1 © 2013 ANSYS, Inc. September 19, 2014 ANSYS Confidential
Erosion Analysis of Subsea Equipment: A Case Study With High Solid Loading
2014 Convergence Conference
Uday Godse, Prospect Flow
energy engineering
Erosion analysis of Subsea equipment
A case study with high solid loading
Presented by: Uday Godse, PhD, P.E
QMF 21 Rev 3
Content
• Prospect introduction
• Fundamentals of erosion analysis
• Erosion models used in CFD
• Low sand loading – Examples
• Moving deforming mesh (MDM) by Ansys-Fluent
• A case study with high solid loading
– Approach
– Results
• Summary
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 2
QMF 21 Rev 3
Prospect introduction
• Leaders in engineering, design and analysis providing solutions to
the upstream oil and gas industry and wider energy sector since
1999
• Prospect global locations
– Houston
– Aberdeen
– Derby
– Stavanger^
– Dubai^
^ WWC 22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 3
QMF 21 Rev 3
Prospect’s value
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 4
EN
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Engin
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Experience
QMF 21 Rev 3
ANSYS history & usage
• An ANSYS customer since 1999
• Fluent – Gas Dispersion
– Multi-phase flow
– Thermal analysis
– Erosion prediction
• Mechanical
• Work bench
• AQWA
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 5
QMF 21 Rev 3
Flow analysis capabilities
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 6
• Prospect routinely analyses thermal behaviour of subsea
components, gas dispersion, multiphase separators, containment
systems used during emergency response
• Prospect has over 10 years experience in predicting flow induced
erosion and has used advanced methods such as computational
fluid dynamics extensively throughout that period
• Prospect has successfully completed over 70 erosion prediction
jobs for a range of clients placing at the forefront of erosion
prediction in the oil and gas industry
Fundamentals of erosion analysis
QMF 21 Rev 3
Background
• Accurate erosion predictions are very critical to risk
management studies
• Erosion of wall material is mainly due to the cutting action or
repeated plastic deformation caused by the particles impacting
the wall
• Erosion damage depends on impact parameters and mechanical
properties of the material
• The impact parameters include impact angle, impact velocity and
size, shape and density of the particles under consideration
• The mechanical properties include density and material hardness
of the material
• Erosion predictions range from simple to very complex
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 8
QMF 21 Rev 3
Approaches
• API 14E
• DNV RP O501
or Tulsa E/CRC
• CFD
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 9
𝑣𝑒=
𝑐
𝜌𝑚
Incr
eas
ing
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ple
xity
QMF 21 Rev 3
Erosion models
• Prospect has experience with the primary erosion models used
in the oil and gas industry:
– Tulsa Model
– DNV
– Oka
• All of these models have a similar form
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 10
)()( 59.0 fVFBHCe n
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QMF 21 Rev 3
Erosion vs. Angle of impact
• Most industry accepted models for erosion include an angle
function to reflect the influence of impact angle, f(alpha)
• A typical example is shown
• As can be seen, angle function is very sensitive to the type of
material
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 11
0
0.2
0.4
0.6
0.8
1
1.2
0 10 20 30 40 50 60 70 80 90 100
Brittle
Ductile
Angle
QMF 21 Rev 3
Typical erosion problems
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 12
• CFD can tackle any flow geometry but is most typically used to
examine the following types of equipment:
– Trees and flow lines
– Chokes
– General pipe networks
• CFD can tackle any flow conditions such as:
– Production flow – light sand loading
– Frac flows & well kills – heavy sand/particle loading
– Blow out conditions – extreme flow conditions
• CFD can address erosion wear and its effect on erosion rate
QMF 21 Rev 3
General flow networks
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Normalized
Erosion Rate 1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
CONTOURS OF EROSION RATE
QMF 21 Rev 3
Erosion in Plug tee
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2.74 mm/yr
1.71 mm/yr
CONTOURS OF EROSION RATE ON PLUG TEE
FLOW
[mm/yr]
QMF 21 Rev 3
Erosion of pristine geometry
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 15
IMAGE SHOWING THE CONTOUR OF EROSION RATE [mm/hr]
PEAK EROSION
RATE 14.43 MM/HR
SECONDARY EROSION
RATE ~ 3.5 MM/HR
QMF 21 Rev 3
Erosion of worn geometry
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IMAGE SHOWING THE CONTOUR OF EROSION RATE [mm/hr]
PEAK EROSION
RATE 5.33 MM/HR
SECONDARY EROSION
RATE ~ 2 MM/HR
QMF 21 Rev 3
Pristine vs. Eroded geometry
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Initial particle trajectory
Particle trajectory for eroded wall
Low sand loading – Production scenario
QMF 21 Rev 3
Low sand - 5D bend test
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0
0.0000005
0.000001
0.0000015
0.000002
0.0000025
0.000003
0.0000035
0 10 20 30 40 50 60 70 80 90
Ero
sio
n R
ate
(m
/kg s
an
d)
Ang le round bend (Degrees)
CFD
DNV Test
Flow conditions:
Inlet mixture velocity: 36.3 m/s
Mixture density: 72.3 kg/m3
Mixture viscosity: 1.8E-5 kg/m-s
Pipe ID: 26.5 mm
Particle size: 250 micron
Sand volume fraction < 1%
Low sand loading – Fracking scenario
QMF 21 Rev 3
Fracking – Inlet manifold
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INLET MANIFOLD SHOWING ORIGINAL CAD (LEFT) AND SIMPLIFIED GEOMETRY (RIGHT)
SLURRY INLET
WATER INLET
OUTLET
REGION OF POTENTIAL
EROSION
WATER INLET
WATER INLET
Flow conditions:
Fluid flow rate: 16 m3/min
Fluid density: 1017 kg/m3
Fluid viscosity: 4 cP
Sand rate: 26 kg/s
Particle size: 300 micron
Sand volume fraction: 4%
QMF 21 Rev 3
Fracking – Steady-state
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mm/min
Manifold after 24 days
Maximum eroded depth: 18 mm
CFD predictions
Extrapolated depth: 1140 mm
CFD predictions >> Measurements
IMAGE SHOWING THE CONTOUR OF EROSION RATE [MM/MIN]
QMF 21 Rev 3
Erosion - Moving deforming mesh
• The erosion rates predicted using a steady-state system can be
very conservative and may or may not represent reality
• For more accurate predictions of erosion rate there is a need to
account for the change in wall position
• Erosion-MDM coupling module is available in Ansys-Fluent
• The erosion module dynamically changes the surface wall
position based on the erosion at regular time intervals
• The wall face nodes are moved by a distance based on the
erosion rates
• The erosion study was re-visited using the erosion-MDM module
and the results are presented next
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QMF 21 Rev 3
Fracking scenario – Erosion MDM
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After 6 hrs
~2 mm
After 12 hrs
~4 mm
After 18 hrs
~5.6 mm
After 24 hrs
~6.8 mm
m
IMAGE SHOWING THE CONTOUR OF CUMULATIVE ERODED WALL DISTANCE [M]
QMF 21 Rev 3
0
2
4
6
8
10
12
14
16
0 4 8 12 16 20 24 28 32 36 40 44
Peak
ero
sion [
mm
]
Frac time [Hrs]
CFD-Steady State CFD-MDM
Fracking scenario – Extrapolated CFD data
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CFD (steady state) >> Measurements
CFD (MDM) ~ Measurements
1140 mm vs. 32 mm
Extrapolation
Extrapolation
QMF 21 Rev 3
Fracking scenario – Summary
• Steady-state analysis using linear extrapolation can yield order of
magnitude conservative erosion rates
– 1140 mm vs. 18 mm Measured value
• Erosion-MDM module in Ansys-Fluent is a viable option for
better erosion estimates
– 32 mm vs. 18 mm Measured value
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High sand loading – Well kill scenario
QMF 21 Rev 3
Well kill scenario – Simple elbow test
• A case study with high solid loading (~40% solid by volume)
representing a well kill scenario is presented next
• A simple elbow has been considered for this study
• Prospect has been involved in multiple validation studies at the
moment to validate the CFD analysis against the test data with
high solid loading
• The modeling approach is presented next
• The approach is followed by some normalized results after few
hours of operation
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QMF 21 Rev 3
Approach
• Eulerian granular multiphase model was utilized to account for
the particle-particle and the particle-fluid phase interactions
• Moving deforming mesh module was utilized
• Due to high solid loading the particles travel nearly parallel to the
wall surface and hence erosion due wall shear stress is more
dominant than erosion due to particle impact
er_shear = A (Vp)n SS
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• In order to account for both erosion mechanisms (wall shear and
impact based erosion), the combined effects of both the models
were considered:
er_total = er_impact + er_shear
QMF 21 Rev 3
Well kill scenario – Eroded distance
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ORIGINAL GEOMETRY
Normalized
Eroded distance
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
DEFORMED GEOMETRY
Flow conditions:
Inlet velocity: 25 m/s
Fluid density: 1800 kg/m3
Fluid viscosity: 50 cP
Particle size: 100 micron
Solid volume fraction: 40%
QMF 21 Rev 3
Well kill scenario – Erosion rates
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IMPACT BASED RATES
Normalized
Erosion rates
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
SHEAR BASED RATES
Hot spot on turn will
reduce as flow continues
to erode the turning edge
Shear will continue
contributing and will become
the primary erosion
mechanism as flow continues
QMF 21 Rev 3
Well kill scenario – Summary
• Well kill scenario is a work in progress
• High-solid loading needs special treatment on account of the
erosion induced due wall shear stress
• Abrasive (shear stress) erosion model in Ansys-Fluent can
account for the wall shear stress induced due to the particles
travelling nearly parallel to the wall surface
• Additional model means more modeling parameters to tune
• Erosion-MDM can be coupled and more realistic results can be
obtained
22 May 2014 Erosion analysis of subsea equipment - A case study with high solid loading 32