Significance of Iron Oxide Forms 1

[Guest102023]

I'm looking at a case of internal corrosion of a steel pipe with heavy amounts of flakey scale, which was analyzed at 64% magnetite, 14% hematite, and 22% goethite (hydroxide).

The corrosion is no surprise, but I want to know the significance of the different types of iron oxide and what they say about how things developed. I am looking for general information and perhaps references as much as I am an answer to this specific problem.

Temperatures are modest (ambient temperature in MI) and there is no pressure. Air and moisture are present, and some methyl chloride also. There is also a fairly thick deposit that looks like coke (though its not from a refinery) on the bottom side, so deposit corrosion is certainly going on.

Thanks in advance.

 

[Metaljon]

The formation of magnetite by the reduction of hematite with iron in the presence of corrosion conditions takes place by two reactions : (1) the oxidation of iron metal with water, and ( 2 ) the reduction of hematite with hydrogen to form magnetite. The overall oxidation -reduction reaction is affected by temperature, pressure, and solution acidity. Looking at your results and process conditions, the high level of magnetite indicates that the corrosion processes have been on-going for some time resulting in a fairly high level reduction of hematite to magnetite.

 

[unclesyd]

In addition to the above post by Metalion you have another ion that drives the reaction towards Magnetite and that is the CL ion. Magnetite from from this type reaction is normally very dense, approaching the density of the parent metal. We have an area where there the CL ion is always present so the corrosion we get on CS is nearly all extremely dense Magnetite. The Cl ion has the same effect ion and around steel on boats. You start chipping and the all of a sudden you have nothing left.

 

[Guest102023]

Thanks to both, that's the type of 'practical implications' I was looking for. This oxide was reported as highly crystalline, which I think could be interpreted as dense.

 

[emxhps06]

Differential aeration