Galvanic corrosion testing techniques

An obvious method for studying galvanic corrosion either with or without supplementary electrical measurements is to compare the extent of corrosion of coupled and uncoupled specimens exposed under identical conditions. Such measurements may use the same techniques for estimating corrosion damage, such as mass-loss determinations, as have been described in connection with ordinary corrosion tests. 

TESTING METHODS IN GALVANIC CORROSION 6.6.1 Scanning vibrating eiectrode technique... 

The remote crevice assembly technique (see Chapter 19) is a research tool that allows one to separate the anode and cathode areas of a crevice corrosion test sample so that the current flowing between them can be measured with a zero-resistance ammeter. This technique is similar to the dual cell method, and it lends itself well to studies of microbial effects on crevice corrosion [7]. It allows direct measurement of microbial effects on both the initiation time and propagation rate for crevice attack, provided again that a suitable control experiment without the microbial influence can be done concurrently. The scime technique of separating the anode and cathode can be used to study the influence of microbes in biofilms on galvanic corrosion [li]. 

Electrochemical techniques measure electrochemical potentials and currents that are fundamentally related to the thermodynamics and kinetics of corrosion reactions. They are often used to measure the rates of uniform corrosion, to determine the tendency of localized corrosion, to study a wide range of corrosion-related phenomena such as passivation, galvanic corrosion and sensitization effects. Electrochemical corrosion testing and monitoring can be performed in a diverse range of environments in the laboratory or in the field, in a pipeline or in an autoclave. For instance, they have been successfully employed to monitor corrosion in multiphase oil/water conditions with as little as 1-2% water " ... 

Other DC methods that are quite simple to use and provide important information to the corrosion scientist include polarization resistance (ASTM G 59, Practice for Conducting Potentiodynamic Polarization Resistance Measurements), potentiostatic and potentiodynamic polarization measurements (ASTM G 5, Standard Reference Test Method for Making Potentiostatic and Potentiodynamic Anodic Polarization Measurements), cyclic polarization measurements (ASTM G 61, Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron-, Nickel-, or Cobalt-based Alloys), and galvanic current monitoring. These DC techniques can be used to estimate the reactivity of a mateiieJ in a peurticular environment, to determine the corrosion rate of a materieJ in a particular environment, and/or to determine the susceptibility of a material to localized corrosion. 

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