Description. ASTM G Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. View more. ASTM G()e1. Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements. ASTM-G Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements – corrosion.
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In cases where the corrosion potential is within 50 to mV of the reversible potential of the corroding electrode, the electrochemical reactions will occur simultaneously on the electrode surface. In addition, some guidelines for converting polarization resistance values to corrosion rates are provided.
The effect of solution resistance is a function of the cell geometry, but the following expression may be used to approximate its magnitude. The error is illustrated by Eq A sample calculation is given in Appendix X5. Therefore, the alloy equivalent weight, Astk, is the reciprocal of this quantity: A superscript epsilon e indicates an editorial change since the last revision or reapproval.
NOTE 2—Mid-range values were assumed for concentrations of alloying elements. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility.
In some computerized polarization equipment, this calculation is made automatically after the specimen area is programmed into the computer. Some typical values of equivalent weights for a variety of metals and alloys are provided.
This is equivalent to the calculation shown in 4. This calculation may be expressed as follows: It is best if an independent technique can be used to establish the proper valence for each alloying element. W 5 the atomic weight of the element, and n 5 the number of electrons required to oxidize an atom of the element in the corrosion process, that is, g02 valence of the element.
Icor icor 5 A 1 where: A sample wstm is given in Appendix X2 1.
Wi 4 unless a better basis is available. In this case, the magnitude of the error is proportional to scan rate. Some approaches for estimating this information are given.
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Another approach is to measure or estimate the electrode potential of the corroding surface. Some typical values of equivalent weights for a variety of metals and alloys are provided. In general, Eq 7 and Eq 8 may be used, and the corrosion rate calculated by these two approximations may be used as lower and upper limits of the true rate.
Some approaches for estimating this information are given. A number in parentheses indicates the year of last reapproval. B5 ba bc 2.
ASTM G102 Standard Practice
The conversion of these results to either mass loss or penetration rates requires additional electrochemical information. A sample calculation is given in Appendix X1. KRT b 5 nF 9 where: For pure elements, the equivalent weight is given by: Therefore, the gram equivalents of the dissolved components are given by Eq 3. Other units may be used in this calculation. Normally only elements above 1 mass percent in the alloy are included in the calculation.
A sample calculation is given in Appendix X6. ASTM D standar It is assumed that the current distributes uniformly across the area used in this calculation. B Registered trademark Haynes International. See Refs for more information. The capacitance charging effect will cause the calculated polarization resistance to be in error.