Executive Summary

This document is the User Manual for Corrosion Djinn, a software package and SaaS tool, developed and released by Corrdesa LLC, for predicting the galvanic corrosion rates between mixed metals, alloys, and other conductive materials in electrolytes. Typically, the impact of galvanic corrosion is assessed on the basis of a galvanic series ¹ which are cited in a number of proprietary guidelines or public/military standards, such as;

• ASM Metals Handbook 13A
• ASTM G82
• AD823185
• DEF-STAN 00-970
• MIL-STD-889 B & C & D
• MIL-STD-1250
• MIL-DTL-14072
• NASA/TM-2019-218194

This type of classification of metals and alloys, although it provides quite useful indication of general trend in galvanic corrosion, however it does not help much to understand the actual process of galvanic corrosion when dissimilar metals are coupled since the electrochemical potential series is obtained for individual metals under “uncoupled” condition ²³⁴. The electrode potential on these galvanic series is a measure, under certain fixed conditions, of the thermodynamic tendency of a metal to undergo a corrosion reaction or lose an electron providing no information concerning the kinetics of the corrosion reaction. The magnitude of galvanic corrosion depends not only on the potential difference between dissimilar metals but also on the electrochemical kinetic parameters on each material, electrolyte composition and temperature when they are coupled together. In order to capture the kinetics, one would need the polarization behavior of each material involved. This is explained in the following sections. The military standard, MIL-STD-889C ⁵ has already started to recognize the shortfall of the present method. Appendix B of MIL-STD-889C states that the maximum corrosion current is identified by the crossing point of the material polarization curves. An issue however, is that the present form of MIL-STD-889C does not include polarization curve data. Indeed, the present standard does not even include galvanic potential data on many modern materials.

A revised version of the standard, MIL-STD-889D, was released in the first quarter of 2021 and ushered in a new era where galvanic corrosion risk will be assessed through the application of polarization data, consequently, the methodology employed in Djinn® is compliant with this revised military standard.

Corrosion Djinn addresses these issues by providing an easy to use, computerized method for determining the crossing points, together with a database of consistent, accurate, modern polarization curves – the data of which has been acquired by following a measurement protocol developed by NAVAIR. Consequently, the Djinn Platform can provide a more accurate insight into possible corrosion rate and consequent risk. The methodology used in this software is based on the mixed potential theory of electrochemistry that was first formulated 70 years ago and has been validated and used by electrochemists ever since. It is based on the principle that the common potential reached by two dissimilar materials in electrical contact, and the galvanic current between them is determined by the crossing points of their polarization curves.

References