zero resistance ammetry corrosion monitoring

Zero Resistance Ammetry:

In the ZRA technique, a macrocell current is measured between two corrosion sensor elements. It is obviously a useful technique to measure the magnitude of galvanic current flow between different materials or different microstructures of the same material. Preferential weld corrosion has been measured with ZRA.

Perhaps somewhat surprisingly, the measurement of macrocell current has also been applied to identical sensor elements, as a basic indicator of corrosion severity. Such measurements are mainly relevant to detecting the early stages of the breakdown of passivity and the early stages of corrosive attack. For reinforcing steel (rebar) in concrete, this principle has been adopted in the ASTM G102 test procedure and also in a rebar corrosion monitoring system.

Consider two identical probe elements. When both elements are passive, the macrocell current will be negligible. A macrocell current will tend to develop when surface passivation breaks down on one of the sensor elements. Even if passivity is lost on both sensor elements, a macrocell current may still be registered when the degree of corrosive attack is not be the same on both elements.

References/Literature:

ASTM G102 Standard: "Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements", American Society for Testing and Materials, Philadelphia, PA.

P. Schiessl and M. Raupach: "Macrocell Steel Corrosion in Concrete Caused by Chlorides", Second CANMET/ACI International Conference on Durability of Concrete, Montreal, 1991, pp.565-583.

N.S. Berke et al.: "Comparison of the Polarization Resistance Technique to the Macrocell Corrosion Technique", in ASTM STP 1065 Corrosion Rates of Steel in Concrete, 1990, pp.38-51.

T.G. Walsh: "Continuous On-Line Weld Corrosion Monitoring for the Oil and Gas Industry", International Conference on Pipeline Reliability, CANMET, Ottawa, 1992, pp.17-1 - 17-7.

Links: