Caustic SCC of Carbon Steel in a Chemical Plant

A petrochemical plant in the Middle East was experiencing caustic stress corrosion cracking (SCC) failures of carbon steel piping in a caustic loop removing a catalyst from the process stream. The rest of the loop, also carbon steel, did not experience any failures. A sister plant in the US was experiencing no failures at all. Electrochemical testing was undertaken to identify the probable cause of the SCC. The results showed that the caustic liquor was very reducing, and the polarization curves and open circuit potentials differed for the two plant liquors. A probable cause of the SCC was identified, and some options for remedial action were suggested.