CorrosionDOE-HDBK-1015/1-93SPECIALIZED CORROSIONRev. 0CH-02Page 35Where the rate of steam generation (boiling) is high, it is more difficult to eliminate theproblem of solute concentration in regions of the boiler. Caustic stress corrosion mayconcentrate in such regions as the water evaporates rapidly, but sufficient concentrationof caustic by such a mechanism to induce stress cracking is considered unlikely.Available data indicates that caustic concentrations greater than 10,000 ppm, andprobably up to 50,000 ppm, are required to induce caustic stress cracking (40,000 ppmNaOH is equivalent to 40 grams per liter or 1 mole per liter). The pH of such a solutionis on the order of 14. An alkaline environment is produced and controlled by use of asolution having some properties of a buffer, that is, one that tends to retard or slow areaction or tends to force it in one direction or the other.
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