Module 2 Part 2: ICCPS and Sacrificial Anodes

What does ICCP stand for?

Impressed current corrosion protection

What is ICCP

• non-sacrificial anodes recessed into hull in designated locations, supplied with specific amount of DC current from control system

• current cathodically polarizes the surrounding surface to be protected and the materials used for the anodes can vary

How do ICCP systems monitor potential difference between anodes and protected surface?

• use reference cells placed on submerged steel surface

• measurement fed back to system’s control panel which then automatically calculates and dispenses correct amount of compensating current to be sent to anodes

• surface is properly protected against corrosion whilst making sure ICCP system uses energy efficiently

Why is proper protection required?

• under protection will allow corrosion to occur

• overprotection may cause paint in immediate area to blister and peel, as well as increased risk of hydrogen embrittlement of steel (especially in high strength steel)

What items play an active role in corrosion?

• propeller, shafting, rudder

How can the corrosive effect of certain items (propeller, shafting and rudder) be reduced?

• short-circuiting them directly to hull

• rotating shafts done with a slip-on ring and graphite brushes

• rudder and other appendages supplied with earth straps thus connecting them to hull

  • thus can be protected by ICCP system ensuring all surfaces are cathodic compared to anodic

Parts of a typical ICCP system

• number of anodes (depends on protection required)

• reference electrodes

• control panel

  • power supply

What gas do ICCP systems produce? Where and why are they not used

• produce chlorine gas

• not used in corrosion protection of tanks due to sparking hazards and possibility of harm to personnel entering tank

Corrosion protection of seabays

• accomplished by ICCP, but different

• systems provide anti-fouling protection, produce environment unsuitable for growth

Sacrificial anodes

• replace/supplement ICCP

• installed in appropriate locations

• made of metal that is found on a lower position of galvanic series table

• various shapes and sizes to suit area being protected

• on hull, anodes are cast around steel strap welded to hull (on exterior plating, sea bays, some tanks) to provide necessary connection of anode to hull plating

• must calculate estimated wastage

• as anodes age and deteriorate, cover less area

Factors that play a role in the ability of sacrificial anodes to protect a surface

• possible damage to hull coating, increasing demand on anodes and wasting them away more quickly

• possible damage to one or more anode, resulting in remaining anodes being cover utilized

• possibility of anodes being completely or partially covered

• increase in stray electrical currents result in excessive wastage of anodes and causing a shortened lifespan

Noble end

Cathodic or protected

Ignoble end

Anodic or corroding end

Noble galvanic metals

• platinum, gold

• silver

• titanium

• stainless steel (passive)

• nickel (passive)

• high duty bronzes

• copper

Ignoble galvanic metals

• magnesium

• zinc

• aluminum

• aluminum alloys

• iron, steel, cast iron

• lead, tin