Embed Size (px)
Citation preview
woodplc.com
Assessing the Risk of Overpressure from
Liquid Thermal Expansion
Stephanie Cicchini, Jeff Zhang
Wood Process Solutions
• Introduction
– Liquid Thermal Expansion
– Background on Metocean (Meteorology & Oceanography)
• Modelling
– Methodology
– Benchmarking against Field Data
• Applications & Mitigation Measures
– Application 1: Subsea Tree Cavity
– Application 2: Offshore Hydrotesting Activities
– Application 3: Trapped Fluids during Operation
Outline
2 A presentation by Wood.
Introduction
3 A presentation by Wood.
Metocean – Location of Various Fields in WA
4 A presentation by Wood.
(Ref. Hengesh, J.V., Dirstein, J.K. and Stanley, A.J., “Landslide Geomorphology Along the Exmouth Plateau Continental Margin, North West Shelf, Australia”,. Published in the Australian Geomechanics Journal, Special Offshore Edition, December 2013, p.71-92.)
Seaw
ate
r D
ep
th (
m)
T (°C)
MinMeanMax
warmercolder
dee
per
Metocean – Diurnal Tides
5 A presentation by Wood.
Modelling
6
Contributing Factors to Liquid Thermal Expansion
7 A presentation by Wood.
Liquid
Thermal
Expansion
Seawater
temperature
variation
Fluid
properties
Pipe
properties
Required fluid properties:
Fluid Properties
8 A presentation by Wood.
Liquids Uses
MEG
• Commonly used as inhibitor to prevent/reduce hydrate formation
• Used for hydrotesting / leak testing
• Flooding medium after subsea installation
Water• Used for hydrotesting / leak testing
• Flooding medium after subsea installation
Required pipe properties:
Pipe Properties
9 A presentation by Wood.
Wall Material Uses
Steel
• Pipeline
• Main production system piping
• Umbilicals carrying inhibitors and chemicals for subsea injection
API 521 methodology used to give the pressure increase in a closed vessel due to
thermal expansion
Equation for Liquid Thermal Expansion
10 A presentation by Wood.
38
1318
2328
4.60E-04
4.80E-04
5.00E-04
5.20E-04
5.40E-04
5.60E-04
5.80E-04
20
96
17
2
24
8
32
5
40
1
47
7
55
3
T (°C)
αv
(1/°
C)
P (bara)38
1318
2328
3.30E-05
3.50E-05
3.70E-05
3.90E-05
4.10E-05
20
96
17
2
24
8
32
5
40
1
47
7
55
3
T (°C)
χ(1
/bar
)P (bara)
Equation for Liquid Thermal Expansion
11 A presentation by Wood.
Fluid Compressibility: Fluid Thermal Expansivity:
Model Schematic
12 A presentation by Wood.
Insulation/Burial (optional)
Closed NodeClosed Node
Pipe Wall Elasticity
Ambient = Seawater
Benchmarking (Field Data vs Cubic EoS vs High Accuracy EoS)
13 A presentation by Wood.
ΔP / ΔT (bar/°C)
Measured Field Data 9.7 – 11.1
Out of Box Standard Tools
(e.g. Cubic EoS)
~22 (CPA)
~21 (PR78)
~16 (RKSA)
High Accuracy EoS 10.6 (CSMA)
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36
Tem
pe
ratu
re
Time (h)
Benchmarking - Fluid Temperature
Measured Field Cubic EoS HighAccuracy EoS
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36P
ress
ure
Time (h)
Benchmarking - Pressure
Measured Field Cubic EoS High Accuracy EoS
Parameters
14 A presentation by Wood.
Sensitive
Change in Fluid Temperature (ΔT)
Fluid Thermal Expansivity (αV)
Fluid Compressibility (γ)
Insulation Thickness
Not Sensitive
Wall Elasticity (E)
Diameter to Wall Thickness Ratio
(D/t)
Wall Coefficient of Expansion (αl)
15
Applications and Mitigation Measures
Challenge:
– Large ΔT experienced from hot
production fluids heating up the
tree cavity
Application 1 – Subsea Tree Cavity
16 A presentation by Wood.
Approach:
CFD(complex
geometries)
Accurate
fluid
properties
Pressure
increase due
to thermal
expansion
Mitigation:
– In design: Account for liquid thermal expansion in design of subsea tree cavity.
Remove actuated valves where not required.
– In operation: Avoid trapped liquid situations such as dual isolation.
Requirement:
– Hydrotesting requires testing the system at high pressures for extended periods (e.g. 24 h at a holding pressure above design).
Challenge:
– Stabilizing pressure with varying seawater temperatures.
– Pressures above design, approaching burst limit.
Approach:
Mitigation:
– In design: Account for liquid thermal expansion in design of subsea systems (e.g. pipelines, structures, valves).
– In operation: Address through bespoke procedures.
Application 2 – Offshore Hydrotesting Activities
17 A presentation by Wood.
Seawater
temperature
variations
Accurate
fluid
properties
Pressure
increase due
to thermal
expansion
Challenge:
– Unplanned shutdown of pumps / valves
– Seawater temperature swings → pressure increases → possibly exceed design pressure
Application 3 – Trapped Liquids during Operation
18 A presentation by Wood.
Approach:
– As per Application 2.
Mitigation:
– In operation: Selecting an appropriate pump discharge PSV set point.
Pressure / temperature monitoring and high alarms.
(a) (b)T (°C)
MinMeanMax
warmercolder
• Liquid thermal expansion can lead to
increase in pressures possible above design.
• An approach was developed to assess
extent of liquid thermal expansion &
possible mitigations.
Key Take-Aways
19 A presentation by Wood.
Liquid
Thermal
Expansion
Seawater
temperature
variation
Fluid
properties
Pipe
properties
• Challenge in varying seawater temperature / nearby hot production fluids
resolved by:
– Appropriate modelling techniques & accurate input data
– Introducing mitigations
woodplc.com
For further information, please contact Stephanie Cicchini or Jeff Zhang
