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Management of Change (MOC) Process Changes in the project scope, or revisions to drawingsand designs, arecommon duringconstruction.It is important for these changes to be properly understood andtracked,withtheir cost andscheduleimpactsapprovedandrecorded by appropriate authorities prior to implementation. This processis known as change management orthe management of change (MOC) process. Shop Drawings During fabrication activity, the fabricators adddetails totheoriginal engineering drawings and increase their scale to facilitate fabrication anddimensionalaccuracy.Theserenditionsareknown as shop drawings. As-Built Drawings Some engineering drawingspreparedby the engineering contractor are changedand/or modified inthefield to accommodate any deviationsfrom the originalconstruction plans. All such revisions are assigneda successiverevision number. Revised drawingsarecalledas-builtdrawingsor simply “as built.”

Shop Inspection Owners/clients typically retain qualified individuals who are trained to inspectcertain items being fabricated along withthe processes being usedin a fabrication shop.

These persons continuouslyinspect some orallof the items before they areshipped. This activity isknownas shop inspection. Any person or organization, which maybe contractedto supply equipment or materialsto be used in construction orprojectexecution,is known asa vendor. Logistics The process(subject/specialty) of planning andarrangingto deliver goods fromthe place of origin (manufacturingor fabricationshop,sales organization, factory, etc..) to a place of use/utilization (inthis case the construction site) is knownas logistics.Logisticsis a vast and complicatedfunction/discipline that can positively impact theproject scheduleandcosts if it is handled effectivelyby avigilantlogistics manager. Occupational Safety and Health Administration (OSHA) The US OccupationalSafety and HealthAdministration (OSHA) isa federal agency,which sets guidelines forworkplaceenvironments,and overseesconstruction and manufacturingindustries to makesurethat safe practices areestablished to protect thehealthandsafety of workers.TheHS&E component ofa project functions within the OSHAguidelines. Environmental Protection Agency(EPA) The US Environmental Protection Agency (EPA)is a federal entity thatoversees, and sets standards for, all businessesandindividuals interacting with the environment during construction oroperationalactivities. EPA’s objective isto ensure that all activities are geared toward keeping the environment (air, water,and earth)safeandclean. This agency also hasthe power to imposepenalties for noncompliance with environmental regulations or violationof

environmental laws.

Progress Payment Aprogress payment is apartial payment tothe contractor for a specific task performedor for a portion of the assigned totalworkthathas been accomplished. The metrics usedto evaluate/assess the amountof work to be accomplished are agreeduponbetween the ownerandthe contractor inthe contract documents. Nonetheless, it issometimes difficultto accuratelyassess the amount of workaccomplished, whichcan lead to conflict between theowner/client,project management team, andcontractor. Change Orders Whenever there is achange in scope, whichleadsto an increase or decrease in theprojectcost/budget ora change in the schedule,the contractor isexpectedto file anexplanationalongwitha request for owner/client approval priorto starting thework.Thisdocumentation is known as a changeorder. In casethe contractor starts theworkbeforethe change order is approved, the owner canrefuse to pay for it, which can lead to litigation. Therefore, all changes,whetheroriginating from theowners/clients or thecontractor,must be agreedto and signedbeforethe start ofworkin the field. Mechanical Completion The stagein the life of a construction project, when all equipmentand appurtenances are in place, duly fitted, shop-tested, andreadyforpre-commissioning, is knownas mechanicalcompletion. Sometimes the terms “mechanical completion” and “pre-commissioning” are usedinterchangeably, especially when the scope of both activities isintegratedbased on some compelling reason. Sucha situationoftenoccursin pipeline projects. Pre-Commissioning Generally, allmechanical, electrical, and control equipmentis shop-tested,and

all pipeandfittingsarehydro-tested forleaks and weld strengths, beforetransporting them tothe construction site.

Once all the pieces are in place and are connected as required,and the projecthas reached the mechanical completion stage describedabove,the operational functionalityof entire units, sections,or systems of the facility/assetcanbe tested. Such components may involve multiplekindsof equipmentthat collectively are expected to perform a specific function or produce an intermediateproduct that is integral to theperformance ofthecompletefacility/asset.The activities described here areknownas pre-commissioning. Commissioning Commissioning is the final stageof certifyingthatthe project is complete in allrespects and can produce the intendedproduct as definedin the project scopeand specifications. This isthestage when allequipment andappurtenanceshave beenindividually tested andcertified bythefabricators/manufacturersin their respective shops,withallindividualunits/systems having beentestedduringthe pre-commissioning stage describedabove. Essentially, commissioning of the complete facility/asset encompasses testing andverifyingallsystems for their operability. Forexample, commissioning of anoil refinery involvesfeedingtheraw material (unrefined crude) directlyintothe crackingunitat the appropriatejunctureandenergizing all equipmentand systemsto yield the expected amount of refined oil/gasoline ofspecifiedquality. If everything functions as expected and meets the specifications andthedesign requirements, then the facility is saidto have been commissioned. This is the final stage intechnical acceptanceof an asset, and at this point, the contractor isreadyto give the owner a fullyfunctionalfacility. Hand-Over Process Once commissioning is complete and asset functionality isverifiedby the

owners/sponsors and vendors, a formal handover ofthe facility is performedby the

contractor to the owner/client. This steppromptstheformal closure of thecontract that wassignedat the beginningof the project between the owner/client and the contractor. At this stage, the contractorshouldbe fully paid unless, of course, there are any ongoing disagreements about change orders requiring resolution.


Types of Construction Construction is not just digging holes in the ground, pouring concrete, and erecting steel. While thesethree activitiesarea major part of most construction work, construction projects arequitecomplexandrequire a full range of planning,applicationof technical skills andinclude QA/QC activities and HS&Emonitoring. Construction could be in water,e.g., offshore platform, terminals oron dry land,e.g.,high-rise building or petrochemical refinery, or a highwaybridge. Therefore,the construction projects whicharediscussed in this ARTICLE (OF BHADANIS INSTITUTE) are categorized asfollows:

Based on ProjectLocation: Offshore Onshore

Based on Usageof Facilities: Industrial Commercial Residential Public infrastructure Offshore Construction Offshore construction is very differentfromonshore construction in eachand everyway,i.e., size, shape, techniquesof construction, materials, equipment, environment,risks and especiallythe cost. It isimportant tounderstandwhyit is so. And forthisreason, the authorhasdevoted this chapter on identifying the various elements of three major offshore project types:

Offshore platforms, pipelinesand terminals are installations, structures and facilities in a marine environment forgenerating andtransmitting power aswell asfordrilling, collecting, processing and transportingoil,gas, water, LNG, and othersuchcommodities. All three of these items (platforms, pipelines, and terminals)areindependent andstand-alone subjects andspecialties, inengineering aswellas in construction. Thevariousconstruction,fabrication, andinstallationtechniquesforall three ofthese specialties are totally different.Therefore,to keep thereaderfocused on onesubject at atime, all three of these subjects shall be discussed in three different sections in thisARTICLE (OF BHADANIS INSTITUTE), starting with offshore platforms; offshore pipelines andfollowedby shipping and marine terminals. Byusagecategory,all three of the aboveoffshoreprojectsfallunderthe “Industrial” category. Some may consider the terminals as commercialstructures.The residential quarters built offshore for the workers can also be categorized in residential aswell as industrialcategories. Public infrastructure may constitutebridgesoverthe water bodies,etc.But these are not much different than terminals, in terms of construction techniques.Commercialinfrastructures mayconstitute some hotelswhich may be built in waterpartially.

But the construction and constructiontechniquesforthese structures areno different than whatwouldbe used in terminal construction. These threecategories are discussed at length in the following chapters devotedto “Offshore Construction”, should be sufficient tointroduce the readers to offshoreconstruction.

Chapter 4

Offshore Construction Three main topics of offshore construction will be discussed in the followingpages: offshore platforms,pipelines &ShippingTerminals. A. OffshorePlatforms Offshore platforms are complex, costly structuresbuiltoffshoreto producehydrocarbons (oil & gas) from under the sea. The general term “platform”is usedcasuallyto refer to any facility offshore. Thesefacilities areof various typesas discussedbelow.Nowthe question is, which oneof these various types offacilities isappropriate fora particularproject? This selection processis based onmanyengineering and construction criteria and is briefly discussed belowin the “Concept Development” stage of a givenproject. Offshore platforms are generally built withsteeland or concrete materials. Before we delve into the details ofwhatis a “fixedplatform”or a “floating platform”; it is important to define whatis a “platform”. Offshore platforms are generally self-contained and self-supporting facilities with all the equipment and personnel,required with fueland power, and lodgingand boarding facilities for the workers. Most of the platform facilities are equipped with heliports for transportingpersonnel and bringing inrequiredamenities. These facilities generally havetwo to three floors,dependingon the purposeof the facility.

There are a lot ofhydrocarbons beneath the oceanfloor. However, extraction of hydrocarbons requires much more than just a platform facility. It is a multi-faceted exercise, andinvolvesvarious activities as briefly delineatedbelow: Locating and ascertaining the hydrocarbon field (reservoir)underthe sea. Drilling into the oceanfloorto reach and tap this reservoir. Installing a technologicallycomplexmechanical device called a“ChristmasTree” over the drilled hole, to control pressure and flow ofhydrocarbonfluids flowing from the reservoir under theseafloor into apipelinesystem. Installing subsea pipeline system for transportation of thesehydrocarbons via pipeline to a hydrocarbon processing facility on another platform or on land. Power generation for offshore use; and Installing compression and/or pumping facilities for generatingextrapressure to speed up gasandliquids transfer via pipelines, etc. Concept Development In the concept developmentstage of a project,it may not be knownas to whattype of asupport structure would be erected offshore to house and support therequired platform facilities. Finaldecisionon selectingthetype of structureis madegenerallyin the FEED (Front End EngineeringandDesign) stage of the project, especially in thecaseof a “fixed” platform. The decisionof what type of platform structure is going tobe built is based onmany considerations, including: Purpose of the platform Fabrication,

Transportation, Cost,

Site characteristics, and Constructability The followingis a brief discussionon the types of platforms based in engineering designconsiderations; andthe various types of offshore facilities, structuresand their maincomponents⁸.

Types of Platforms Based on Engineering Design Concepts Fixed platforms Semi-submersibles Spars Tension Leg Platforms (TLPs) Floating production Storage and Offloading (FPSOs) Floating oil and gas platforms– semi-submersibles,spars, TLPs, & FPSOs. B Based on Platform Support Configuration In the case of an offshore platform, there aremany choices available as for as thetype of platform support systems areconcerned.Suchas:

C Based on Platform Use/Functionality Abrief descriptionof these platformsbasedon provided in the following paragraphs.Oncean oil/gas reservoiris identified and mappedunder theseafloor,a drillingplatformis built over it and used fordrilling wells torecover oil/gas. These drilling platforms are generally two-to three-floor structures. These are designed to carry very heavy loads as much as 800–1,000pounds per square foot (psf) ormore.Thefloor structure isdesignedto accommodate impact loads. These aresometimes temporary structures and are removedaftercompletion ofthedrillingfunction. Aprocess platform is meant for processingthe crude oil and gas as they receive from different wells via pipelines.

Processing of hydrocarbon fluids isperformedto separate unwanted impurities,such as water, solids, sandandgases from crudeoilor gas and then transport the processedhydrocarbons to shoreforstorage or distribution orto refineries for further processing. Living-quarters platform facilitiesarebuilt for workersto reside onsite for theduration of theiroffshore shifts. These shifts generally last twoto four weeks.These facilitiesarefully equipped withall basic needs and necessities (sleeping, eating, entertainmentandexercise equipment) that a person normally requires.These facilitiesareoften times installed on work platforms or connectedvia a bridge. And sometimes they are built totallyseparatefromwork platforms; andin such cases,workerscommuteto the workplatforms byhelicoptersandor boats. Nothing workswithout electric power; be it equipment,kitchen,or entertainmentequipment. If the platform is relatively closeto land andpowerstation,power cablescanbe laid under water, butit is very costly. Therefore, power generation platforms arebuiltfor producing power usingdieselandor gas-powered turbines.And then poweris transmitted to otherplatforms,suchas the process platform and or compression platform via underwater cables. Similarly, Compression Platformis where Compressors are installed to giveneeded boost to gas pipelines as required for long-haul transportation. These areeitherpowered by power from the power platform or self-supported bypower generated onthesame platform. Generally, the hydrocarbons are undera lot of pressure while coming out ofthe reservoir. However, overtime, the pressure in reservoirdeclines and hydrocarbons need to be forced out ofthereservoir. Therefore,artificial pressureis created by forcing

or injectinggasor water into the reservoir to force out the hydrocarbons.Platform’s facilities used for this purpose are knownas injection platforms.

Pipeline platform is simply a facility for the gatheringof various pipelinesto go through some additional processing. The combinedhydrocarbons are transportedto shore viaan export pipeline or a vessel.

Anatomy of an Offshore Platform Structure Physically, an offshore platform consists of essentiallythreemajor components, see figure 4-1 below: Top sides Jacket Anchorage/foundation

TopSide/Deck Jacket Anchorage Sea Floor Fig. 4-1 Main Componentsof an offshore platform All three components are designed and fabricated generally independently and have very different design criteria, materials aswellas constructionmethodologies.

Let us brieflydiscuss the progressionof all three parts delineatedabove from design to fabrication to installation. Essentially all three stages need construction management involvementduringthe concept development and thedesignphase, as you will seebelow . Top Sides This is the working spacecreatedon top of an actual platform that youseeabove thewaterlevel.It houses and supports the required equipment andfacilities,relating to workas well as workers. Top Sidesoften consists of more than onefloor.It is generally square or rectangular,dependingon its function or the type ofworkthat is tobe performedon this platform. Generally, all top sides structures are fabricated onshorein fabrication shops and aresupervisedby constructionmanagement professionals to make sure that theirsizes, weld qualityandtransportability meets or exceeds the specifiedfabrication project standards/specifications. Once the fabricationis complete, all requisiteequipment is installed ontheit. And when all required testing iscompleted satisfactorily,arrangementsaremade to transport the Top Sides structure tothe construction site. This is a big operation andwillbe discussedin the transportation section below. Jacket Jacket is the support structure onwhichthe Topsides rests. This is the part ofthe offshore platform that keepsthetopsides of the platform secure above water. Itis

the part that is partly above water and partly (majority)underwater and is generally foundedon the sea floor.This is madeof steel or concrete or a combination ofboth.Andit comes in many shapesand sizes.

Foundation & Anchorage The followingpicture/rendering shows various configurations ofsupportingplatform facilities offshore. While eachof these supporting systems is acceptable, each isandselected as appropriatefor distinct designconditions¹¹.

Fig. 4-2 Varioustypesof offshore Oil &Gas facilities U.S. Department See legendbelow:

Legend for Fig. 4.2 1, 2) Conventionalfixed platforms (Shell’sBullwinkle in1991at 412 m/1,353ft Gulfof Mexico) 3) Compliant tower(ChevronTexaco’s Petronius in 1998at 534 m /1,754 ftGOM); 4, 5) Verticallymooredtension leg andmini-tension legplatform(ConocoPhillips’Magnolia in 2004 1,425 m/4,674 ftGOM); 6) Spar (Dominion’s Devils Tower in 2004, 1,710 m/5,610ft GOM); 7,8) Semi-submersibles (Shell’s NaKika in 2003,1920m/6,300 ft GOM); 9) Floatingproduction,storage,andoffloading facility ( 2005, 1,345 m/4,429 ftBrazil); 10) Subsea completionandtie-back to hostfacility (Shell’sCoulomb tie toNaKika 2004, 2,307 m/ 7,570 ft). Fixed Platforms

Fixed platforms areeconomically feasible for installation in water depths up to1,000 feet. These canbe single leg supported or multi-legged. Term “Leg” is usedto define the main support membersof the jacket structure, whichsupportsthe actual platform topsides. Platform Jacket legs are generallymade of tubular steel, andbracingcouldbe tubular and or otherstructural shapes.Dependinguponthe design specificationsand requirements, the legs are also used for carryingthe various cables and conduitscarrying power,hydraulic fluids, and chemical feed systems.Whenthe legs are ofverylargediameter (5to 20 ft. or larger) pipes,these are sometimes used for storing hydrocarbonsproducedin the field.

Such facilities are built aspermanentstructuresfor the life ofthe project, 25-to-35-year duration, and as such are immobile and hence their name(fig.4-3).

Fig. 4-3 Multi-Leg Platform Concrete Jacket Concrete jackets cannot be used in deep waters, because ofdifficulty in buildingcofferdamsto build them (fig. 4-4). Concrete also needs to have several types ofadditives to make it resistant to chlorides,freezeand thaw and imperviousto water,especially because concrete jacket structures are often used for oil storageduring production in additionto supportingthe super-structures or decks. Often,these structures are built onshore and floated to the platform location.

Fig. 4-4 Four-Legged Platform (Concrete) Single-leg Platform(Monopod) Single leg Jackets can support multi-deck platforms. These types ofstructures arealsoknown as “Monopod”or single-leg platforms (fig.4-5).Monopods can be made ofeither steel or of concrete ora combinationof both materials. Thesetypes of jackets are preferred inrelatively shallow waters, especially where iceloads are expected onthe jacket. The shape of monopod is generally truncatedcone to avoid frozen(icebondedto the monopod sides) ice loads. These monopod jackets are used for storing hydrocarbons (fig. 4-6) and other materials as deemed necessary bytheoperatingengineers.Generally,the “jacket” structuresare only required for “fixed” platforms; “Gravity Based” structures,“Spars” and “Compliant Towers” (seedefinitions below).Othertypesof platforms aresupportedusingtotallydifferent conceptsand

methodologies, as discussed later in this chapter.

Fig. 4-5 Single Leg Platform/Monopod

Fig. 4-6 Schematicof a SingleLeg Platform/Monopod Interesting, News Tagged With: Hebron project, offshore oil and gas,

Gravity-based Structure (GBS) Gravity-based structures are those platformswhich rely on their own weight forstability of theplatform against theforcesof nature, i.e., waves, winds, storms,etc.These structures can either be steel or concrete and are usually anchored directly onto the seabed. These structures(fig. 4-7), when completed,willbe transported totheconstruction site and installedunderwater,restingon the sea bottom¹ .

Fig 4-7 GravityPlatform Jacket

Tension leg platform (TLP) Topsides of Tensionlegplatforms (TLP) is designed such that it floatson water whiletied to a foundationon the sea floor by flexible metallic tensioners (fig. 4-8).In order to stabilize the platformat one location, it is moored(tieddown)to a subsea foundation system with structuralmembersknownas “tendons”. TLPs are used inwaterdepthsup to about 2,000 m(6,600ft). This designof a TLP includes four air-filled columnsforming a square. These columnsare supportedand connected by pontoons. Modern TLP designscompriseof a ring pontoon connecting fourcolumns¹ .

Fig. 4-8 TensionLeg Platform -TLP

Spar Platforms Spars are unique structuresin that that these structuresaremoored to theseabed like TLPs. ASpar hasa large counterweight at thebottom, andtherefore,doesnot depend on the mooringto hold it upright.ASpar can bemovedhorizontally from one locationto another by just adjusting the mooring line tension. Spars are generallycome in three configurations¹ , as discussed below: 1. “Conventional” Spar It is a one-piece cylindrical hull asshownbelow in fig. 4-9 below theDeck

Fig. 4-9 Spar Platform

2.The “Truss Spar” As the name implies, atruss structure constitutes themiddle section of this Spar. This truss is connectedto a buoy (a buoyant tank) atthe top, popularly knownas a “Hard Tank”. And in turn it isattachedto a ballast filled tank at the bottom for anchorage. 3.The “Cell Spar” The Cell Spar is built from multiplevertical cylinders. Similar to fig. 4-9 above. Compliant Towers Acompliant tower (CT) is a fixed rig structure, andconsistsof narrow,flexible(compliant) towers, asseenin fig.4-10 below. These flexible towers are supportedon a pile foundation. Compliant towers aredesignedto sustain significant lateral deflections andforcesand are typically usedin water depths rangingfrom1,500 to 3,000 ft (450 to 900m). As compared with floatingsystems, such astension-legplatforms andSpars,the production risers in this type of platforms are subjectedto less environmental loads, and consequently,require less flexibility¹ .

Fig. 4-10 ACompliant Tower -BBLT, (Courtesy: Google)

Floating Production Systems The main floating production systemsareFSU, FSO andFPSO. AnFPSOis an acronym for “Floating Production, Storage, andOffloading”. FPSOsconsist oflarge mono-hull structures, generally shaped like aship,and equipped withhydrocarbon processing facilities. These vesselsare moored to alocationfor extendedperiodsandare supplied oilor gas for processing andstorage. One variant of the FPSO is called FSO, “FloatingStorage and Offloading". Anotheroneis known as FSU, “FloatingStorage Unit”, andis used exclusivelyfor storage purposes. Allthree of these areknownas “Floating Production Systems”. See fig. 4-11 below.FPSOs are for offshore regions wherethere are nomeansavailable to process, ortransport recovered hydrocarbons immediately.They are generally fabricated in onshore facilities and floatedto a desired location and installed. Often, oiltankers can beconverted into FSU,FSOand FPSOs instead of building new vessels¹¹.

Fig. 4-11 AnFPSO in operation LNG (liquified natural gas)is a clean fuel,andtherefore in great demand.Therefore, offshore gas fields are installing“Floating Liquid Natural Gas”(“FLNG”) vessels. These FLNG vesselsarelike an FPSOin operation and appearance. An FPSO and FLNG allows full-scale processing, with almost noreal estate and minimal environmental impact¹¹. See fig.4-12,a schematicof an offshore operation usingan FPSO or FLNG.

Fig. 4-12 Schematicof an FPSO (Wikipedia) Semi-submersible Platform ASemi-submersible platform (fig.4-13)is supported oncolumns and pontoonswith buoyancy. The structure must bekeptupright and afloat,and therefore, anchored using moorings during operation. Semi-submersible platforms canbe movedfromplace to place, andballastadjusted.However,during the drillingoperations, these vesselsareheld precisely overthe drilling location byusinga dynamic positioningsystem/mechanism. Semi-submersiblescan be usedin waterdepthsranging firm 60to 3,000 m(200to 10,000 ft)¹¹.

Fig. 4-13 Semi-submersible platform schematic Drill Ships As the name indicates,a drillship isa vessel (fig. 4-14) which is usedfordrillingoil and gas wellsunderwater. It hasspecialconstruction features, suchas a tower in the middle and drilling equipment.In order to keep thesedrill-shipsstationary on the well locationwhiledrilling, thedrillship isoutfitted with adynamic positioning system tocompensate for motiondueto wave action.

Fig. 4-14 Jack-up Drilling Rigs Jack-up drillingrigs are mobile units which canbe relocatedandadjusted to any elevation abovethe sea level with alevelling mechanism(fig.4-14). Alsoknown asMODUs(Mobile Offshore Drilling Units), they are typically used in water depthsas much as 200 m/600feet.

Platform Anchrage/Foundation This is the third part ofan “Offshore Platform” system. FixedPlatformsaregenerally founded on piled foundations.CompliantTowers,TLPsandSpars also need foundations/anchors. Criteria for pile size, pilelength and material, and number of piles required are determined basedon the geotechnicalpropertiesof the ocean floor.

ASemi-submersible is much like aTLP,except that it is tied to a foundation for vertical stability.It does need horizontal stabilizing mooring lines andor “dynamic positioning” system to keeptherig at a stationarypositionon a specific point orlocation[explainedearlier]. An FSO and FPSO, as well as drilling vessels, essentially use the same system for stabilization asthe semi-submersible described above. Dynamic Positioning system consists of thrusters/jets and control systemswhichsense the movement of thevessel,andautomatically fire water jets to controlmovement of the vessel. And consequently, the vessel stays stationary at a particular point, asperthe well coordinates input inthe system. Pile Installation Generally, the jacket is supportedon pile foundationsin the ocean. Therefore, pile driving mathematical analysis needsto be done before theactualinstallationprocess. Marine pile lifting analysis Pile structure analysis and design Hammer selection Pile drivability analysis Pile free-standing analysis Pile stabbing tolerance analysis Pile grouting design procedure development

Details of the above items are outof scope of this ARTICLE (OF BHADANIS INSTITUTE). The reader can find theseitems in engineeringdesignARTICLE (OF BHADANIS INSTITUTE)s on offshore pile foundations.


Fabrication & Transportation: Fabrication and testing of many offshore facilities is carriedoutonshore. And it isa successfullytried strategy from economic andsafetypointsof view.The fabricated part oftheoffshore facility is then transported/towedto the installation site by floating on its own buoyancy or ona barge. Thereafter, thefabricated structure is lifted byoffshore cranes and installed in place. The sizeof offshore lifts, however,can be reduced by making the construction modular. Amodule is a part of the whole structure, which canbe independentlyfabricated and then integrated into the main facility. Therefore, each module can befabricatedonshore and thenliftedinto place using a crane vessel. Offshore construction includes new construction as well as the repair of existingoffshorestructures.One key factor inoffshoreconstructionis the weatherwindow, which defines periodsof relativelylight weather for construction offshore. Amajority of offshore tasks are accomplishedby using ROVs (Remotely Operated Vehicles), which are essentiallyconstruction robots, especiallyif the construction isin deeper waters.¹¹

Towing & Load-out Once modularfabrication iscomplete, thefollowingitems are prepared to safely transport thestructuresusingvessels or otherappropriatemethods to reach the construction site. These items arelisted for the constructionmanagementprofessional to realize thattransportation planning ofa jacket is by itself a major undertaking. Detailed explanation of these items is out of scopeof this ARTICLE (OF BHADANIS INSTITUTE).

Jacket In-Place Design Configuration design Strength analysis and design Seismic analysis and design Pushover analysis Impact analysis Foundation pile design Major connection design Miscellaneous steel design Fabrication Support Jacket Load-Outand Installation Support Load-out Load-out method Load-out ballast analysis Structural analysis of jacket and barge Stability analysis

On-site technical support and supervision Transportation (Seefig.15below) Tow routeplanning Tow routeenvironmentcriteria

Marine transportanalysisanddesign Structural analysis and design (jacketandsea-fastening)

Fig. 4-15 APlatform Jacket beingTowed

Jacket LaunchOperation This operationcovers unloading and lowering of the jacket into the ocean, and place it at its predeterminedlocation on the ocean floor. There are various steps tobe accomplishedbeforethe actual launch ofa jacket; and calculationsarean important part of it, as describedbriefly below Marine & Structural lift analysis anddesign Jacket flotation analysis anddesign Jacket upending analysisanddesign

Upending structure strengthverification Jacket loweringanalysis Pile Stabbing Structural analysis

Topsides Installation There are three methods of topsidesinstallation:Single-lift,Multi-lift andFloat over. Single-lift Method: This method is used when total structure is fabricated, transported andthenliftedand installed in place.Thisstructure could bean entire deck of a platform or amodule. Sometimes, more than one crane barge is used to lift the structure, especially if theload is toobigforone crane, and to keep the load stable during installation. See fig. 4-16 for “single lift” module installation. This method is applicableto relatively small structural modules which arefabricated as a completeunit,withall the utilities and equipmentrequiredforthe whole module to function. After this module islifted and put inits designated place atop the jacket, power and utilities are connected tomakeit operational.

Fig. 4-16 APlatform module beingliftedin a singlelift atop ajacket. ((Offshore Trinidad: Multi-Lift Method This method is most prevalenton large platformsstructures, where total weightof the topside (deck)or jacket structureexceedsthecrane lifting capacity.Therefore, the modular construction is adoptedandeach of the modules are transported andthenliftedin place one by one.See fig. 4-17.

Fig. 4-17 APlatform module beingliftedin (multi-lift) atop a platformdeck. Float Over Method This is an entirely differentconcept for lifting and installinga platform deck atop thejacket.In this method, a flat-bed barge is used to bring the deckstructureto thesite.Elevation oftopof jacket isdesignedpreciselyto stay below the ocean level duringhightide. At thetime of high tide, thedeckstructureis floated over thejacketstructure,and held precisely above thejacket top locationsdesignedto receive thedeckstructure. As soonas the tide startsto ebb, the jacket bottom slotsdesignedto connect with the jacket top,slidesoverthe jacket columns andthe operation is over. As you can imagine, it takesa lot of precision in fabricationas well as during installation in a float over method. Aminisculemistake in dimensions can make thewholepreparation and hardworkunsuccessful.

Chapter 5

OFFSHORE PIPELINES Once hydrocarbonproduction starts at aplatform,it is only possible to store limited amounts offshore because ofphysical space limitations. Hence, additionalmeans must exist totransportthehydrocarbons safely andeconomicallyto other locations.The only feasibleoptionsfordoing so are transportation via ships/tankers, transportation via pipelines,or some combination ofboth.Thischapter deals with pipeline transportation of hydrocarbons and the many facets of pipeline constructionthatmustbe considered in offshore marine settings. Pipelines In the context of the pipelinesassociatedwith offshore platform structures andoperations, there are two types ofpipelinesto consider: Flow lines: Pipelines bringing fluids fromthe production wells to the platform areknownas “flow-lines”. Pipelines: Whereas pipelines transporting fluids from a platform to a storageonshore or FPSO are termed as “pipelines”. In essence, there is no difference in the engineering design and constructionmethodology. Both areengineeredto withstand certain amount ofinternal pressure,externalpressure,andbending, twisting etc., due to other external loads suchas,waves, dropped objects, buoyancy,earthquakes, andso on.¹²

Size Pipelines can be as small as4 in in diameter toalmostanydiameter,as long as it can be rolled into apipeshape, and a pipe-lay vessel is capable of laying the pipe is

available in the market. It is, however,difficult to findvessels capable ofinstalling pipelines larger than 72 in in diameter as of 2021.

Fabrication Offshore pipelines are generally made from various types of steel, depending upon the properties ofthe fluids being transported.The cost ofmaterials isjust oneaspectof the totalcostof pipelines. Installation cost generallyfarexceeds the material cost. Sometimes, the line pipe has to beprotectedfrom the corrosiveingredients in the fluids flowing in the pipeline by coating or even by claddinginternally. This addsto the material fabricationcost. In addition, buoyant forcesactingon the pipeline while lying on the sea floor must be overcome to keepthe pipeline from floating. Andforthis reason, generally linepipeis concrete coated toincreaseitsweight. The claddingprocessmustensure that two metals are inseparableto eliminatewater seepage in-between. Any separationof the two materials canleadto corrosionandthe only mitigationis pipeline replacement.

Pipe-in-Pipe There is another factor that sometimes dictates thecross-sectional geometry ofthe line pipe, and consequently,itsfabrication. Thissituation arises whenthe fluidsbeingtransportedin the pipeline are prone to gelling or crystallization. Thisphenomenonoccurswhen the contentsinsidethepipelinestartlosingheatto the sea water surrounding the pipeline.Thereareseveral methods availablefor insulating the pipeline or add heat into the fluid inside the pipeline to counter thisproblem.However,many a timesnoneof these methods help and a “pipe-in-pipe”or “PIP” cross-sectionis developedfor the pipelineandthe annulus is filled with an insulating material. This double-pipesectionis the ultimate solution forpreventingheatloss in subsea pipelines.Thus,it becomes muchcostlier than aconventionalpipeline fabricated ofsinglepipe,andtakes more time and special expertise to engineer, fabricate andinstall it.

Similar to the abovecaseof cladded pipe,thereis zero tolerance foranyflaws in the fabrication of PIP segments.Any failure/leakage of aPIP pipelinesleads to total abandonmentof the existingpipelineandreplacement with a new one, resulting indisastrousfinancial lossesby shutting down operations, plus additionalcosts for pipelinereplacement¹³.

Corrosion Protection There is the possibility of internal as well as external corrosion. The line pipe has to beprotectedfrom the corrosive ingredients in the fluids flowing in thepipeline by internalcoatings or cladding. Then there is outside corrosion and salinity ofwater,which can reduce pipelinethickness,andthereby reducing theMAOP(Maximum Allowable Operating Pressure)forthe pipeline. Thiscondition can leadto leaks and even rupture ofthepipeline,creatingan environmental disaster, lossof production,and most of all, costly underwater repairs,or even worse abandonment of the pipeline.Therefore, all pipelines are given a FBE (Fusion Bonded Epoxy) coating on the outer surface. In addition,a “Cathodic Protection”systemis designed tocontrolthe flow ofelectric current betweenthe metal and the sea water.This is accomplished by attaching“anodes” to the pipe atcertain intervals. Anodes are essentiallymetallic rings madeof special alloysandare attached to thelinepipeat distances calculated by the design engineer, based on theenvironmental conditions and thesizeof the pipe. All of these operationsmay or may not be accomplishedat the samefacility. But the pipe is not ready until andunless all necessarysteps are completed appropriately. Mistakes arenoteasilymendable in offshoreenvironment.When it becomes necessary tofixa mistake intheocean, it isas much as 10 to100times the original cost. This willobviously have a negative impact on the projectschedule. Once all these operationsareover and the pipe sections (which are generallyof 20-ftlengthsandare popularly called “Joints”. Dependingon the pipe lay and transportation

methods, these joints can be as much as40 ft long), are ready forshipmentto theconstruction site forinstallation.¹²

Installation of OffshorePipelines Installation is the costliest part oftheoffshore pipeline construction. Total cost variesaccordingto water depth, i.e.,the deeper the water, the more complicated and costly pipeline installation tends tobe.Even the construction methods andthe type of installation vessel that is neededvarydepending on waterdepth(moredetailsprovided below). Installation Techniques There are three primary methods of laying pipeline in offshore marineenvironments: reel-lay, S-lay, and J-lay¹¹.

Reel-lay The reel-lay methodinvolves the use of specially built vesselsequippedwithreels that have an appearancesimilar to thereelsusedfor maskingtape,sewing thread, or garden hoses.Thedifference is that these reels are made of metal and areobviouslymuchlarger, on the orderof hundreds of feet in diameter. Twenty-foot-long line pipe sections arewelded together to produce pipelinesegments that are hundreds offeetin length, which arethen wrapped/rolled around the reels like awireor thread. Most vessels carry as many as three reels, exceptforEMAS AMC’s Lewek Constellation,whichcarriesfivereels. Having more reels translates to a shorter pipelay laytime, and consequently, more costsavings. The reelsof pipe are loadedontoa lay vessel (a pipelaying ship or barge) andthe vesselthentravelsto the constructionsite and startslayingpipeunder the expertdirection of the construction management staff. The vesselkeepson layingpipeuntilall the reelsaredepleted. Thereafter, it returns tothefabrication shop, reloads, returns to

the construction site,and resumes the pipelaying operation. This processis repeated asmanytimes as neededuntilthepipelayingoperationis successfully completed. Figure 5-1 illustrates areel-layvesseland pipelaying operation.

Fig. 5-1 Reel Lay Vessel Reel-lay is a very efficientandcost-effective method forinstalling offshore pipelines, but it can only be used with pipediameters 18in.or less due to strain build up in thepipeduringthe reeling operation. Useof the reel-lay method is alsolimited towaterdepthslessthan approximately 5,000 ft, depending on pipe dimensions.

S-Lay S-lay (also known as“conventional” lay) isthesecond method oflayingan offshore pipeline, andit is the most used method in the industry. Inthis method, sections of pipe areloaded on apipelaying vesselandtransported to theconstruction site. Sections are weldedtogether in sequence on the vessel and the assembled string/span iseasedoff

the sternviaa sloping rampknownas a stinger,a steel structurewith rollers analogous to a firing line protruding into the water.As the vessel moves forward,the string proceeds downward into the water forming an “S” shape as it touchesthe ocean floor.The stinger, which islocated at the end of the ramp, supports thepipeline span to control curvatureof the upper section (overbend)and to prevent undesirable deflections, thereby keeping stressesin the assembled pipeline within allowable limits. Stinger lengthdependson water depth and the submerged weight ofthepipeline string. Tensioners, “caterpillar-liketracks”located on the ramp grip the pipe to hold the suspendedlength in placeand control curvature ofthelower section (sagbend). The S-laymethodcanbe used to install pipelineshavingvarious sizes. Thereare nolimitations to pipeline diameter and length as long asthe tension can be controlled andstressesin pipe during the lay operationare kept within thecode limits. The S-laymethodpermitswelding,inspections,and field jointapplications tobe performedat the same time with minimum onshore support requirementsafter installation has begun. Pipelaying speedis very good,evenfor large-diameterpipelines -- typically twoto six km/day --however,the rate does depend onseabed topography and water depth. Tension capacitylimitationsrestrict S-layoperations to waterdepthsof about10,000ft. Fig 5-2 illustratesan S-lay vessel and pipelayingoperation.

Fig. 5-2. S-layvessel during apipelaying operation

J-Lay Loading and transportation of pipe to the construction site isessentially identicalfor the S-lay andJ-laymethods.Similarly,as in the S-lay scenario, pipe sections are welded together in sequence on the vessel andtheassembled string/span is inserted intothe water.Beyondthis, the two methods are considerablydifferent. Unlike the S-lay method, the pipelayingvesselused in a J-lay operationdoes not have an extended stinger to help ease the pipeline into the water at a comfortable angle.

Instead, the pipeline is lowered into the water almost vertically via a tower on thevessel;andthe resulting profile ofthe pipeline between the bottom of the vesselandthe point whereit touches the ocean floor resembles a “J.” In case astinger is used, it is relatively short, becausetheload of the pipeline span is not asheavyand the requirementto control curvature in the overbend is reduced. This approachessentially overcomes limitations of the S-lay method in deep waters, where the weight ofthe suspended pipe increases, therebyexceeding the tensionerrequirements and practical design/fabrication limits. Additionally, the horizontal tension required for the J-lay method issmallercompared to that of the S-lay method because the span positioned in the J-lay methodcan withstand more motionandstronger underwater currents. Thepurpose here is simply to accommodate thesubmerged weight of the span, control stress,andto maintain satisfactory curvature in the sag-bend. Compared to the S-lay method, the J-laymethod is more accurate because the location ofthetouchdown point isnearthevessel. It alsoaffords fast and relatively safe abandonmentand recovery turnaroundas compared with the othertwo methods. On the other hand, the pipelayingrate is slowerthanin J-lay method and may be exacerbated by the extra time needed to weld together and non-destructively test (NDT) requirementsof the vertical sections of pipe. J-lay is not suitable for use in shallow waters. Ontheother hand, J-layis the preferredpipelaying method forusein deep water since reel-layandS-lay operations are not feasible in such situations. Still, in Deepwater scenarios, J-layrequires the pipelayingvesselsto be fitted with dynamic positioning systems toensure correct navigationandgeolocation. J-lay is also the preferredmethodwhen laying “PIP” pipelines,sincebending during layoperationis minimized. Figure 5-3 illustrates a J-lay vessel and pipelaying operations.

Fig. 5-3 J-layvessel withpipelaytower

Components of an Offshore Pipeline System An offshore pipeline system consists of various components in additionto the pipesthemselves(See Fig. 5-4). Some of the most common andimportant components are: Risers Pig launchers and receivers Mechanical support equipment (valves, pumps,compressors,etc.) Manifold systems Jumpers Umbilicals, instrumentation, andcontrol systems

Fig. 5-4 Componentsof an offshore pipeline system zEH-qreQzYM&imgdii=pMFvcxbHDyXTUM Risers Risers serveas the conduits through which hydrocarbons flowfromthesea floor to an offshore platform. They areessentially anintegral part of the platformstructure, representing the vertical part ofa pipeline system that extends from the baseof the platform to its top. They are commonlyincludedin the platform fabricationandoften arrive atthe construction site preinstalled as part of the platform jacket. Risers can be rigid orflexible.Rigid risers are generallypreinstalled, whereasflexible ones may or maynotbe. The flexible types are very adaptable,but they do have sizelimitations.

Catenaries are rigid risers oftenconstructedfromsteel that are usedin deep waterscenarios.They are verylong, curved orU-shapeddevices,thatare commonly associatedwith floating platforms. The main constraintis the negative impact of wave loads.

Once pipelayingoperationsare completed, the pipelineendnearest to theplatform is connectedto the bottom ofthe riser.Theriser generally endsat the faceof the pig launcher/receiver at adesignatedlocation on the floor ofthe platform. Sometimes, however, the riser can end at the insulating flange (a special partof the riser which separates it from the platform structure).

Risers are generally fabricated bya different vendor thanthe pipeline fabricator. Thereasonis that engineeringdesign and testingparametersfor risers aredifferent andmuch more stringent than those forthepipelinesystemitself,and coderequirements areusuallymuchtighter.

Pig Launchersand Receivers

While transporting oil and gas, pipelinescan become clogged over time. In anticipation of this situation,engineers make provisions forperiodiccleaningof thepipelines.This cleaning operation isverycostly since pipeline operationsmust generally cease beforehand.

Mechanical Support Equipment To ensure efficient operations, variousmechanicalequipment is required toregulate or controlflowand pressure, shut down pipeline operation, conducthydrotests, or perform other functions.Depending on whether the pipeline is transporting liquids or gases, pumps and/or compressors are required to keep thepressure on the product to maintain a specified velocity along thepipeline. Further, valves may beneeded to controlor shut down the flowas required. Different kinds of valves are used on oil andgaspipelines. Valve typeis alsodictated by functional variation (e.g.,pressurecontrol vs. metering) andoperational mechanism (e.g., manual vs. automatic). Automated valves function with actuators. Andactuatorsareof various typessuchas: electrically operated, spring loaded/mechanical, electro-hydraulic, and pneumatic. Manifold Systems Manifolds are subsea hub-like structures consisting of flow-routing equipment(valves, controlsystems,piping,jumpers,insulation,etc.) that providethe connections where pipelines end,meet,or change direction. For example,manifolds provide the connections between wellsandflowlines (see fig5-4).Manifolds are also usedto optimize the subsea pipelinelayoutand reduce the number of risers connectedto a platform. Amanifold can be part ofa simple one-pipelinesystemor a multi-pipeline system (seefig.5-4). If connectedto dual flowlines, amanifoldcan typically handle piggingandcan have the capabilityto route the flow of hydrocarbonsfrom a particularwellto a desired flowline via jumpers. Jumpers (see fig. 5-4) are pipeline segments used to connect manifold systems to wells.Jumpers can berigidor flexible lines ranging

from 4 to 18 in. indiameter andlengthsup to about 150 ft(50m). Tie-inconnections can be either verticalor horizontal,depending on systemselection.

Jumpers are generallydesigned to beusedin water depthsexceeding10,000ft (3,000 m) with pressuresup to 15,000 psi andcanaccommodatea number of features,including thermal insulation,vortex-inducedvibration strakes,flying leads(electrical, optical, and hydraulic),multi-phaseflowmeters, acousticdetection devices, seafloor metrology, and system integrationtesting (SIT) and support. Umbilicals, Instrumentation, andControl Systems An umbilical isa cable and/or hose, which carries multiple small cablesand pipescarryingrequiredconsumablesto subsea equipment (seefig.5-5).

Fig. 5-5. Umbilical cross section showingvariouscomponents For example,an umbilicalcan supply air fordiversandpower for pressure suits, as well ashydraulics,electricity,and fiber opticsto subsea equipment andsystems such as manifolds. Umbilicals alsodelivervarious chemicals and fluids toproductionsystems and support drillingoperations,wellmaintenance,and workoveractivities.Theyalso carry instrumentcontrol leads fordataacquisitionor remoteoperations (e.g., ROVs).

Quality Controlin Pipeline Fabrication Because pipelines transport fluids that canbe hazardousto humans and the environment, leakages ofanykind can be of great concern. Leaks can lead to seriousincidents,including blowouts,explosions, and fires involvingnot only the pipelines themselves, butthe platforms they service.The1988 Piper-Alfa disaster in the North Sea, whichdevelopedfroma gas pipelineblowout,is a clear example of the extent ofdamagethat can be done.In that case, several interconnected platformfacilities were destroyed, andscoresof workers were killed.