Galvanic Corrosion Chart
A Galvanic Corrosion Chart is a chart that contains the galvanic or electrochemical series ranks of metals according to their potential, generally measured with respect to the Standard Calomel Electrode (S.C.E.).
This Galvanic Corrosion Chart says that the "anodic" or "less noble" metals at the negative end of the series - at the right of this diagram, such as magnesium, zinc and aluminium - are more likely to be attacked than those at the "cathodic" or "noble" end of the series such as gold and graphite.
The critical point is the difference in potential of the two materials being considered as a joined pair.
A difference of hundreds of millivolts is likely to
result in galvanic
corrosion, but only a few tens of millivolts is unlikely to be a problem.
Galvanic corrosion is a localized mechanism by which metals can be preferentially corroded. This form or type of corrosion has the potential to attack junctions of metals, or regions where one construction metal is changed to another.
Frequently this condition arises because different metals are more easily fabricated into certain forms; an example might be a door frame manufactured from aluminum extrusions (aluminum extrudes extremely well into architectural sections), but with a door handle fabricated from stainless steel grades tube to exploit its higher strength and abrasion resistance.
The table below reports the Corrosion potentials in flowing sea water at ambient temperature.
The unshaded symbols show ranges exhibited by stainless steels in acidic water such as may exist in crevices or in stagnant or low velocity or poorly aerated water where Stainless Steel become active, while the shaded areas show the potentials of Stainless Steel when is in passive state.
This table is taken from: Atlas Steel Technical Note No. 7 "Galvanic Corrosion"
Galvanic corrosion is a function of several different factors that need to be carefully evaluated when assessing the likelihood to have galvanic corrosion.
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