permanent cathodic protection monitoring systems for ...€¦ · • the baker pmg – cpcm...

CED Warrington - 2013

www.stoprust.com © 2013 Deepwater Corrosion Services Inc.

Permanent Cathodic Protection Monitoring Systems for Offshore Pipelines

Ross FieldingRoss Fielding

Deepwater EU Limited.Deepwater EU Limited.

Elstead, UK.Elstead, UK.



Presentation Outline

•• Limitations of existing Limitations of existing methodsmethods

•• Do we need Do we need ““Close Close Interval Potential Interval Potential SurveySurvey”” offshore?offshore?

•• Improved inImproved in--line toolsline tools

•• Subsea CP test stationsSubsea CP test stations

•• Future surveillance Future surveillance optionsoptions



Limitations of Existing Methods

•• Must have periodic pipeline Must have periodic pipeline contact to recontact to re--calibrate (every 5 calibrate (every 5 --10 Kms max).10 Kms max).

•• ExpensiveExpensive–– Need ROV, RSV, GPS, Need ROV, RSV, GPS,

Bathymetry, Pipe Track, CP Bathymetry, Pipe Track, CP Equip, PeopleEquip, People

•• UnreliableUnreliable–– Many error sourcesMany error sources

–– Hard to assure repeatabilityHard to assure repeatability

•• Surveys that do not reSurveys that do not re--calibrate are meaninglesscalibrate are meaningless



Typical Survey Data



Typical Survey Data (3 Electrode Survey)

Less than 10 mV potential spread over 3 Kms.This is typical of virtually all offshore pipelines.2 data points over this section could have defined condition.



Do we need “Close Interval Potential” data on Offshore Pipelines?

•• The answer is NO. The answer is NO. –– We could accurately define pipeline CP performance We could accurately define pipeline CP performance

range with a data point every 5 range with a data point every 5 --10 Kms. If that data point 10 Kms. If that data point were totally repeatable.were totally repeatable.

–– Attenuation modeling could predict worst case between Attenuation modeling could predict worst case between two points.two points.

•• In FactIn Fact–– The contact readings on any The contact readings on any ““close Interval Potential close Interval Potential

Survey (CIPS)Survey (CIPS)”” are used to anchor the reported profile on are used to anchor the reported profile on all methods, the data between the contacts is somewhat all methods, the data between the contacts is somewhat superfluous.superfluous.



Attenuation Calculation Output

0 1000 2000 3000 4000 50000.8

0.86

0.93

0.99

1.05

Distance Along Pipeline (Feet)

CP

Pote

ntia

l Atte

nuat

ion

(-V

olts

AgC

l)

AP

.8

CP x( )

L0.000 x



Improved In-Line Tools

•• The Baker PMG The Baker PMG –– CPCM (Cathodic Protection Current CPCM (Cathodic Protection Current Mapping) Tool has been used on offshore retrofitted lines and Mapping) Tool has been used on offshore retrofitted lines and clearly shows anode sled locations.clearly shows anode sled locations.

•• This method of monitoring is unThis method of monitoring is un--ambiguous, the current flow ambiguous, the current flow can be calibrated to a current density, and a few external can be calibrated to a current density, and a few external potential reference points to fully define CP systempotential reference points to fully define CP system



RetroSled Being Installed



Typical CPCM Chart at RetroSled



Why Are Spaced Test Points Acceptable?

•• Onshore CP used Test Stations until problems were Onshore CP used Test Stations until problems were noted as follows:noted as follows:–– IR Errors from mainly ICCP systemsIR Errors from mainly ICCP systems

–– Induced ACInduced AC

–– Short range resistivity changesShort range resistivity changes

–– Stray Current interference from other DC sources (DC Stray Current interference from other DC sources (DC Traction, other ICCP Systems etc)Traction, other ICCP Systems etc)

•• Because of these issues CIPS was introduced in Because of these issues CIPS was introduced in the early 1980the early 1980’’s, and became SOP by early 90s, and became SOP by early 90’’s.s.



Why Spaced CP Test Stations Are Valid Offshore

•• No IR Errors No IR Errors –– virtually virtually no ICCP on offshore no ICCP on offshore lineslines

•• No AC interference No AC interference –– no no overhead power lines or overhead power lines or ROW sharingROW sharing

•• No shortNo short--range range resistivity changesresistivity changes

•• No DC traction systems, No DC traction systems, or sources of stray or sources of stray current interferencecurrent interference

•• No problem sampling at No problem sampling at 55--10 km intervals10 km intervals



Subsea CP Test Station Components

•• Permanent Reference Permanent Reference ElectrodeElectrode

–– Use dual electrode (Zn / AgUse dual electrode (Zn / Ag--AgCl) for calibrationAgCl) for calibration

•• Reference Ground Connection Reference Ground Connection to Pipeto Pipe

–– Made with RetroClamp which Made with RetroClamp which also mounts the electrodealso mounts the electrode

•• Voltage Display Voltage Display –– Reads the reference electrode Reads the reference electrode

potentialspotentials

•• Redundant Stab PlateRedundant Stab Plate–– Separate stab plate for backSeparate stab plate for back--

up, particularly important on up, particularly important on buried pipelinesburied pipelines



Reference Electrodes

•• Several Manufacturers.Several Manufacturers.

•• Do they have InDo they have In--Situ Situ calibration or a Plan Bcalibration or a Plan B

•• Dual reference electrodeDual reference electrode–– Zinc swZinc sw

–– Ag/AgCl swAg/AgCl sw

•• 25 Year Life25 Year Life

•• Provides pipe/seawater Provides pipe/seawater potentialpotential

•• Shown direct welded to Shown direct welded to PLET SkidPLET Skid



Grounding / Mounting Clamp

•• Reference electrode Reference electrode attached to dual attached to dual clamps prior to over clamps prior to over boarding and boarding and installationinstallation–– Cable is protected Cable is protected

within a steel within a steel reinforced rubber reinforced rubber hosehose



Readout – Voltage Display

•• Light powered readout Light powered readout uses photouses photo--voltaic voltaic convertersconverters




•• Buoyant spheres for pipeline Buoyant spheres for pipeline monitoring.monitoring.



Back-Up Stab Plate

•• Provides an insulated Provides an insulated reference connection reference connection to pipeline for use with to pipeline for use with a tip contact CP Probea tip contact CP Probe



Integrated Clamp System for Deep Water Flowline Mid-Point Monitoring



Integrated Clamp System for Deep Water Flowlines



AUV Surveys – The future



Summary•• Conventional ROV mounted inspection techniques are Conventional ROV mounted inspection techniques are

expensive will be out of the market in the near futureexpensive will be out of the market in the near future

•• Permanently installed pipeline monitoring systems allow more Permanently installed pipeline monitoring systems allow more rapid, reliable assessment of pipeline CP status at a fraction rapid, reliable assessment of pipeline CP status at a fraction of the costof the cost

•• As AUVAs AUV’’s (Autonomous Underwater Vehicles) take on the role s (Autonomous Underwater Vehicles) take on the role of pipeline external inspection the visual indicators will evolvof pipeline external inspection the visual indicators will evolve e into the primary offshore CP monitoring toolinto the primary offshore CP monitoring tool

•• Many subsea pipelines are not Many subsea pipelines are not ““pigablepigable”” however, Inhowever, In--Line Line tools could carry much of the CP inspection burden on tools could carry much of the CP inspection burden on candidate pipelinescandidate pipelines

•• Acoustic Devices are being trialed, again limitations existAcoustic Devices are being trialed, again limitations exist



Presentation Finished

Thank You for Your Attention

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