When two dissimilar metals are immersed in seawater as electrolyte.
What is an Anode?
Zinc, more corrosion prone, higher driving voltage, positive charge.
What is a Cathode?
Hull, less corrosion prone, lower driving voltage, negative charge.
How does the rate of corrosion determined?
depends on potential difference, stray currents, resistivity and seawater temp.
What is a nominal resistivity of seawater at a temperature of 20 degree C or 68 degree F.
20 - 22 Ohms
How does a sacrificial anode system works?
When a more reactive metal (anode) is installed near a less reactive metal in a submerged seawater, the more reactive metal will protect the less reactive metal and sacrifice itself.
How often is the sacrificial anodes replaced?
Every 3 years
What are the 5 types of sacrificial anodes?
zinc, aluminum, magnesium, iron, and steel waster pieces
What are the characteristics of a zinc anodes?
has a half-cell, - 1.04 v, can be bolted or welded (preferred)
What are the characteristics of aluminum anodes?
currently being tested by NAVSEA
What are the characteristics of magnesium anodes?
has a half-cell, + 1.5 v, not used is seawater.
What are the characterisctics of iron anodes?
installed to increase the presend of iron in the water.
What are the characteristics of steel waster pieces?
mild steel at nonferrous metal jucntions to protect sea valves and sea chest.
What are sacrificial anodes used for?
small boats, mothballed ships, submarines, piping systems, bilge pumps, valves, ballast tanks, fuel tanks, cht, etc.
What are the advantages of sacrificial anodes?
no external power, little maintenance, easy to install, and protects at all times.
What are the disadvantages of sacrificial anodes?
current cant be controlled, water turbulence increases noise level, frequent replacement is needed with stray currents from welding.
How does an Impressed Current System works?
uses a regulated dc power to provide necessary current to prolarize the hull. Uses inert anodes of platinum-coated tantalum.
What are the components of ICS?
power supply, controler, anodes, reference electrode, stuffing tube, and shaft grounding assembly.
What is the use of the controller?
creates an output signal proportional to the voltage difference between the reference voltage (electrode-to-hull) and internally set voltage.
Where are the anode locations?
at least 5 ft below light-load waterline, 1 to 2-screw ship - 1 set located between 10 - 50 fwd of propeller, 4-screw ship - two anodes located between fwd and aft propeller planes - 1 port and 1 stbd, in a minimum water turbulence to protect from damage.
When are anodes replaced?
every 10 years of longer.
Anodes are available in what sizes?
2 ft - 40a, 4 ft - 75a, and 8 ft - 150a
Anodes are constructed with what?
2 platinum-mated tantalum rods, mounted in an insulating glass-reinforce polyester holder.
When are reference electrode replaced?
10 - 12 years
Reference electrode are constructed with what?
silver/silver chloride constructed of a silver mesh screen, treated with silver chloride.
How is reference electrode insulated from the ship?
by a polyvinyl chloride holder
What is used to pass the cable from the electrode through the hull of the controller?
How is the Shaft Grounding Assembly constructed?
consist of a silver-alloy band, ring-fitted on the propeller shaft alley.
How is the Shaft Grounding Assembly bonded to the shaft?
electrically connected from shaft to hull, using a silver-graphite brushes.
Why is the Shaft Grounding Assembly necessary?
to permit the anode current that flows through the water to enter the propeller blades and return to the hull.
How many Shaft Grounding Assembly are provided for each shaft, and with a carrier shaft or larger?
1 each shaft, 2 for each larger shafts.
How are a Rudder grounded?
by brazing a 1 1/2 braided, tinned-copper grounding strap between rudder stock and the hull
What is the purpose of Dielectric Shield?
to prevent shorting of the anode current to the hull (thick epoxy)
T/F: never energize the system if the ship is of the water
Before reference electrode is connected to the controller, reference electrode and the hull should be how many volts?
Hull and reference electrode has what charge in respect to electrical.
Hull - negative, reference electrode - positive
How many reference electrodes are installed for each controller?
What does it mean when voltage is zero?
reference electrode has an open lead or shorted to the hull
What does it mean when voltage is .6 volts or higher?
ship is receiving cathodic protection from an external source, zinc anode or electrical leakage.
What is the voltage between a disconnected platinum anode and the steel hull
1.0 - 2.0 volts
What is the voltage when anode lead is immersed in seawater?
2.0 - 5.0 volts
Hull in seawater is set at what potential?
negative .85 volt
What happens if you exceed the voltage?
it will result in hydrogen generation
What is the voltage between the hull-to-reference with an ordinary steel hull to the silver to silver chloride reference electrode?
negative .80 to negative .90
What for is used for Cathodic protection Log
NAVSEA Form 9633/1, read daily, sumbitted to NAVSEA monthly
What is the voltage when current output is 100%?
0 - 1 volt
What is the voltage when current output is 30 - 50% capacity?
.3 - .5 volts
What are the two power supplies capacities?
0 - 150A and 0 - 300A
When is PMS conducted?
Anodes must never be installed within what minimum distance from a sea chest?
Prior to connecting the anode leads to the power supply you must verify no shorts exist by using what tool?