and pumping/compression requirements aredctermincd. Timing eonsiderations may be optmized and tariffs may be determined(rnostly lor utility companies).Estimates have to be made for the overall investment requirement and associaledoperating costs ofthe proposed pipeline system. These are the two principal components ofawning and operating a pipel ine system. The relevant eosts for a pipeline projeet have to beeardully considered, covering all phases from planning to operatng and maintaining thepipeline over the course 01' its life. Elements that influence the cost estimate and thereforethe cconomic analysis are outlined in the following subsections.

CO:i1sOireet costs cover expenditure directly related to the design, construction, and operation ofa pipeline system, including the following:

Line pipe CompressionJpumping facilities Meter stations Yalve and fittings Protection facilities (coating plus cathodic protection) Scrapingleleaning facilities if any Pressure reduction facilities Power generation (if applieable) Construction casts .) Engineering eosts o Survey costs ) ('ost of ancllary facil ities ) [,,:gal and land cos ts (ROWacquisition) } I )ocks, wharves :ak detecton system

Lugistie eosts (thosc assoeiated with material and equipment transportation) Operating and maintenanee eosts (those associated with local taxes, fuel, energy,material, and labor costs)'9 Uther costs (Iine fiJl, working capital required lo operate the pipeline, etc.)

Indirect Costslndirect costs affeet the financing of a pipeline project, and inelude costs associatedwith the acquisition of necessary funds to cover the purchase of m*rials and constmction. Indirect costs also cover the interest on money borrowed to friance the pipelineprojcct.

Economic AnalysisOil and gas producing companies may use an economC analysis to justify a pipelineproject over to altemative solutions. Oil can be transported by road or rail. Gas may befed into an existing pipeline network owned by a utility company. In the latter case, atriff for self-ownership is determined an d compared to the tariff charged by the utilitycompany for transportation of gas to the delivery point. The system design is influencedcconomic analysis snce a number of technical solut ions are nvestigated by vary ing


14/21

14 Pipeline Design and Constructjon: A Practical Approachpipeline size, pumping or compression facilities, and the timing of the facility expansion oraddition.

Utility companies are interested in establishing the appropriate tariff lo charge acustomer for transporting the cuslomer's fluid in fue company's Iines. For a selecledpipeline size, given ibat the volume of fluid lo be transported can have an upward trend(as a result of demand buildup), the tariff generaIly decreases as the throughput inereases(Figure 1-5). If the pipeline design or operating conditions are changed, the tariff wi1\ehange. As a result, it is at the design stage that a pipeline economic study is undertakenlo determine the viability of the pipeline system configuration [or all modes ofvolumetricflows,

When the economic viablity of a pipeline project is established, the analysis is usuallyreron using the optimal technical configuration and the most refined cost infonnationavailable. The following additional cost parameters nero to be considered:

Equity investment as a portion of total investment (Ioan-equity ratio) Interest on borrowed capital Duration of borrowed capital (i,e" repayment schedule) Depreciat ion rate of facilities investmcnt for book purposes Depreciation for tax purposes Escalation rate of operation and maintenance cost Required rate of retum on investment Escalation rate on tariff Expected Jife of the pipeline until abandonmentAfter evaluation of all the aboye paramcters, the factor by which the economic viability

of a pipeline system is measured is the rate of retum. The higher the rate of retum, the moreattractive the projec t is trom an investment point ofview, Calculation ofinvestment mte of

TABlE'1-2. Relationship between cost parame!er and cost componen! for cost of serviceItem Descripton

(iross Facilti.:s COSi Allowance filr FunJ During Construction (AFUOC) Rate of Retum (RR) Deprecialioo Net Base Rate ncome Tax Taxable locome Interest Expenses (scrvice cost) Capital Cost Allowance (CCA) Operalion and Maintenance (O&M) CostAnnnal COSI of Service Accumulated Cost of Servce (ACOS)

Present Value of Cost of Service (PVCOS) or '\vl:rage Discounted Unit Cost ofServce (ADUCS) based on volume

Capital Cost + AFUDC + Working CapitalRR x (month ( 12) x Construction Cost(Debt%) x Debt Interest + (Eqnity%) x EquityInterest(Original Cost - Salv age Cost )/Project LifeGross Facilities Cost Accumulated Depreciation[Tax Rate/(I . Tax Rate)] x Taxable IncomeRetum + Depreciation Interest Expenses CapitalCost Allowance (CCA)(Embedded Cost of Debt) x Debt% x Rate Base(Gross Facilities CasI Accumulated Depreciation AFUDC) x CCA rateAdrninistration and General + Actual OperationCostsDepreciation + O&M + Taxes + RetumCurnuJative Cost of ServceJProject Life

where i = Discount Rate andAVOL = Accumulated Volumen = Life of


15/21

---

15lernents of Pipeline Design

(] )E \ NPS 12::J~+Je \::>V)-

NPS16

NPS 24

. ~ .._ ..---JIIOO- Th roughputFigure 1-5. TarifTvs. throughputretum is based on computing relevant cash streams for each calendar year and discountingaccordingly. This type of computation is best suited for computer applications due to therepetitive nature of the ca\culations.Table 1-2 depicts some of the major cost parameters and their nter rclationships withcost componcnts (Asante et al. 1993). Typical results of such an analysis for a liquidpipeline system are shown in Figure 1-6.

For long-distance pipeline systems, (he significant cost in terms ofcapital investment is thecost ofthe pipe material and installation. Pipeline pressure, grade, installation location, andtechnque affect the cost and design (Mohitpour and McManus 1995).Pipe materiaVgrade affect (he wall thiclmess and determine the choice of and limit onthe welding/installation technique. For a given desgn pressure and pipe diameter, the wallthickness decreases with a higher grade material. However, higher grades of steel areusually accompanied by cost premiums and more stringent construction techniques, whichtranslate nto higher costs (Figure 1-7).The location of the pipeline or surrounding environment determines allowable material(e.g., Category 1 versus Category II ) and labor/equipment, including construction materialsrequiremen ts.


16/21

16 Pipel ine Design and Construction: A Practical ApproachCost Parameters: Debt lmerest Rate 11.00% Percentage Debt 55.00% Retunl (J f t Equity 16.00% 4 Percentage Equity 45.00%RequimI Rate of Retum 13.25%Long Tenn Debt Service 6.66%Disawmt Rate (nominal) 15.00%AFDUC Rate 10.00%3 Wot'i.lllg Capital asID() percent of Capital Cost 1.40%O&M Escalation Rate 5.00%ID(f ) Capital Investment US $132 M (1997)'5 5M (2003)

~ 2 58M (2008)(. )uIDEO

I I I I I I1997 2000 2002 2004 2006 2008 2010 2012Figure 1-6. Example of cost of service curve

Depending on the application (Mohitpour 1987), the material requirements, asndicated by the notch toughness, are divided into three categories:Category 1 Requirement: No notch toughness requirement.

Typical application: Low vapor pressure fluids (water, crude oil,etc.).Category II Requirement: Notch toughness in the form of cnergy absorption andfracture appearance.Typical application: Buried and above-ground pipelines (_5C to-45C). high vapor pressure (HVP).

Category 1II Requirement: Proven notch toughness in the forro of energyabsorption only.Typical applcation: High vapor pressure liquids.

OPERATION- -_._-_. . . . . . ----------------------------------The conditions under which a pipeline operates are set at the design stage (Stuchly 1977;Mohitpour and Kung 1986). The design stage should also determine the most stringentconditions the pipeline would operate under and provide for facilities to prevent faHure,including line rupture. An example of the latter is sudden valve c10sure in liquid pipelineswhere val ves are located downstream in a downhill terrain. Such an example is shown in thepaper by Kung and Mohitpour (1986) enttled "Non-Newtonian Liquid Pipeline HydraulicsDesign and Simulation Using Micro computers." Sudden valve closure at such a location


17/21

Elements of Pipeline Design 17(NPS 16, design pressure 10200 kPa)

110t I ,I1000 I 1,I I . , Price per kilometer 100

t./

E.::s:-: 900 ~6 90.g1>Q a.;::.. a.

\\ o::\0080,, ..!, .,I ., .'.........

7 0 0 ~ - - - - - - - - ' - - ~ - - - - - - - - 4 1 - - - - - - - - - - r l - - - ~ - - - - - - r 7 0Grade (API) 5L GRB X42 X56 X65 X70 . WT Ir\lm) 14.3 12.7 9.5 8.7 7.1

Figure 1-7. Typical pipeline grade costcould cause pipeline pressure to exceed the maximum design pressure set by the pipestrength and wall thickness. Without surge-mitigating facilities the pipeline couId rupture,resulting in environmental and mantenance implications.Sudden valve closure n liquid pipclines (e.g., crude oil) may create a low- pressurestuaton that in extreme cases can lead to vapor pockets in the lineo Snce the collapse ofvapor pockets can damage the pipeline, this condition has to be avoided.

External ProtectionBuried pipelines are subject to external corros ion caused by the action and composition ofthe soils surrounding them. During the design stage, the available types of externa' coatingmaterial and cathodic systems required to pro tect the pipeline from external corrosion are


18/21

18 Pipeline Design and Construction: A Practical Approachevaluated. The coating and cathodic protection are chosen according to economics andability to pnoct the pipeline.

External coating is usually a plastie material that is wrapped or extruded onto the pipeor fusion-bonded to the surface. Externa! coatings have to be designed to serve as acorrosion banlcr and to resist damage during transportation, handling, and backfilling.Therefore, in sorne cases corrosion protection coatings are combined with other externalcoatings, such as insulation, rockshield, or concrete.

Internal Protect1ooFluids containing corrosive components such as salt water, hydrogen sulphide (H 2S), orcarbon dioxide/monoxide can cause internal corrosion. Many of the internal corros ionproblems can be corrected in the design stage. This is done by proper design andselection of materials appropriate for the fluid to be transported. An example is thepipeline transportation of sour gas. The typcs of corros ion that can occur in sour gaspipelines are:

Hydrogen-induced corrosion Hydrogen-induced cracking Sulphide stress cracking (hydrogen embrittlement) Pitting corrosion General corros ion Erosion corros ionHydrogen-induced cracking such as blistcring has be en observed in both low- and

high-yield-strength steels under both stressed and nonstressed conditions. Hydrogenblistering and cracking results from the diftuson of atomic hydrogen, produced by thecorrosive eIcmcnts in a we! H2S environment, into the stecl, where it is absorbed inlaminations or nclusions in the pipe walL

The atomc hydrogen changes to nondiffusible molecular hydrogen, building up highlocalized pressures that cause blisters or cracKs in Ihe pipe waUs. The design wilI set thestage tor the protection of the pipe against such a failure by specfying the lmits on thefolIowing:

Quantites 01' eerium or other rare eartb metal s to spheroidize manganese sulphides Leve! of sulphur content Level 01'copper content (up to 0.3%) to reduce the hydrogen absorpton properties of

the slrelThe exact mechanism 01' sulphide stress cracking or hydrogen embrittlernent is not

c1earIy understood; however, it is generally agreed that it is influenced by three f a c t o r s ~environmental, metallurgical, and stress-related. Environmental factors include pH, H2Sconcentration and temperature. Metallurgical variables inelude strength or hardness,ductility, compositon, heat treatment, and microstructure. The susceptibility of a steel tosulphide stress cracking ncreases with increasing hardness and stress and also withdecreasing pH level of Iiquids. Sulphide stress cracking is evidenced as a reduction in thenormal ductility and the embrittlement of steeL

A specification for the line pipe material developed at the design stage ensures that thepIpe produced is suitable for the operating temperature that will be encountered and is not


19/21

Elements of Pipeline Design 19::Ilsecptible to hydrogen-induced corrosion. Pit ting corrosion resul ts from chemical attack atluw points where fluids settle and accumulate in the piping system. Sulphate-reducingbacteria may also cause pitting corrosion.General corros ion results from chemical att ack and usually occurs on the upper half oftlle pipe wall adjacent to low arcas where the pipe wall is altemately wet and dry. The use ofcorrosion inhibtors has proven to be the only effectve method to mtigate intemalcurros on in wet sour gas pipelines. On-stream piggng facilities are generalIy incorporatedinlo the design of the system to permit the removal of lquid accumulation on a schedule.UIl::;tream pigging also improves the distributon of the corrosion inhbitors and is avaluable aid in the mitigation of intemal corrosion.Erosion corrosion results from impingement of fluids/chlorides on the pipe surface at

1 1 1 ! ~ h tlowing velocities. Piping is generally sized to limit flowing velocities below thecritical velocity at which corroson erosion will begn to occur. Critical velocity is definedas the point at which velocity is a significant factor in the removal of inhibitor films orcorros ion products.

PElI" r: F,.\ ffGRITY MONITORINGNo matter how well pipelines are designed and protected, once in place they aresubjected to environmental abuse, extemal damage , coating disbondment, soil movementJjnstability (Wong et al. 1988) and third-party damage. Figure 1-7 ilIustrates an example01' a type of damage recordcd on transmission lines in the United States (Crouch et al.1(94).The goal of any pipeline integrity program is to prevent structural integrity problems'mm having a significant effect on public safety, the environment, or business operations

Chem.ical,Baclelial4.0%

.. EnvironmenLaliy" tm,en[) alerials andConsrrucon

OulSide Force.

~Figure 1-8. Pipeline incidents related to line pipe

, J i


20/21

20 Pipeline Design and Construction: A Practical Approachby identifying and petfonning the most efl'ective inspection, monitoring, and repairactivities.

Integrity Assessment MethodsThere are several tcchniques available to assess lhe integrty ol' the pipeline once it's inplace. These are surnmanzed as l'ollows:

Visual inspccton Oepth ol ' cover survey External nondestructive testing (NOT)

Radiography Magnetic particle testing Oye penetrant inspection Ultrasonic inspection

Cathodic protection monitorng Coatng disbondment and damage survey Hydrostatc testing Geometry in-line inspection (TU) tools

Calper pig x, y, z geometry (inertial guidance) tool

Ultrasonic in-lne inspection tools Conventional magnetic tlux High-resolution magnetic flux (30)

Utilization of high-resolution tools facilitates an accurate prediction ol' external aneiinternal corros ion areas (Grimes 1992).

Risk AssessmentsRisk assessment is an integrity management tool and its purpose is to identify and quantifythe risks associated with pipeline operation. such that remedial action can be performed in atimely manner. This is achieved through the ranking of potential rsk to safety, environment,and operations.

Several risk assessment methods are used by the industry. The most common arefailure probability mcthods and ranking systems. The most approprate method dependsupon several l'actors, including system complexity, availabi!ity of historcal data, and rigorrequired by the analyss (Trefanenko et al. 1992).

Pipeline integrity and management decisions are made much easier by the riskassessment and prioritization process, which establishes a firm, documented basis fordetermining expenditures and schedules (U rednicek et al. 1991).

Pipeline RepairsOnce an integrity assessment method establshes a requirement for pipeline repair, there aresevera! methods that are cornmonly used by the industry to restore pipeline integrty:

Local coating repairs Coating rehabilitation Sleeve repair Cutout repai rs


21/21

Elements of Pipeline Design 21Use of each repair system depends on Ihe extent of damage or corrosion problem, but

repairs are carried out lo restore the integrity of the pipeline to assure its intendedoperational capacity.

B., Luk, w., and Lixing, M., J993, "Pipeline System Optimization: A Case Study of Quinghai GasPipeline," Proc. 12th lnternatonal ASME OMAE Conference, Glasgow, Scotland, Volume V, PipelineTechnology, pp. 385-393.

\SCE, 1975, Committee on Pipeline Planning, "Pipeline Design for Hydrocarbon Gases and Liquids:Report of the Task Committee on Engineering Practice in the Design of Pipelines," New York, NY

A. E., Bubenik, T. A., and Bames, 8. , 1994, "Outlook on In-Line Inspection for Stress CorrosionCracking," Pipeline Pigging & Integrty Montorng Conference, Houston, TX.

K., 1992, "lnspection Technologies for a Wide Range of Pipeline Defects," Pipeline Pgging &Inspectioll Tedmology Conference, Houston, TX.

D.L, et al. 1959, Handbook of Gas Engneering, McGraw HiII Book Co., New York, NY.P., and Mohitpour M., 1987. "Non-Newtonian Liquid Pipeline Design and Simulation Using

Microcomputers," Prac. ETCE Conference, New Orleans, LA.. PD-Vol 3, pp. 73-18.c.8., 1958, Hydraulics for Pipelines, Oilden Publishing Co., Houston, TX.

1977, "Sorne Technical and Economic Aspects of High Pressure, Long Distance, LargeDiameter Gas Transmission Pipelines." Prac. 16th AlRAPT Conference, University of Colorado,Boulder, Colorado.

. 1987, "A Guideline Manual for Design 01' Hydrogen Pipeline Systems," NOVA Internal Report,Calgary, Alberta, Canada._ . _ , 1991, "Tempcrature Computaton in Fluid Iransmission Pipelines," Prac. ASME ETCECOllference, Volume 34, Pipeline Engineering, pp. 78- 84.

M., and Kung P., 1986, "Gas Pipeline Hydraulics Design and Simulation: A MicrocomputerApplication," Proc. Conference Society for Computer Simulation (SCl), San Diego, CA.

M., and McManus. M.. 1995, "Pipeline System Design, Construction and OperationRationalization," Prac. ASME 14th OMAE Conference, Copcnhagen, Denmark, VoL V, PipelineTcchnology, pp. 459-467.

L. E, 1944, "Fricton Factors for Pipe Flow," Imnsaction ASME, 66, p. 671.J. M., 1977, Elements of Pipeline Enginecring, Canuck Enginccring Ud., unpublishcd Training

Course \'1aterial... Ronsky, D., and McManus, M., 1992, "Risk Assessment an Integrity

Managemcnt Tool," Pipeline Risk Assessment, Rehabilitaton and Repar Con(erence, Houston, TX.R. L, Coutts, R., 1991, "Risk Assessment and Inspection for Structural Integrity

Managcment," PiPeline Pigging & lnspection Technology Conference, Houston, IX .V. R., and Mowll, R. T. L., 1982, "How to Predict Flow of Viscous Crude," Pipeline Industry.

F., Mohitpour, M., SL J. Price, J., Porter J., and Ieskey, W. F., 1988, "Pipeline Integrity Analysis andMonitoring Systems Show Defomlation Behaviour," Praceedings o( the 7th Annual ASME-OMAEConference, Volume V, Houston, IX , pp. 1 158.

elements of pipeline design

Documents