optimization of cp systems - icorr.org

OPTIMIZATION OF OFFSHORECATHODIC PROTECTION SYSTEMS

ICORR LONDON 8 APRIL 2021

MATTHEW L. TAYLOR, PH.D.

OPTIMIZATION

Icorr London | April 8th 2021 | Matthew L. Taylor

SECTION ONE

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


TERMINOLOGYOPTIMIZATION

• Function: The model we evaluate

• Solution : List of proposed input values

• Results : Outputs from a model for a

given set of inputs.


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.


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”


TERMINOLOGYMULTIPLE OBJECTIVES

• Non-dominated: No other solution is

better than this one in all aspects.

• Pareto front: Set of all non-dominated

solutions.


MULTIPLE OBJECTIVE OPTIMIZATION EVALUATION

“better”

Evaluate the function many, many

times.

Each point represents the fitness of

a solution.


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


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.


CASE STUDY:SACP OPTIMIZATION

SECTION ONE


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


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


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.


SEPLA OPTIMIZATIONPARETO FRONT

There are 3 non-

dominated solutions.

Which one is optimal?

Ask an expert.


SEPLA OPTIMIZATIONCHOOSING THE SOLUTION

To the customer, 8 installations was

worth shedding about 4000 lbs

(1800 kg) of wasted metal from the

design.


CP FEAICCP OPTIMIZATION

SECTION ONE


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


CP FEAMODEL CALIBRATION


SEARCH SPACEALLOWED AREAS


TYPICAL RESULT VISUALIZATIONPLAN VIEW EQUIPOTENTIAL

Case 82

Best for N. PL


RESULT VISUALIZATION “PERFORMANCE”EQUIPOTENTIAL LINES & “REMOTENESS”

Case 31:

Best for inter-platform PL


OPTIMIZATIONPARETO FRONT


OPTIMIZATIONPARETO FRONT

82

31


FINAL DESIGNSME SELECTION

Case 18:

Chosen Solution


COUNTER-INTUITIVE RESULTSPIPELINE POTENTIAL PROFILES

Inter-Platform Pipeline

North Pipeline

Objective function could be

improved.


END

[email protected]

Major Thanks Due to

Sami Abu-Zahra, CP4, P.E.

for the CP FEA simulations

Icorr London

April 8th, 2021

optimization of cp systems - icorr.org

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