51316-7795-FeS Nucleation on Oxide Free Mild Steel Surfaces

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Product Number: 51316-7795-SG

ISBN: 7795 2016 CP

Author: Omar Yepez

Publication Date: 2016

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The corrosion protection due to iron sulfide scales has been and continues to be a controversial issue in corrosion science. These scales are very important to understand the mechanism of sour corrosion. For example speculations about the type of iron sulfide formed and its role on localized corrosion has triggered a whole venue of investigations. However the fundamental aspects of the scale formation crystal growth and its protectiveness towards the metal are still not fully understood. Therefore it is important to investigate and understand the fundamental key issues regarding the nature of iron sulfide scale formation. The current paradigm states that mackinawite is a protective form of iron sulfide. This however has not been proven as mackinawite occurs at high pH which generally yields lower corrosion rates. This paper describes the formation of iron sulfide at different hydrogen ion concentrations different potentials and at ambient temperature. This was performed at potentials far from iron oxide formation. Even at relative high pH mackinawite was found to reduce corrosion but it was not totally mitigated. Mackinawite nucleation and crystal growth was observed as an extremely high active process which is fully consistent with this observation. This is attributed to the formation of several layers co-occurring at different nucleation rates. This process will result in a high porosity scale which will not protect the metal. This paper describes the evidence of such process