Why do we use sacrificial anodes in heat exchangers?
Sacrificial anodes play a vital role in preventing galvanic corrosion of tubes, tube sheets and shell of heat exchanger by consuming themselves. Regular inspection and replacement of anodes are part of preventive maintenance strategy. Anode shall be replaced if consumed more than 50%.
Why do sacrificial anodes provide protection against galvanic corrosion?
Sacrificial anodes are used to protect metal structures from corroding. Sacrificial anodes work by oxidizing more quickly than the metal it is protecting, being consumed completely before the other metal reacts with the electrolytes.
Which is used as sacrificial anode in controlling galvanic corrosion?
The materials used for sacrificial anodes are either relatively pure active metals, such as zinc or magnesium, or are magnesium or aluminum alloys that have been specifically developed for use as sacrificial anodes.
What is sacrificial anode used in heat exchangers made of?
They are made from a metal alloy with a more “active” voltage (more negative electrochemical potential) than the metal of the structure. The difference in potential between the two metals means that the galvanic anode corrodes, so that the anode material is consumed in preference to the structure.
What is the purpose of sacrificial anode?
Sacrificial anodes are metals or alloys attached to the hull that have a more anodic, i.e. less noble, potential than steel when immersed in sea water. These anodes supply the cathodic protection current, but will be consumed in doing so and therefore require replacement for the protection to be maintained.
Why is zinc used as a sacrificial anode?
These type of materials are known as sacrificial anodes because they release electrons, causing the slow corrosion of the anode in place of the actual metal in use, which is less negatively charged. Zinc make a great choice for a sacrificial anode because it’s a highly active metal that is capable of being sacrificed.
How does sacrificial protection prevent corrosion?
Sacrificial protection is the protection of iron or steel against corrosion by using a more reactive metal. Pieces of zinc or magnesium alloy are attached to pump bodies and pipes. The protected metal becomes the cathode and does not corrode. The anode corrodes, thereby providing the desired sacrificial protection.
Why is magnesium used as a sacrificial anode?
Chemically, magnesium is oxidation resistant and this is because of its surface is covered with a thin layer of oxide which protects it from being vulnerability to air. This is why it is highly suitable for use in sacrificial anodes to limit the effects and susceptibility of other metal surfaces to corrosion.
What are sacrificial anodes made of?
Sacrificial anodes generally come in three metals: magnesium, aluminum, and zinc. Magnesium has the most negative electropotential of the three (see galvanic series, right) and is more suitable for on-shore pipelines where the electrolyte (soil or water) resistivity is higher.
Which is better zinc or aluminum anodes?
Driving voltage: Aluminium anodes has a relatively high driving voltage. This means that it provides better distribution of the current, compared with zinc. Environment: Aluminium anodes carry a better environmental footprint than zinc anodes.
What is the main disadvantage of sacrificial protection?
Disadvantages include: Periodic replacements of the anode. Increased noise level from the anodes. Current output cannot be regulated.
Which metal acts as a sacrificial anode?
Magnesium or zinc metal is used as sacrificial anode for the prevention of corrosion of iron metal. Mg or Zn is oxidized instead of Fe.