Where the rate of steam generation (boiling) is high, it is more difficult to eliminate the
problem of solute concentration in regions of the boiler. Caustic stress corrosion may
concentrate in such regions as the water evaporates rapidly, but sufficient concentration
of caustic by such a mechanism to induce stress cracking is considered unlikely.
Available data indicates that caustic concentrations greater than 10,000 ppm, and
probably up to 50,000 ppm, are required to induce caustic stress cracking (40,000 ppm
NaOH is equivalent to 40 grams per liter or 1 mole per liter). The pH of such a solution
is on the order of 14. An alkaline environment is produced and controlled by use of a
solution having some properties of a buffer, that is, one that tends to retard or slow a
reaction or tends to force it in one direction or the other.