Exam Question
With reference to hull protection against corrosion describe how EACH of the following operate:
(a) Sacrificial anodes (8)
(b) Impressed current system (8)
Class 4 (4th Engineer)
SC&S
📅 Apr 2024
Reference Answer
### (a) Sacrificial Anodes (8 Marks)
#### 1. Principle of Operation
Sacrificial anode systems operate on the principle of **galvanic corrosion** to provide **cathodic protection** to the ship's hull. This electrochemical process occurs when two dissimilar metals are placed in an electrolyte (seawater). A galvanic cell is formed, and the more electrochemically active metal becomes the anode, corroding preferentially, while the less active metal becomes the cathode and is protected.
* **Galvanic Series:** The ship's hull is typically constructed of steel (primarily iron). Sacrificial anodes are made from metals such as zinc or aluminium alloys, which are higher (more anodic) in the galvanic series than steel.
#### 1. Principle of Operation
Sacrificial anode systems operate on the principle of **galvanic corrosion** to provide **cathodic protection** to the ship's hull. This electrochemical process occurs when two dissimilar metals are placed in an electrolyte (seawater). A galvanic cell is formed, and the more electrochemically active metal becomes the anode, corroding preferentially, while the less active metal becomes the cathode and is protected.
* **Galvanic Series:** The ship's hull is typically constructed of steel (primarily iron). Sacrificial anodes are made from metals such as zinc or aluminium alloys, which are higher (more anodic) in the galvanic series than steel.
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