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OPTIMIZATION OF OFFSHORECATHODIC PROTECTION SYSTEMS
ICORR LONDON 8 APRIL 2021
MATTHEW L. TAYLOR, PH.D.
WHY OPTIMIZE?INTRODUCTION
Advantages
• Improving performance
• Reducing costs
• Reducing risk
• Declaring “optimal” without validation or qualifications. A better solution is not the “best” solution.
• Guess and Check.
Common Pit-Falls
Icorr London | April 8th 2021 | Matthew L. Taylor
TERMINOLOGYOPTIMIZATION
• Function: The model we evaluate
• Solution : List of proposed input values
• Results : Outputs from a model for a
given set of inputs.
Icorr London | April 8th 2021 | Matthew L. Taylor
TERMINOLOGYOPTIMIZATION
• Fitness function: Quantified “goodness”
• Constraints: Limit allowed solutions
• Optimal solution: The best solution (so far)
• Globally optimal: No other “better” solutions exist.
• Search space: for a “n” variable model, the search space is a n-dimensional hyper-
volume bounded by the maximum and minimum values for each variable.
Icorr London | April 8th 2021 | Matthew L. Taylor
OPTIMIZATIONSACP DESIGN
A Solution
Model Outputs
(CP Design)
Design
Equations
Constants
OBJECTIVE
Constraint(s)FITNESS
How much
Wasted mass?
“Better”
FITNESS
How many
Installs?
“Better”
Icorr London | April 8th 2021 | Matthew L. Taylor
TERMINOLOGYMULTIPLE OBJECTIVES
• Non-dominated: No other solution is
better than this one in all aspects.
• Pareto front: Set of all non-dominated
solutions.
Icorr London | April 8th 2021 | Matthew L. Taylor
MULTIPLE OBJECTIVE OPTIMIZATION EVALUATION
“better”
Evaluate the function many, many
times.
Each point represents the fitness of
a solution.
Icorr London | April 8th 2021 | Matthew L. Taylor
MULTIPLE OBJECTIVE OPTIMIZATION DOMINANCE
“better”
Draw lines as shown.
One solution dominates another if it
is below and left of the other
(“better” in both objectives).
The non-dominated points make the
Pareto set/front.
Dominated
Dominated
Icorr London | April 8th 2021 | Matthew L. Taylor
MULTIPLE OBJECTIVE OPTIMIZATION EVALUATION
• There are 4 non-dominated
solutions.
• Which one is optimal?
• There are trade-offs…
Pareto front:
Non-Dominated
Solutions
Dominated
Solutions
Ask an expert.
Icorr London | April 8th 2021 | Matthew L. Taylor
CASE STUDY*SEPLA CP DESIGN
• A new SEPLA (offshore suction anchor) needs a CP system for 25 years.
• Code compliant (DNV RP-B401)
• Snag-free design (flush-mount anodes only)
• Tight Schedule: Only consider stocked anodes
• Minimize cost: Anode Mass, Labor (# installs)
*Inspired by true events.
Details changed to protect the innocent.
SEPLA image courtesy Intermoor
Used with Permission
Icorr London | April 8th 2021 | Matthew L. Taylor
OPTIMIZATION METHODSEPLA CP DESIGN
Solutions
Model Outputs
(CP Design)
Design
Equations
Constants
Env. Data
OBJECTIVE
Constraint(s)FITNESS
How much
Wasted mass?
“Better”
FITNESS
How many
Installs?
“Better”
Anodes in stock
No stand-offs
La Lc W H Net Core W Core H
23 6.5 5 72 2 0.325
28 10.5 9 258 2 0.325
28 6 5.5 86 2 0.325
30 4.5 4.5 59 2 0.325
36 7 7 165 2 0.325
36 5 5 87 2 0.325
36 6 4.5 95 2 0.325
40 6 5.5 125 2 0.325
40 6.5 5.5 138 2 0.325
40 6.25 5.75 140 2 0.325
40.25 6.5 6 152 2 0.325
42 4 4 65 2 0.325
42 6 5.5 130 2 0.325
42.5 7 8 231 2 0.325
42.5 6.25 5.75 148 2 0.325
44 4 4.5 76 2 0.325
45 4.5 5.25 103 2 0.325
45.5 4.5 5 97 2 0.325
48 10.5 3.5 165 2 0.325
48 10 3.75 174 2 0.325
48 6.5 10 304 2 0.325
48 4 4 74 2 0.325
48 5 4 93 2 0.325
49 7 8 266 2 0.325
51 7 7 243 2 0.325
51.25 7 7 244 2 0.325
51.5 7 7 245 2 0.325
60 5 5.5 160 2 0.325
60 4 4 92 2 0.325
60.5 5.25 6 185 2 0.325
60.5 4 4.5 105 2 0.325
61 5.25 6 195 2 0.325
72 4.75 5.5 182 2 0.325
77 4.5 4.5 150 2 0.325
77 4.5 4 134 2 0.325
Anode catalog
Icorr London | April 8th 2021 | Matthew L. Taylor
OBJECTIVE FUNCTION RESULTSSEPLA CP DESIGN
Calculate results for all anode
geometries (solutions).
Screen out non-feasible (not
allowed) solutions.
Stand-off anodes:
Better performance, but
Not allowed by constraint.
Icorr London | April 8th 2021 | Matthew L. Taylor
SEPLA OPTIMIZATIONPARETO FRONT
There are 3 non-
dominated solutions.
Which one is optimal?
Ask an expert.
Icorr London | April 8th 2021 | Matthew L. Taylor
SEPLA OPTIMIZATIONCHOOSING THE SOLUTION
To the customer, 8 installations was
worth shedding about 4000 lbs
(1800 kg) of wasted metal from the
design.
Icorr London | April 8th 2021 | Matthew L. Taylor
CASE STUDY*ICCP RETROFIT OF 3 PLATFORM COMPLEX
• An ageing offshore complex needs an ICCP system to extend its usable life by 20 years.
• No codes for retrofit. Field Data used to calibrate model
• Buoyant Anode Sleds (4) 150 A each
• Power constraints Platform 1 can support 1 sled, Platform 2 can support 3.
• Minimize cost & handling complexity: Cable length
• Maximize Performance: minimize effects on pipelines. Fully polarize structure.
*Inspired by true events.
Details changed to protect the innocent.Icorr London | April 8th 2021 | Matthew L. Taylor
OPTIMIZATIONICCP DESIGN
A Solution
Sled Locations
Model OutputsCurrent, Potential
Distribution
Multiphysics
FEA
Constants3d models
Equipment specs
Env. Data
CP Survey Data… OBJECTIVE
Constraint(s)Exclusion Zones
Min. touchdown dist.
Max. cable length
Structure protected
FITNESS
Effect on
Pipelines
“Better”
FITNESS
Total Cable
Length?
“Better”
Minimal
Overpolarized
Stray Current
Short
Long
Icorr London | April 8th 2021 | Matthew L. Taylor
TYPICAL RESULT VISUALIZATIONPLAN VIEW EQUIPOTENTIAL
Case 82
Best for N. PL
Icorr London | April 8th 2021 | Matthew L. Taylor
RESULT VISUALIZATION “PERFORMANCE”EQUIPOTENTIAL LINES & “REMOTENESS”
Case 31:
Best for inter-platform PL
Icorr London | April 8th 2021 | Matthew L. Taylor
FINAL DESIGNSME SELECTION
Case 18:
Chosen Solution
Icorr London | April 8th 2021 | Matthew L. Taylor
FINAL DESIGNSME SELECTION
Case 18:
Chosen Solution
Icorr London | April 8th 2021 | Matthew L. Taylor
COUNTER-INTUITIVE RESULTSPIPELINE POTENTIAL PROFILES
Inter-Platform Pipeline
North Pipeline
Objective function could be
improved.
Icorr London | April 8th 2021 | Matthew L. Taylor
END
Major Thanks Due to
Sami Abu-Zahra, CP4, P.E.
for the CP FEA simulations
Icorr London
April 8th, 2021