Investigating accelerated corrosion in SL-Tiger's box coolers and sea chests, our engineers found that box coolers were often left uncoated — allowing coating breakdown over time — while sea chests, though generally coated, still carried real corrosion risk. The analysis assumed bare steel as the worst-case scenario, and identified inadequate cathodic protection as the underlying cause of the accelerated corrosion observed.
Design calculations were carried out against a 100 mA/m² current density assumption for bare steel and a 5-year system life. For the sea chest — with a surface area of approximately 18 m² (2500 × 2500 × 550 mm) — calculated current demand came to 4.5 Amps, requiring approximately 98.5 kg of aluminium anode material.
Six 16.5 kg aluminium long flush-mounted anodes per sea chest were specified. At an anode capacity of 2357 Ah/kg and a utilisation factor of 0.85, initial current capacity was calculated at approximately 6.7 Amps, falling to approximately 5.6 Amps at end of life — comfortably above the 4.5 Amp demand throughout the design life. Anode resistance was calculated at 0.223–0.266 ohms, and the full design validated against international CP standards.
The technical analysis demonstrated a real cathodic protection deficiency in the vessel's original design. A corrective anode plan tailored specifically to the box coolers and sea chests was issued, delivering a validated 5-year protection life through optimised anode placement — engineering analysis and a designed solution, not just anode supply.
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