Cathodic Protection Design For Offshore Pipeline and Subsea Structure
Cathodic Protection Design For Offshore Pipeline and Subsea Structure
Cathodic Protection Design For Offshore Pipeline and Subsea Structure
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CONTENTS
1 GENERAL
3 FLOWCHART OF CP CALCULATION
Anodic Cathodic
3
General
Methods of
Cathodic
Protection
SACP: ICCP:
GALVANIC IMPRESSED
ANODE CURRENT
SYSTEM
Offshore
pipelines
and subsea
structures
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General
5
General
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General
OFFSHORE CP DESIGN
INPUT OUTPUT
1- Pipeline / Structure:
• Material,
• Length, Outside diameter / Area
• Temperature, 1-Quantity of anodes
• Type and thickness of corrosion coating
2-Weight and dimensions of
(line pipe coating, field joint coating) and
anodes
weight coating,
• Pipe laying condition 3-Distribution of anode (anode
2- Deign life: spacing)
3- Environment
• Resistivity,
• Temperature,
• Water depth
• Salinity
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General
The most commonly used sacrifical anode materials for offshore are:
• Al
• Zn
Aluminium:
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General
Zinc:
9
General
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General
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General
12
General
- Electrochemical capacity
- Closed circuit potential
- Anode utilization factor
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Criteria for Cathodic Protection
Potential Criteria:
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FLOWCHART OF CP CALCULATION
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Water depth; CP Coating type;
design design life
temperature
Protected total
surface area Initial/mean/final current density Coating breakdown factor
Anode
diameter Length of anode Anode
diameter
Initial exposed surface area of anode Final exposed surface area of anode
Anode
thickness Anode
thickness
CWC
CWC
Initial anode resistance Final anode resistance
Driving voltage =
(Protection potential;
Closed circuit potential) ??? Final anode current output
Initial anode current output
Length of anode
Initial exposed surface area of anode Final exposed surface area of anode
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REFERENCE OF CP DESIGNED
PARAMETERS
2/ Coating breakdown factor = (Design life, coating type)
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REFERENCE OF CP DESIGNED
PARAMETERS
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REFERENCE OF CP DESIGNED
PARAMETERS
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REFERENCE OF CP DESIGNED
PARAMETERS
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ANODE INSTALLATION &
DISTRIBUTION
BRACELET ANODE
Anode spacing is set at a fix number of pipe joints, limiting < 300m
Anode installed post: middle of pipe (usually)
Consider to install anode on the portion of pipeline near the platform
STAND-OFF ANODE
Minimum 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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LOGO
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