Systematic study of the corrosion properties of selected high-resistance alloys in natural seawater

Electrochemical measurements were conducted to evaluate localized corrosion on UNS S31603, UNS S31803, UNS S32750, UNS S31254 and UNS N08825 in natural seawater. Critical pitting and crevice temperatures were assessed using a potentiostatic technique and critical potentials for pitting and crevice corrosion initiation and repassivation were identified using potentiodynamic polarization at temperatures from 5 to 40 °C. Passivity breakdown always occurred through pitting and crevice growth above a transition temperature. Below this temperature, pitting corrosion was not observed on any of the alloys regardless of the applied potential, but initiation of crevice corrosion occurred after the alloys reached a transpassive potential.

► Pitting corrosion does not take place below the CPT regardless of the applied potential.
► Crevice corrosion occurs below CCT when alloys reach a transpassive potential.
► UNS S32750 and UNS S31254 have excellent resistance to crevice and pitting in seawater.
► UNS S31603, UNS N8825, and S31803 are attacked at 5, 10 and 30 °C respectively.
► Resistance to localized corrosion: UNS S32750 > UNS S31254 > UNS S31803 > UNS N8825 > UNS S31603.