Anodes Flashcards
Galvanic anodes are permitted to mandatory dry-dock inspection at or less than how many years?
3 years.
Can you use magnesium anodes in sea water?
No, because of rapid loss of anode material and overprotection to the structure due to high driving voltage and low resistivity.
Sacrificial anodes are marked with a _____ letter designation.
3
What types of anodes can NOT be used in salt water?
Magnesium
Magnesium anodes are used in what type of water? Greater than ______ ohm/cm.
Brackish or fresh water. Resistivity of the electrolyte is relatively high, greater than 500 ohm/cm.
Aluminum anodes have a ____% service life.
30%
Can magnesium anodes be used on aluminum hulls?
No, aluminum is subject to deterioration by both acid and basic solution.
On steel surfaces, what type of lockwashers should be used?
Two star-type washers.
Where velocity exists, at least _______ the number of zinc anodes calculated for quiscent areas shall be installed.
Twice
What determines the frequency of an inspection?
Is the inspection surface or underwater, what is the expected rate of deterioration/damage?
All surface ships that are not protected by an impressed current system shall be protected by what?
Galvanic anodes, located amidships and aft.
Install twice as many anodes in velocity conditions greater than how many knots?
5 knots
With whose authority can you use magnesium on aluminum hulls?
NAVSEA
Copper alloys are known to benefit from the presence of ____ ____ in the water.
Iron ions
Reference electrodes are generally located on each side of the hull approximately ____ ____ between anode sites.
Half way.
A reference electrode is a silver/silver ____ type constructed of a silver mesh screen that has been treated with silver ______.
Chloride.
Sacrificial anodes on exterior on hull and appendages directed having _____ to _____ year cathodic protection.
2-3 year
Are galvanic anodes permitted on small boats?
Yes. ICS is not feasible.
What is the preferred install method of anodes?
Weld-on.
When are bolt-on anodes used?
If periodic maintenance and replacement is done without use of industrial facility.
Iron alloys have been used as anodes to enhance corrosion resistance of what alloys?
Copper
How often are reference electrodes usually replaced?
10-12 years.
Each seachest or other area of dissimilar metal found in larger aluminum huls. Place anode within ______ feet of dissimilar metal junction.
2 feet.
Can magnesium anodes be used on aluminum hulls?
No
Magnesium anodes have a half cell potential at approximately negative _____ volts.
1.5 volts seawater.
Is there a hazard using magnesium anodes?
Yes
On Aluminum surfaces, what type of lock washers should be used?
CRES Star type lockwashers and CRES Locknuts. Apply anti-seize to threaded surfaces of the studs.
Is a dielectric shield needed with zinc anodes?
No due to low voltage; however zinc anodes will not be installed over bare metal.
Are anode surfaces ever painted?
No, apply coating system before zinc anodes are installed.
When using aluminum anodes, you must seek guidance from who?
NAVSEA
Stagnant areas or areas subject to low velocity flow conditions (under ____ knots) shall be provided with _____ square feet of anode surface for each ______ square feet of bare metal surface.
Under 5 knots, 1sqft, 50sqft
What are common sacrificial anode materials for cathodic protection systems.
Magnesium, zinc, aluminum.
The threshold for a ship installed with an ICS is what percent?
10%
Anodes of appropriate type shall be installed at ______ of dissimilar metals, bilge pump, strainers, valves and piping that are immersed in or frequently flooded with seawater (more than 25% of the time)
Junctions
Metal that is listed in the galvanic series as more Electro (neg/pos) than another may provide cathodic protection for the more electro (neg/pos) metal. This is the basis for anode cathodic protection.
Negative (or active) Positive (noble).
Can sacrificial anodes be used on a tank interior?
Yes
What is the half cell potential for Zinc?
Negative 1.04VDC
What is the half cell potential for Aluminum?
Negative 1.06V
What is the half cell potential for Low-voltage aluminum?
Negative .8 to .85 VDC
What is the half cell potential for Magnesium?
Negative 1.55VDC
What anode is effective in polarizing steel or aluminum surfaces?
Zinc
For anode attachment on steel surfaces what shall the studs and nut be fabricated form?
Medium or mild steel, galvanized steel, or corrosion resistant steel.
When would a magnesium anode be used?
In fresh water where resistively is greater than 500 ohm.
Never in enclosed spaces. Never on aluminum alloy surfaces. Never in salt water.
Why were low voltage aluminum anodes (gallium) developed?
To provide cathodic protection to materials that are susceptible to hydrogen embrittlement at zinc and aluminum operating potentials.
What do the 3 letters on a sacrificial anode designate?
1: Metal type
A: Aluminum, L: Low voltage aluminum, Z: Zinc
2: Shape or use
3: Core
What are the platinum anodes, used in ICS and surrounded by dielectric shields?
Tantalum anodes
On steel hulls: In the midships area, install ___% of the calculated quantity of anodes for full protection.
60%
Steel hull: In the stern area, ___% of anodes necessary for the complete hull system shall be butted end to end.
40
Each bilge compartment in which seawater is held more than ____% of the time SHALL have cathodic protection.
25%
Any anode showing ____ or greater deterioration should be replaced.
50%
