Thermal expansion of offshore pipelines was analyzed. The document discussed how temperature changes cause pipelines to expand based on coefficients of linear expansion. It described how pipeline expansion is countered by friction with the seabed, potentially causing stresses. The analysis method of Palmer and Ling was used to model temperature profiles and calculate end expansion. Input data on the pipeline properties and environment were provided. Solutions like expansion spools were presented to absorb excessive expansion and protect risers.

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THERMAL EXPANSION ANALYSIS FORTHERMAL EXPANSION ANALYSIS FOR
OFFSHORE PIPELINEOFFSHORE PIPELINE
BY
NWAIWU, ZEPH
PIPELINE DISCIPLINE

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Introduction
Thermal expansion is the dimensionalThermal expansion is the dimensional
incremental changes exhibited by solids,incremental changes exhibited by solids,
liquids and gases in response to temperatureliquids and gases in response to temperature
changeschanges

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Primarily, expansion can be calculated thus:Primarily, expansion can be calculated thus:
∆∆L=L= αα LL ∆∆TT
WhereWhere
∆∆LL = Expansion (m, inch)= Expansion (m, inch)
∆∆TT = Change in temperature (= Change in temperature (°°C,C, °°F)F)
αα = Coefficient of Linear Expansion (m/m= Coefficient of Linear Expansion (m/m
°K, inch/inch °°K, inch/inch °F)F)
LL = initial length of pipeline (m, inch)= initial length of pipeline (m, inch)

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Background: Pipeline Expansion
Longitudinal expansion in pipeline is
caused by temperature and pressure
differential between the ambient conditions
of the surrounding seawater and prevailing
condition of the pipeline during Hydrotest
and operational phases
Consider a straight submarine pipelineConsider a straight submarine pipeline
connected to a platform riser.connected to a platform riser.

5. Thermal Expansion Analysis for Offshore Pipeline
The riser passes through clamps on theThe riser passes through clamps on the
platform, and then has a 90° bend. At aplatform, and then has a 90° bend. At a
short distance from the platform, theshort distance from the platform, the
pipeline reaches the bottom, and from therepipeline reaches the bottom, and from there
on is continuously in contact with the soil.on is continuously in contact with the soil.
Because the temperature and pressure areBecause the temperature and pressure are
higher, the pipeline tend to expand. Thehigher, the pipeline tend to expand. The
frictional resistance between the pipelinefrictional resistance between the pipeline
and seabed is always counteracting theand seabed is always counteracting the
pipeline expansion.pipeline expansion.

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Explanation to Pipeline Expansion
Depending on the length of the pipeline, atDepending on the length of the pipeline, at
some distance from the platform, a pointsome distance from the platform, a point
termed anchor point may occur at which thetermed anchor point may occur at which the
forces producing expansion are counteractedforces producing expansion are counteracted
by the cumulative effects of the soil frictionalby the cumulative effects of the soil frictional
force.force.
Thus longitudinal expansion stresses are setThus longitudinal expansion stresses are set
up.up.

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Explanation to Pipeline Expansion
At the platform, however, the pipeline is onlyAt the platform, however, the pipeline is only
slightly constrained (by the vertical legs of theslightly constrained (by the vertical legs of the
riser, which is relatively flexible) and there itriser, which is relatively flexible) and there it
can expand freely and move towards thecan expand freely and move towards the
platform)platform)
At the platform, these movements areAt the platform, these movements are
important because they can overstress the riserimportant because they can overstress the riser
and the elbow.and the elbow. It is important to quantifyIt is important to quantify
pipeline expansion in order to access its effectpipeline expansion in order to access its effect
on the riser during riser stress analysis.on the riser during riser stress analysis.

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Industry Codes and standards and MPN Global Practices
The following MPN Global Practices and International Codes
and Standards are used in Pipeline Expansion calculations:
COMPANY/MPN Global Practices:
GP 86-01-01- Offshore Pipeline Design.
GP 86-01-01S- Offshore Pipeline Design – MPN Supplement
International Codes and Standards:
ASME B31.8- Gas Transmission and Distribution Piping Systems.
BS 8010-3 – Pipelines on subsea: Design, construction and
Installation
DNV-OS-F101 - Submarine Pipeline Systems.

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Method of Analysis
The analytical formulation given by Palmer
and Ling (1981) is been used to estimate
pipeline end expansion.
The temperature and pressure are simulated
along the pipeline using continuity and
momentum equation, and the simulated
inlet and outlet temperatures and pressures
are used for the expansion analysis.
The temperature profile is also evaluated
using the logarithm decay formula proposed
by palmer and Ling

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The Palmer and Ling basic formulation is
given as:
θ(x) = θ1 exp(-x/λ)
Where:
θ(x) is the temperature difference between
the pipeline and the water at a distance x
from the platform.
θ1 = Temperature difference at the platform
λ = Decay length

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Calculations
Pipeline is assumed straight and lying unburied
on the seabed.
The following input data are used;
• Pipeline properties
• Corrosion and Concrete Coating properties
• Minimum contents weights
• Temperature Profile and Pressure Profile
• Geotechnical Data

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Typical Design Data – Line Pipe
Parameters Units Ekpe-Asabo Pipeline
Pipeline outside diameter inch 16.00
Wall thickness inch 0.438
Approximate length ft (m) 63,234.5 (19,273.9)
Adopted length (including
riser sections)
64,466.2 (19659.4)
Concrete coating thickness inch 1.5
Minimum water depth ft (m) 140 (42.7)
Maximum water depth ft(m) 161 (49.1)

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Parameters Notation Value Units
Material density 490 lb/ft3
Young modulus E 30 X 103
psi
Poisson ratio ν 0.3
Specified minimum yield strength SMYS 65000 psi
Steel thermal conductivity 1.16 X 10-5
°F
Design temperature 150 °F
Operating temperature 105 °F
Hydrotest temperature 75 °F
Corrosion coating thickness tcc 0.027 In
Concrete coating thickness tcon 1.5 in
Density of liquid ρf 53.745 lb/ft3
Density of steel ρs 490 lb/ft3
Density of water ρw 64 lb/ft3
Density of corrosion coating ρcc 90 lb/ft3
Density of concrete coating ρcon 190 lb/ft3
Typical Design Data Continued

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SOLUTION TO THERMAL EXPANSION
If the pipeline expansion is of limited
magnitude, an effective and cost effective
design is obtained by letting the expansion
be taken by elastic deformation of the riser.
Where pipeline expansion is excessive
expansion loop will be required to absorb
some of the expansion, thereby protecting
the riser, its supports and associate jacket
members from overstressing.

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EXPANSION SPOOL DRAWING
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EXPANSION SPOOL
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EXAMPLE OF PLATFORM APPROACH

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Any
Questions

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