EFFECT OF ELECTRODE POTENTIAL AND TEMPERATURE ON STRESS CORROSION CRACKING OF PIPELINE STEEL X70 IN HIGH pH SOLUTIONS

The behaviors of high pH stress corrosion cracking(SCC)of pipeline steel X70 in 0.5mol/L Na2CO3+1 mol/L NaHCO3 solution were studied by means of slow strain rate tests (SSRT) at different temperatures in the range from 30 ℃ to 65 ℃ and different electrode potentials from -1500 to -200 mV(SCE).The temperature had no apparent effect on SCC susceptibility of the steel in anodic polarization range,but the SCC susceptibility increased with the rise of temperature in cathodic polarization range.The SCC susceptibility of the steel increased generally with decreasing the potential.When potential E≤EH,the equilibrium potential for hydrogen discharge (H2＝2H+＋2e) in the solution,it should be hydrogen induced cracking (HIC) which dominates the cracking process.On the contrary,anodic dissolution should dominate the cracking process when E>EH.