*CONTENTSREFERENCE OF CP DESIGNED PARAMETERS

*GeneralCarbon steel/ stainless steel exposed to seawater corrosive reaction: Cathodic Protection (CP): make protected subject be a cathode of electrochemical cell.AnodicCathodic

*GeneralOffshore pipelines and subsea structures

*General

Applied standards for offshore cathodic protection design: 1- ISO 15589-2: Petroleum and natural gas industries - Cathodic protection of pipeline transportation systems- Part 2: Offshore pipelines2- DNV-RP-B401: Cathodic Protection Design.3- DNV RP F103: Cathodic protection of Submarine pipelines by Galvanic anodes.4- Norsok Standard M-503: Cathodic Protection 5- NACE-RP-0176: Corrosion Cotrol of Steel Fixed Offshore Structurea Associated with Petroleum Production.6- NACE-RP-0492: Metallurgical and Inspection Requirements for Offshore Pipeline Bracelet Anodes7- NACE RP 0387: Metallurgical and Inspection Requirements for Cast Sacrificial Anodes for Offshore Applications

*GeneralSacrificial anode (galvanic anode) Advantage: No external power required Relatively easy installationLittle chance of cathodic interference Little maintenance Less inspection and recordkeeping than with impressed current systems

Disadvantage: Not suited for media with low conductivity, e.g. in soil

*GeneralOFFSHORE CP DESIGNINPUT1- Pipeline / Structure:Material,Length, Outside diameter / AreaTemperature,Type and thickness of corrosion coating (line pipe coating, field joint coating) and weight coating,Pipe laying condition2- Deign life:3- EnvironmentResistivity, Temperature,Water depthSalinity

*The most commonly used sacrifical anode materials for offshore are:AlZn

Aluminium:

high eletrochemical capacity reduce total mass of anode (saves weight) long operating time (low consumption rate) high driving voltage

Al-Zn-In anodes most commonly used for offshoreGeneral

*Zinc:

low driving voltage low capacity (results in high weight of anodes) temperature limits < 40 Co Often used on constructions buried in mangrove mudGeneral

*General

*GeneralAluminum semi-cylindrical bracelet anode, square ended corner: flush mounted with concrete coating

*GeneralStand-off anode for jacket

*ELECTROCHEMICAL INFORMATION OF ANODE IN CP DESIGN:

Electrochemical capacityClosed circuit potentialAnode utilization factor

Suitable composition of anode material helps it meet these requirementsGeneralFacilities of bracelet anode: Inner side coating of anode Cable for anode electrical continuity

Criteria for Cathodic Protection*

Potential Criteria: Media with high salinity (offshore)maximum -800 mV, ref Ag/AgClminimum -1100 mV, ref Ag/AgCl

Media with immediate salinity (nearshore)maximum -850 mV, ref Cu/CuSO4minimum -1100 mV, ref Cu/CuSO4

*FLOWCHART OF CP CALCULATION

*REFERENCE OF CP DESIGNED PARAMETERS1/ Current densities = (Depth, Climate, pipe-environment surfaces temperature)

*REFERENCE OF CP DESIGNED PARAMETERS2/ Coating breakdown factor = (Design life, coating type)

*REFERENCE OF CP DESIGNED PARAMETERS3/ Electrochemical parameters = (Environment)

*REFERENCE OF CP DESIGNED PARAMETERS4/ Anode utilization factor = (Anode Type)

*REFERENCE OF CP DESIGNED PARAMETERS5/ Anode resistance= (Anode dimensions and environment resistivity)

*ANODE INSTALLATION & DISTRIBUTIONBRACELET ANODEAnode spacing is set at a fix number of pipe joints, limiting < 300mAnode installed post: middle of pipe (usually)Consider to install anode on the portion of pipeline near the platformSTAND-OFF ANODEMinimum distance from anodes to protective object is 300 mm.Whenever practical, anodes dedicated to CP of surfaces buried in sediments shall be located freely exposed to the sea.Anodes shall be located with 0.5 meter or more spacing between each other to avoid interaction effects that reduce the useful current output.No anodes shall be located for welding to areas with high fatigue loads.

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