Atmospheric exposure tests galvanic corrosion

The extent of galvanic action in atmospheric exposure may also be restricted by the development of corrosion products of high electrical resistance between the contacting surfaces — this is especially likely to occur if one of the metals in the couple is an iron or steel that will rust. In long-time tests such possible interruptions in the galvanic circuit should be checked by resistance measurements from time to time so as to determine the actual periods in which galvanic effects could operate. 

Galvanic corrosion testing under atmospheric exposures has been standardized and bears the titles ISO 7441-84, ASTMG 104-89 for plate tests and ASTM G116-93 for wire-on-bolt tests.21,34,35 A form of test assembly for galvanic corrosion testing is shown in Figure 2.5. 

It is occasionally desirable to evaluate galvanic corrosion effects from atmospheric exposures (see ASTM G 116, Conducting Wire-on-Bolt Test for Atmospheric Galvanic Corrosion and ASTM G 149, Conducting the Washer Test for Atmospheric Galvanic Corrosion). Several different types of sj)ecimens have been used for this purpose. One approach is... 

Three factors that are different in atmospheric testing from most other galvanic corrosion testing are the presence of a limited amount of electrolyte, the need for a very long duration of exposure, and the importaince of specimen... 

The wire-on-bolt test, described in ASTM G 116 (Practice for Conducting the Wire-on-Bolt Test for Atmospheric Galvanic Corrosion), has been used with standard materials as an atmospheric corrosivity test under the names of the CLIMAT and ATCORR tests. This test consists of wrapping a 1.0-m length of wire of the anodic material around a threaded bolt or rod of the cathodic material. Post-test evaluation is typically done by mass loss only. Since the wire diameter is much smaller than the 0.5-cm galvanic interaction distance in the atmosphere, the effective tmode-to-cathode area ratio is well below 1 1, making this a fast test. A typical exposure duration is 90 days. The short duration is... 

Standard Practice for Conducting the Washer Test for Atmospheric Galvanic Corrosion Standard Practice for Selecting and Characterizing Weathering Reference Materials Used to Monitor Consistency of Conditions in an Exposure Test... 

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