NSTM CH 633

Question 1

What advantages do aluminum anodes offer, both physical & electrochemical?

Answer 1

Much lower consumption rate than magnesium, zinc, or iron, resulting in a 30% longer service life

Aluminum anodes weigh significantly less

Do not install over bare metal
Do not paint the anode

Question 2

What is the half cell potential for?
Zinc
Aluminum
Low Voltage Aluminum (Gallium Alloy)
Magnesium

Answer 2

Zinc - Negative 1.04VDC
Aluminum - Negative 1.06V
Low Voltage Aluminum - Negative .8 to .85 VDC
Magnesium - Negative 1.55VDC

Question 3

Should zinc anodes be installed over bare metal?
What is the preferred method of attachment?
When would Bolt-On anodes be used?

Answer 3

No, apply the surface coating system before the zinc anode is installed

Weld on, because of the secure electrical and mechanical attachment

Bolt-On is used if periodic maintenance and replacement is to be done without use of an industrial facility

Question 4

What anode is effective in polarizing steel or aluminum surface?

Answer 4

Zinc Anodes

Question 5

What are common anodes materials used to protect steel alloys?

Copper?

Answer 5

Steel- Magnesium, zinc, aluminum are common material

Copper- Iron

Question 6

For anodes what does their 3 letter designation mean

First
Second
Third

Answer 6

First - Anode Material
Second - Designates shape or general use
Third - Designates core

Question 7

What "MIL" spec is each anode? 
Iron
Low Voltage aluminum
Zinc
Aluminum
Magnesium

Answer 7

Iron - MIL-A 19521
Low Voltage - MIL-A-24779
Zin- MIL-A-18001
Aluminum - MIL-A-24779
Magnesium - ASTM B43

Question 8

How is growth cleaned on an impressed current cathodic protection system anode?

Answer 8

By hand with a wooded or plastic scraper & white or green abrasive hand pads

Don’t damage the glass reinforced plastic (GPR) holder & the platinum coated wire rod

Question 9

Aluminum anodes on Navy Ships or Submarines conform to the requirements in ..

Answer 9

MIL-A-24779

Question 10

Type ZEP anodes procured with a 3/8 inch NPS pope coupling core. How are they installed?

Answer 10

Can be installed by;

• Welding a 3/8 inch NPS pipe nipple to the attachment point & threading the anode on the pipe nipple
• Slip the pip coupling core over a 1/2 inch weld stud and bolting the anode in place

Question 11

How do you attach an anode to an aluminum surface?

Answer 11

• With aluminum studs, CRES star type lock washer and CRES locknuts
• Apply anti-seize to threaded surfaces of the studs

Question 12

For anode attachment on steel surfaces what shall the studs and nut be fabricated from?
How do you install anode?

Answer 12

Medium or Mild Steel, Galvanized Steel or Corrosion Resistant Steel

• Apply anti-seize compound to studs
• Install Z Star type lock-washers
• 1 between the nut and anode strap and 1 between the anode strap and the structure

Question 13

When would magnesium anode be used?

Answer 13

• Not in salt water
• Not on aluminum alloy surfaces
• Not in enclosed spaces without proper ventilation
• They require use of dielectric shields
• Use fresh water where the resistively is greater than 500 EM

Question 14

Why were low voltage aluminum anodes (gallium) developed?

Answer 14

To provide cathodic protection to materials that are susceptible to hydrogen embroilment at zinc and aluminum operating potentials