Inhibition of Stress Corrosion Cracking of Type 403 Stainless Steel in Sodium Sulfate Solutions

The effect of various organic and inorganic compounds in Inhibiting the stress corrosion cracking (SCC) of Type 403 stainless steel in 0.01 M Na₂SO₄ solution at 100 C has been Investigated. Polarization measurements were conducted in the absence and in the presence of various potential inhibitors, such as sodium silicate, sodium phosphate, sodium nitrite, sodium sulfite, sodium cyanide, sodium chromate, hexylamine, cyclohexylamine, morpholine, and octadecylamine. Times to failure of round tensile specimens, as determined using the slow strain rate technique, were measured in 0.01 M Na₂SO₄ solutions with and without the inhibitors at an applied potential of + 540 mV_H Sodium silicate was found to be the only effective Inorganic inhibitor, and a failure time equivalent to that in air was found with the addition of 0.28M Na₂SiO₃. Hexylamine, cyclohexylamine, morpholine, and octadecylamine were also effective in Inhibiting the SCC of Type 403. Their Inhibiting efficiencies on a molar concentration basis were as follows:

octadecylamine>cyclohexylamine≈hexylamine>morpholine

The critical concentration of octadecylamine necessary to retard the SCC of Type 403 stainless steel was found to be much less than those for hexylamine, cyclohexylamine, and morpholine.