Description

Sacrificial anodes on ship hulls and ballast/cargo tanks are widely used to protect steel and preserve coatings.

Functionality

Sacrificial anodes are fitted to the ships hull causing the anodes to waste (sacrifice) instead of the hull. Read more <link til teknisk side> 

Anode design

Adequate corrosion protection by sacrificial anodes is obtained by proper anode distribution/location and satisfactory level of anode current output.

Cathwell offers design of sacrificial anodes including preparation of detailed arrangement drawings.

Aluminium versus zinc

Using aluminium anodes for cathodic protection is generally more favourable compared to zinc anodes with equal level of protection:

  • The driving voltage of aluminium anodes is higher than of zinc. Hence, the protective current distribution of aluminium anodes is better.
  • The capacity of aluminium (2,650 Ah/kg) is about 3.5 times higher than zinc (780 Ah/kg). Hence, the total required anode weight by use of aluminium is less
  • As the total weight of anode material using aluminium is less than zinc the installation and weight carrying cost for aluminium anodes are less.

Contact us (<link til kontakt oss-siden>) if you would like upgrade from zinc to aluminium anodes.

For ballast tanks adjacent to tanks for liquid cargo with flash point <60 °C there are, however, some limitations of using aluminium anodes. According to DnV Rules for Ships such tanks are considered dangerous areas. Aluminium alloyed anodes are to be so located that a kinetic energy of ≤275 J is developed in case of their losseinging or falling down. That means that an aluminimum anode weighing for instance 10 kgs must be located lower than 2.8 m from the tank bottom.