Overview to Overview to Subsea SystemSubsea System

Sandeep S RangapureSandeep S Rangapure

R 160206025R 160206025

M.Tech – Pipeline M.Tech – Pipeline EngineeringEngineering

Well head

Subsea mainfold

Well head

Flowlines or Pipelines

Export lines

Process Platform

Well head Platform

Expansion Spool Piece

Tie in

Pipeline crossing

Grouted Supporting bag

Riser

Riser

To shore

Existing line

Figure 1.1 Subsea System & FlowlinesWell head

Subsea mainfold

Well head

Flowlines or Pipelines

Export lines

Process Platform

Well head Platform

Expansion Spool Piece

Tie in

Pipeline crossing

Grouted Supporting bag

Riser

Riser

To shore

Existing line

Figure 1.1 Subsea System & Flowlines

IntroductionIntroduction

Subsea Pipelines are used for the transportation of offshore Hydrocarbons

from one Platform to another and or Platform to Shore

DIFFERENT TYPES OF OFFSHORE PRODUCTION UNITSDIFFERENT TYPES OF OFFSHORE PRODUCTION UNITS

Pipelines are used for a number of purposes in the development of offshore hydrocarbon resources These include e.g.:

Export (transportation) pipelines

Pipeline bundles.

Flowlines to transfer product from a platform to export lines

Water injection or chemical injection Flowlines

Flowlines to transfer product between platforms

Subsea manifolds and satellite wells;

SUBMARINE PIPELINE SYSTEMS SUBMARINE PIPELINE SYSTEMS

PIPELINEPIPELINE Pipeline is defined as the part of a pipeline system which is Pipeline is defined as the part of a pipeline system which is

located below the water surface at maximum tide (except for located below the water surface at maximum tide (except for pipeline risers)pipeline risers)

Pipeline may be resting wholly or intermittently on, or buried Pipeline may be resting wholly or intermittently on, or buried below, the sea bottombelow, the sea bottom

PIPELINE COMPONENTSPIPELINE COMPONENTS Any items which are integral part of pipeline system such as Any items which are integral part of pipeline system such as

flanges, tees, bends, reducers and valvesflanges, tees, bends, reducers and valves

PIPELINE SYSTEMPIPELINE SYSTEM An inter connected system of submarine pipelines, their An inter connected system of submarine pipelines, their

risers, supports, isolation valves, all integrated piping risers, supports, isolation valves, all integrated piping components, associated piping system and the corrosion components, associated piping system and the corrosion protection systemprotection system

RisersA Riser is a conducting pipe connecting sub-sea wellheads, templates orpipelines to equipment located on a buoyant or fixed offshore structure.

Types of riser

Rigid riser - for shallow waterCatenary steel riser - for deep waterFlexible riser - for deep and shallow water

Riser clampRiser are supported/guided from the jacket members through clamps

Types of Clamp

Hanger clampFixed clampAdjustable clamp

Riser Clamp (Welding to Jacket member)

Restrained linesPipelines which cannot expand or contract in the longitudinal

direction due to fixed supports or friction between the pipe and soil

Unrestrained linesPipelines without substantial axial restraint. (Maximum one fixed

support and no substantial friction).

7.5

m2 m

74

m

Sea bed

0.00 m7.5

m

7.5

m2 m

73

.5 m

7.5

m

Riser 1 Riser 2

112 m14 m 14 m112 m562.5 m562.5 m 500 m x 6 nos

Hanger clamp level

Sea surface level

Platform Platform

Concrete & CTE coating

Monel coating

Paint

FL 1

1:7

1:7

FL 2

FL 3

FL 5

FL 6 FL 7 FL 8 FL 9 to 14 FL 15 FL 16 FL 17

FL 18

FL 20

FL 21

FL 22

FL 4 FL 19

7.5

m2 m

74

m

Sea bed

0.00 m7.5

m

7.5

m2 m

73

.5 m

7.5

m

Riser 1 Riser 2

112 m14 m 14 m112 m562.5 m562.5 m 500 m x 6 nos

Hanger clamp level

Sea surface level

Platform Platform

Concrete & CTE coating

Monel coating

Paint

Concrete & CTE coating

Monel coating

Paint

FL 1

1:71:7

1:71:7

FL 2

FL 3

FL 5

FL 6 FL 7 FL 8 FL 9 to 14 FL 15 FL 16 FL 17

FL 18

FL 20

FL 21

FL 22

FL 4 FL 19

SUBSEA PIPELINE DESIGN ACTIVITIES

Pipeline Sizing

Pipeline Material Selection

Pipeline Mechanical Design

Pipeline Stability Analysis

Pipeline Span Analysis

Pipeline Crossing Design

Pipeline Cathodic Protection System Design

PIPELINE SIZINGPIPELINE SIZING

In general it means fixing up the pipeline nominal diameter In general it means fixing up the pipeline nominal diameter (6”,10” etc.,) which deals with the important aspects like...(6”,10” etc.,) which deals with the important aspects like...

MAXIMUM FLOW RATE CONDITIONMAXIMUM FLOW RATE CONDITION

CHECK FOR THE FLOW CONDITION (pressure drop & flow CHECK FOR THE FLOW CONDITION (pressure drop & flow velocity) velocity)

CHECK FOR SECONDARY CRITERIACHECK FOR SECONDARY CRITERIA like …. like ….

# Flow regime (mix of hydro carbon, single/multi phase # Flow regime (mix of hydro carbon, single/multi phase

flow) flow) # Temperature profile # Temperature profile

# Erosion velocity# Erosion velocity

DDtt

PIPELINE MATERIAL SELECTIONPIPELINE MATERIAL SELECTION

The governing parameters for the particular type of The governing parameters for the particular type of material to be used are material to be used are

TemperatureTemperature

PressurePressure

Surrounding Environment.Surrounding Environment.

Corrosive elements (COCorrosive elements (CO22 and H and H22 S) S)

Carbon steel (Carbon steel (Carbon - Manganese SteelCarbon - Manganese Steel) C.S.Nace, C.R.A) C.S.Nace, C.R.A.. API - 5L of Grade Ranges From X - 42 to X - 80API - 5L of Grade Ranges From X - 42 to X - 80 > X-80 - Toughness and Weldability are limitations> X-80 - Toughness and Weldability are limitations API - 5L X- 52 ,60 & 65 Grades are commonly used.API - 5L X- 52 ,60 & 65 Grades are commonly used.

PIPELINE MECHANICAL DESIGNPIPELINE MECHANICAL DESIGN

The mechanical design of the pipeline is carried to with stand The mechanical design of the pipeline is carried to with stand factors like factors like

Internal pressureInternal pressure

External PressureExternal Pressure

Hydrostatic CollapseHydrostatic Collapse

Buckle initiationBuckle initiation

Buckle PropagationBuckle Propagation

Po

Do

Di

ho

ho

Pi

Po

Po

Po

Do

Di

ho

ho

Pi

Po

Po

Po

Do

Di

ho

ho

Pi

Po

Po

Po

Do

Di

ho

ho

Pi

Po

Po

PIPELINE SPAN ANALYSIS

Unsupported length

Longitudinal loadsLongitudinal loads

Causes of the Pipeline Spans are Uneven Seabed on Selected route Pipeline Crossing seabed rock outcrop Sand Waves Scour All these result in spanning and cause

Excessive yielding (Results in High Bending Moments) Buckle Initiation and there by Propagation

PIPELINE STABILITYPIPELINE STABILITY

Pipeline once installed at the sea bed should be sufficiently Pipeline once installed at the sea bed should be sufficiently stable to avoid any overstressing, deterioration of stable to avoid any overstressing, deterioration of coating etc., due to wave and current generated coating etc., due to wave and current generated

movementsmovements

PIPELINEPIPELINE STABILITYSTABILITY

Vertical stabilityVertical stability Lateral stabilityLateral stability

Vertical stabilityVertical stability Sinking in to the sea bed during maximum fluid density condition.Sinking in to the sea bed during maximum fluid density condition. Floating of Buried Pipeline during Empty condition & Soil Liquefaction.Floating of Buried Pipeline during Empty condition & Soil Liquefaction. The Pipe sinkage is determined as the depth at which the applied pipe The Pipe sinkage is determined as the depth at which the applied pipe

pressure equals the soil bearing resistance.pressure equals the soil bearing resistance. Soil deformation(pipe sinkage)Soil deformation(pipe sinkage),is given by:,is given by:

= D/2-[(D/2)= D/2-[(D/2)22 – (B/2) – (B/2)22]]1/21/2

Where,Where, D = Overall pipe outside diameter including pipe coatingsD = Overall pipe outside diameter including pipe coatings B = Projected contact area between pipe and soil =P/quB = Projected contact area between pipe and soil =P/quWhere,Where, qu = CNqu = CNC C +1/2B+1/2B N N qu = Ultimate bearing capacity of soilqu = Ultimate bearing capacity of soil P = Pipe submerged weight including pipe coatings and in water filled P = Pipe submerged weight including pipe coatings and in water filled

condition per unit length.condition per unit length.

Lateral stabilityLateral stability It is the capacity to resist the lateral forces due to It is the capacity to resist the lateral forces due to

Environmental loads.Environmental loads. Forces to be considered for Lateral stability analysisForces to be considered for Lateral stability analysis

Submerged weight WSubmerged weight WSS

Lateral resistance RLateral resistance R

Friction Friction

Drag force FDrag force FDD

Lift force FLift force FLL

The stability criterion is expressed as The stability criterion is expressed as (Ws - F(Ws - FLL) ) (F (FDD + F + FII) S) S Where,Where,

SS == safety factor (1.1)safety factor (1.1)W sW s == submerged weight of pipeline/unit submerged weight of pipeline/unit

length, for nominal wall thickness length, for nominal wall thickness (t), N/m(t), N/m FFLL == hydrodynamic lift force, N/mhydrodynamic lift force, N/m FFDD == hydrodynamic drag force, N/mhydrodynamic drag force, N/m FFII == hydrodynamic inertia force, N/mhydrodynamic inertia force, N/m == lateral coefficient of friction between lateral coefficient of friction between

pipe and seabed.pipe and seabed.

Increase Pipeline wall thicknessIncrease Pipeline wall thickness Provide Concrete Weight CoatingProvide Concrete Weight Coating Lay the Pipeline in Open trenchLay the Pipeline in Open trench Trench and bury the PipelineTrench and bury the Pipeline Provide Concrete Mattress over Pipeline Provide Concrete Mattress over Pipeline Stabilize Pipeline by Rock dumpingStabilize Pipeline by Rock dumping

Methods of Pipeline stabilizationMethods of Pipeline stabilization

Increase in Pipewall thickness

Increase in Pipewall thickness

Providing Concrete coating

Providing Concrete coating

Sea bed

Trench wall

Jetted in pipeBuried pipe- Natural Fill

Armor rock

Back fill

Bedding Bedding

Tremie concrete

Buried pipe- Armor Cover Buried pipe- Concrete Cover

Stabilization Methods for buried Submarine pipeline

Natural fill

Trenching Concrete Mattress

Rock dumping

PIPELINE CROSSING ANALYSISPIPELINE CROSSING ANALYSIS

Crossings are designed to Give a Physical Crossings are designed to Give a Physical separation Between The Proposed Line & separation Between The Proposed Line & Existing Line.Existing Line.

To Avoid Interfacing Of Cathodic Protection To Avoid Interfacing Of Cathodic Protection Between The Two LinesBetween The Two Lines

A min of 300mm gap is Provided b/w the lines as per the A min of 300mm gap is Provided b/w the lines as per the DNV-Code.DNV-Code.

Crossing analysis methodologyCrossing analysis methodology

» Pipeline Crossing Span Calculation.Pipeline Crossing Span Calculation.» Pipeline Dynamic Span CalculationPipeline Dynamic Span Calculation» Number of Supports to be Provided.Number of Supports to be Provided.» Pipeline Crossing Flexibility analysisPipeline Crossing Flexibility analysis» Pipeline Crossing Support design against, Pipeline Crossing Support design against,

> Bearing capacityBearing capacity> Over turningOver turning> SlidingSliding> SettlementSettlement

PIPELINE CATHODIC PROTECTION SYSTEM DESIGN

The Subsea pipelines are provided with sacrificial anodes made of Aluminum or Zinc to protect against marine corrosion

* Surface area of the Pipeline

* Fluid and Anode temperature

* Break down

* Design service life of Anodes

* Surface area of the Pipeline

* Fluid and Anode temperature

* Break down

* Design service life of Anodes

Important parameters for Anode Design

MAJOR DESIGN CODES AND MAJOR DESIGN CODES AND STANDARDSSTANDARDS

DNV 1981 - Rules for submarine pipeline systemDNV 1981 - Rules for submarine pipeline system DNV 2000DNV 2000 - Submarine pipeline system - Submarine pipeline system API 5L - Specification for line pipeAPI 5L - Specification for line pipe BS 8010 - Code of practice for pipelineBS 8010 - Code of practice for pipeline NACE RP 0169 - Recommended practice,control of external NACE RP 0169 - Recommended practice,control of external

corrosion on underground or submerged corrosion on underground or submerged metallic piping. metallic piping.

OISD 141 - Design and construction requirements for OISD 141 - Design and construction requirements for cross country hydrocarbon pipeline. cross country hydrocarbon pipeline.

ASME B 31.8 -Gas transmission and distribution piping system.ASME B 31.8 -Gas transmission and distribution piping system. ASME B 31.4 - Pipeline transportation systems for liquid ASME B 31.4 - Pipeline transportation systems for liquid

hydrocarbon and other liquids hydrocarbon and other liquids