"Corrosion of Carbon Steel in Hot NAOH etchant"

Question:

"We have a chemical milling process which uses 20% Naoh at 104 deg C as the etchant. The etchant is circulated through Carbon steel API.5LGrB SCH 40 seamless pipework for a period of 2hrs per day as part of a regeneration process. Could you please advise/comment on the corrosion rate in terms of mm per year and also the sutability of the pipework. What would be usefull would be a graph or chart illustrating the corrosion rate for varying temperatures and concentrations. Note. Fittings are Carbon Steel BS1640. SCH 40 But weld seamless."

Answer:

You are at risk of caustic stress corrosion cracking at your stated temperatures and caustic concentrations unless all welded components are stress relieved. As for general corrosion rates of carbon steel and other alloys in caustic solutions, please refer to our technical newsletter on this subject in the "Reference" section of our corrosion and materials website.

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