1. Overview to Subsea
System
Sandeep S Rangapure
R 160206025
M.Tech ƛ Pipeline Engineering

2. Well head Platform
Riser
Process Platform
Pipeline crossing
Expansion Spool Piece
To shore
Grouted Supporting bag
Export lines
Well head
Existing line
Subsea mainfold
Tie in
Riser
Flowlines or Pipelines
Well head
Figure 1.1 Subsea System & Flowlines

3. Introduction
Subsea Pipelines are used for the transportation
of offshore Hydrocarbons from one Platform to
another and or Platform to Shore

4. DIFFERENT TYPES OF OFFSHORE PRODUCTION UNITS

5. 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;

6. SUBMARINE PIPELINE SYSTEMS
PIPELINE
Pipeline is defined as the part of a pipeline system which is
located below the water surface at maximum tide (except for
pipeline risers)
Pipeline may be resting wholly or intermittently on, or buried
below, the sea bottom
PIPELINE COMPONENTS
Any items which are integral part of pipeline system such as
flanges, tees, bends, reducers and valves
PIPELINE SYSTEM
An inter connected system of submarine pipelines, their risers,
supports, isolation valves, all integrated piping components,
associated piping system and the corrosion protection system

7. Risers
A Riser is a conducting pipe connecting sub-sea wellheads, templates or
pipelines to equipment located on a buoyant or fixed offshore structure.
Types of riser
Rigid riser
- for shallow water
Catenary steel riser - for deep water
Flexible riser
- for deep and shallow water
Riser clamp
Riser are supported/guided from the jacket members through
clamps
Types of Clamp
Hanger clamp
Fixed clamp
Adjustable clamp

9. Riser Clamp (Welding to Jacket member)

10. Restrained lines
Pipelines which cannot expand or contract in the longitudinal
direction due to fixed supports or friction between the pipe and soil
Unrestrained lines
Pipelines without substantial axial restraint. (Maximum one fixed
support and no substantial friction).
Platform
Platform
FL 1
FL 3
FL 4
Hanger clamp level
Sea surface level
Riser 1
FL 21
FL 20
FL 19
Riser 2
73.5 m
74 m
FL 5
0.00 m
2
m
FL 2
7.5 m 7.5 m
2
m 7.5 m 7.5 m
FL 22
1:7
1:7
FL 18
Sea bed
14 m 112 m
FL 6
FL 7
562.5 m
FL 8
500 m x 6 nos
FL 9 to 14
Concrete CTE coating
Monel coating
Paint
562.5 m
112 m 14 m
FL 15
FL 16
FL 17

11. 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

12. PIPELINE SIZING
In general it means fixing up the pipeline nominal
diameter (6Ɛ,10Ɛ etc.,) which deals with the important
aspects like...
MAXIMUM FLOW RATE CONDITION
CHECK FOR THE FLOW CONDITION (pressure drop
flow velocity)
CHECK FOR SECONDARY CRITERIA like Ʀ.
# Flow regime (mix of hydro carbon, single/multi phase
flow)
# Temperature profile
# Erosion velocity

13. D
t

14. PIPELINE MATERIAL SELECTION
The governing parameters for the particular type of material to
be used are
Temperature
Pressure
Surrounding Environment.
Environment.
Corrosive elements (CO2 and H2 S)
Carbon steel (Carbon - Manganese Steel) C.S.Nace, C.R.A.
Steel)
p
API - 5L of Grade Ranges From X - 42 to X - 80
p
X-80 - Toughness and Weldability are limitations
p
API - 5L X- 52 ,60 65 Grades are commonly used.
used.

15. PIPELINE MECHANICAL DESIGN
The mechanical design of the pipeline is carried to with stand factors like
Internal pressure
External Pressure
Do
Hydrostatic Collapse
Di
Buckle initiation
Buckle Propagation
Po
Po
Po
Pi
W
W
ho
ho

17. PIPELINE SPAN ANALYSIS
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
Longitudinal loads
Unsupported length

19. PIPELINE STABILITY
Pipeline once installed at the sea bed should be sufficiently stable
to avoid any overstressing, deterioration of coating etc., due to
wave and current generated movements
PIPELINE STABILITY
Vertical stability
Lateral stability

20. Vertical stability
Sinking in to the sea bed during maximum fluid density
condition.
Floating of Buried Pipeline during Empty condition Soil
Liquefaction.
The Pipe sinkage is determined as the depth at which the applied
pipe pressure equals the soil bearing resistance.
Soil deformation(pipe sinkage)H,is given by:
sinkage)H
H = D/2-[(D/2)2 ± (B/2)2]1/2
D/2-
Where,
D = Overall pipe outside diameter including pipe coatings
B = Projected contact area between pipe and soil =P/qu
Where,
qu = CNC +1/2BK NK
+1/2BK
qu = Ultimate bearing capacity of soil
P = Pipe submerged weight including pipe coatings and in water
filled condition per unit length.

21. Lateral stability
It is the capacity to resist the lateral forces due to
Environmental loads.
Forces to be considered for Lateral stability analysis
Submerged weight WS
Lateral resistance R
Friction Q
Drag force FD
Lift force FL

22. The stability criterion is expressed as
(Ws - FL) Q u (FD + FI) S
Where,
S
Ws
FL
FD
FI
Q
=
=
=
=
=
=
safety factor (1.1)
submerged weight of pipeline/unit
length, for nominal wall thickness
(t), N/m
hydrodynamic lift force, N/m
hydrodynamic drag force, N/m
hydrodynamic inertia force, N/m
lateral coefficient of friction between
pipe and seabed.

23. Methods of Pipeline stabilization
Increase Pipeline wall thickness
Provide Concrete Weight Coating
Lay the Pipeline in Open trench
Trench and bury the Pipeline
Provide Concrete Mattress over Pipeline
Stabilize Pipeline by Rock dumping

24. Increase in
Pipewall thickness
Providing
Concrete coating

25. Sea bed
Tren h
all
Natural fill
Buried pipe- Natural Fill
Jetted in pipe
Tremie concrete
rmor rock
Back fill
Bedding
Buried pipe- Armor Cover
Bedding
Buried pipe- Concrete Cover
Stabilization Methods for buried Submarine pipeline

26. Trenching
Concrete Mattress

27. Rock dumping

28. PIPELINE CROSSING ANALYSIS
Crossings are designed to Give a Physical separation
Between The Proposed Line Existing Line.
To Avoid Interfacing Of Cathodic Protection Between
The Two Lines
A min of 300mm gap is Provided b/w the lines as per the DNVDNVCode.

29. Crossing analysis methodology
»
Pipeline Crossing Span Calculation.
Pipeline Dynamic Span Calculation
»
Number of Supports to be Provided.
»
Pipeline Crossing Flexibility analysis
»
Pipeline Crossing Support design against,
»
Bearing capacity
Over turning
Sliding
Settlement

30. PIPELINE CATHODIC PROTECTION SYSTEM DESIGN
The Subsea pipelines are provided with sacrificial anodes made of
Aluminum or Zinc to protect against marine corrosion
Important parameters for Anode Design
*
Surface area of the Pipeline
*
Fluid and Anode temperature
*
Break down
*
Design service life of Anodes

33. MAJOR DESIGN CODES AND STANDARDS
DNV 1981
DNV 2000
- Rules for submarine pipeline system
- Submarine pipeline system
API 5L
- Specification for line pipe
BS 8010
- Code of practice for pipeline
NACE RP 0169 - Recommended practice,control of external
corrosion on underground or submerged
metallic piping.
OISD 141
- Design and construction requirements for
cross country hydrocarbon pipeline.
ASME B 31.8
system.
-Gas transmission and distribution piping
ASME B 31.4
- Pipeline transportation systems for liquid
hydrocarbon and other liquids