Study on Electrochemical Pitting Corrosion of 316NG and 321SS for Primary Pipes in Simulated Marine Atmosphere Environment

The pitting corrosion of 316 NG stainless steel and 321 stainless steel in the 3.5% Na Cl solution was studied by using the electrochemical polarization curves and electrochemical critical pitting temperature test. The results showed that the pitting potential of 316 NG was markedly higher than that of 321 at all the test temperatures（room temperature, 40℃, 60℃ and 80℃）. The pitting potential of 316 NG and 321 dropped sharply when the test temperature increased, which demonstrated that the pitting resistance became worse. The critical pitting temperature（CPT） of 316 NG and 321 were 20.1℃ and 3.9℃ respectively. From the perspective of electrochemistry, the pitting corrosion resistance of 316 NG was apparently better than that of 321 in the simulated marine environment. The particles of Ti N or Ti C could be observed in the corrosion pits by using scanning electron microscopy（SEM）, which led to a decrease of the pitting resistance.