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how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

(OP)
HI

Recently I have encountered a problem in which my carbon steel component is heavily corroded. The component is made up of rolled plates which we recently purchased. I have done XRD analysis of the scale to see if high corrosion rate is due to rolled in scale present on the plates as heavy metal loss was observed. I have got strong peaks of magnetite and low peaks of iron(III) oxide-hydroxide such as Lepidocrocite & Goethite. I have also got halites like sodium, potassium, and Chloride. So this means that the corrosion product mainly formed due to seawater exposure as the item is being transported through sea cargo. Magnetite is usually present in the mill scale so I highly doubt that it is the mill scale presence that has caused high corrosion rate in the presence of seawater. As per my understanding of general rust without mill scale magnetite should not be detected.What you guys think?

RE: how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

Your correct in your assumption.

RE: how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

The mill scale is quite adherent while the corrosion product is loose and flaky. It is also huge in mass compared to mill scale.

RE: how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

magnetite can also be part of corrosion products and detected without mill scale

metallographic cross section may provide visual evidence of the presence of a mill scale.

water containing dissolved oxygen is very corrosive to carbon steel

RE: how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

Did you see pitting or do you have visual evidence of the metal loss?

RE: how to differentiate between corrosion product on carbon steel is corroded mill scale or just rust

I believe your first assessment (exposure to seawater, and/or salt air) is the correct one - general corrosion with some pitting may be evident.

You accepted this shipment?

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