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Galvanic corrosion can be defined simply as being the effect resulting from contact between two different metals or alloys in a conducting corrosive environment. Another term employed is galvanic coupling. When a metal is immersed in any electrolytic solution, it is possible to measure its dissolution natural corrosion.
For each solution, it is possible to establish a "galvanic series", that is, a ranking of different metals and alloys as a function of this measured potential.
When two different metals or alloys immersed in the same solution are joined together electrically, an electric current will be set up between them, resulting from the short circuit created. The coupling potential must of necessity lie between the two potentials for the uncoupled metals and an increase in corrosion is generally observed in the less noble alloy and a decrease or suppression of corrosion in the more noble material.
Due to modifications in the electrolyte, inversions may occur in the potential series. Thus, zinc covered with corrosion products can become more "noble" than iron in certain hot waters problem encountered in domestic hot water tanks ; tin can become less "noble" than iron in organic acid solutions problem encountered in food cans.
For a given current between two different metals, the current density, and hence the rate of dissolution of the less noble metal anode, will be greater the smaller the surface area S A of the anode.
The use of unfavourable surface area ratios has led to many expensive and often spectacular failures. Some Means of preventing galvanic corrosion : choose metal combinations in which the constituents are as close as possible in the corresponding galvanic series, avoid an unfavourable surface area ratio. Wherever possible, use a seal, insulator, coating, etc.
Back Galvanic series for various conducting materials in seawater water velocity 2. The potential is expressed with respect to a saturated calomel reference electrode. The blue cells indicate the potentials in the active state for passivatable metals. Galvanic corrosion between a copper tube and copper-phosporus braze in the brazing region.
Galvanic Corrosion Testing
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Galvanic corrosion can be defined simply as being the effect resulting from contact between two different metals or alloys in a conducting corrosive environment. Another term employed is galvanic coupling. When a metal is immersed in any electrolytic solution, it is possible to measure its dissolution natural corrosion. For each solution, it is possible to establish a "galvanic series", that is, a ranking of different metals and alloys as a function of this measured potential.
Thank you for interesting in our services. We are a non-profit group that run this website to share documents. We need your help to maintenance this website. Please help us to share our service with your friends. Share Embed Donate. Copyright ASTM Standard Guide for Development and Use of a Galvanic Series for Predicting Galvanic Corrosion Performance1 This standard is issued under the fixed designation G 82; the number immediately following the designation indicates the year of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.
Historical Version s - view previous versions of standard. More G This type of accelerated corrosion is referred to as galvanic corrosion. Because galvanic corrosion can occur at a high rate, it is important that a means be available to alert the user of products or equipment that involve the use of dissimilar metal combinations in an electrolyte of the possible effects of galvanic corrosion. The metal that will suffer increased corrosion in a galvanic couple in that environment can then be predicted from the relative position of the two metals in the series. The potentials themselves versus an appropriate reference half-cell are listed so that the potential difference between metals in the series can be determined.