The factors affecting pitting and cracking resistance of Type 420SS in CO 2environments are investigated. These include chloride concentration, pH, temperature, and presence of H 2S.
Potentiostatic polarization curves were used to study pitting, and constant applied potential, step stress, tensile tests were used to investigate the SSC phenomenon. The test environments were NaOH solutions saturated with CO 2.
It is found that the total bicarbonate and chloride concentrations are the two important factors controlling whether pitting will occur. The presence of small amounts of H 2S is predicted to protect against pitting by shifting the free corrosion potential cathodically. The temperature is shown to have little effect on the pitting potential, at least, in the temperature range studied (up to 90°C).
Pitting is necessary, but not sufficient, for cracking to occur. It is predicted that the factors influencing pitting in these environments will also control the cracking. The applied load, in conjunction with pitting, is also found to be an important variable.