Cathodic Protection of Marine Vessels/Катодная защита морских судов

Издание на английском языке
Protective coatings are the most efficient way to protect ship steel structures from corrosion. However, cathodic protection, often in conjunction with protective coatings, is also used to protect immersed parts of bare steel surfaces (including coating damaged areas) from corrosion. This includes the external hull surface and the internal surfaces of tanks, such as ballast tanks. Cathodic protection (CP) can be Impressed Current Cathodic Protection, Galvanic Anode Cathodic Protection, or a combination of both. Cathodic protection controls corrosion by supplying direct current to the immersed surface of the structure, thus making the structure a cathode of a cell. The external hull of a ship is exposed to different waters with differing chemistries, which have a profound influence on the cathodic protection.
This short text on Cathodic Protection of Marine Vessels was developed to provide guidelines for ship cathodic protection design, installation, and maintenance given it is a common practice for a ship to have cathodic protection systems installed during its new construction.

Contents
1 General
1.1 Scope
1.2 Materials
1.3 Personnel
1.4 Normative References
1.5 Terms and Definitions
2 Design Criteria and Recommendations
2.1 General
2.2 Design Life of Cathodic Protection Systems
2.3 Cathodic Protection Potential
2.3.1 Cathodic Protection Potential Criteria
2.3.2 Detrimental Effects from Cathodic Protection
2.3.3 Potential Measurements
2.3.4 Reference Electrode
2.3.5 Factors Affecting Cathodic Protection Potential
2.4 Design Current
2.4.1 General
2.4.2 Structure Subdivision and Surface Area Calculations
2.4.3 Design Current Density for Bare Steel
2.4.4 Design Current Density for Coated Steel
2.4.5 Current Demand
2.5 Circuit Resistance
2.6 Anode Resistance Calculations
2.6.1 For Slender Anodes Mounted at Least 0.3 m (11.8 in) Offset from the Structure Steel Surface
2.6.2 Long Flush Mounted Anodes on the Structure Steel Surface Where Length > 4 x Width
2.6.3 Short Flat Plate Mounted Flush on the Structure Steel Surface Where Length <4 x Width
2.7 Anode Current Output and Operating Life
2.7.1 General
2.7.2 Service Temperature Effect
2.7.3 Minimum Net Weight of Anode
2.7.4 Anode Life
2.7.5 Anode Resistance at the End of Life
2.8 Cathodic Protection Systems
2.8.1 General
2.8.2 Cathodic Protection System Selection
2.8.3 Installation Consideration
2.9 Electrical Continuity
2.9.1 General
2.9.2 Shaft Ground Assembly
2.9.3 Rudder (and Other Appendages) Ground
3 Galvanic Anodes System
3.1 General
3.2 Design Considerations
3.3 Electrochemical Properties of Anodes
3.3.1 General
3.3.2 Material Chemical Composition
3.3.3 Potential
3.3.4 Current Capacity
3.3.5 Anode Consumption Rate
3.4 Anode Materials and Their Properties
3.4.1 General
3.4.2 Zinc Anodes
3.4.3 Aluminium Anodes
3.4.4 Magnesium Anodes
3.5 Anode Arrangement
3.5.1 Anode Connection
3.5.2 Anode Distribution on Hull
3.5.3 Anodes Near the Bow
3.5.4 Anodes at the Stern
3.5.5 Protection for Propellers and Shafts
3.5.6 Anodes for Rudders
3.5.7 Anodes for Sea Chests and Scoop Openings
3.5.8 Cathodic Protection of Heat Exchangers, Condensers, and Tubing.
3.6 Cathodic Protection of Internal Tanks
3.6.1 General
3.6.2 Protective Current Density
3.6.3 Anode Selection and Weight
3.6.4 Arrangement of Anodes
3.6.5 Anode Attachment
3.6.6 Coating
3.6.7 Lay-Up Period
3.7 Installation of Galvanic Anodes
4 Impressed Current System
4.1 General
4.2 ICCP System Components
4.2.1 Transformer Rectifier Power Source, Monitoring, and Control Systems
4.2.2 Anodes
4.2.3 Reference Electrode
4.2.4 Wiring and Connections
4.2.5 Stuffing Tube(s)
4.2.6 Cofferdams
4.2.7 Dielectric Shield
4.2.8 Arrangement of Anodes and Reference Electrodes
4.3 Considerations
5 Commissioning, Operation, and Maintenance
5.1 General
5.2 Potential Measurement
5.3 Commissioning: Galvanic Systems
5.4 Commissioning: Impressed Current Systems
5.4.1 Visual Inspection
5.4.2 Pre-energising Measurements
5.4.3 Initial Energising
5.4.4 Performance Assessment
5.5 Operation and Maintenance
5.5.1 General
5.5.2 Galvanic Anode Systems
5.5.3 Impressed Current Systems
5.6 Drydocking Period
5.7 Fitting Out and Lay-Up
5.7.1 General
5.7.2 Fitting-Out Period
5.7.3 Lay-Up Period
5.8 Stray Current
5.9 Interaction Testing
6 Documentation
6.1 General
6.2 Galvanic Anode Systems
6.3 Impressed Current Systems
Bibliography