Stress Corrosion Behavior of X80 Pipeline Steel under the Combined Effect of Applied Potential and Low Strain Rate

Abstract This study investigated the stress corrosion behavior of X80 pipeline steel in NS4 soil simulation solution through slow strain rate tensile tests (SSRT) and fracture morphology observation. The results indicated that with the negative shift of applied potential, the stress corrosion sensitivity of X80 parent metal and welded joints increased. The elongation loss after fracture for welded joints was 2% to 6% higher than parent metal, and the reduction in area was 10% to 14% higher than parent metal. The fracture morphology of X80 parent metal exhibited cleavage fracture at -1300 mV (vs. CSE), while the welded joints showed cleavage fracture at -1100 mV (vs. CSE). According to the interpolation method, the parent metal has a cracking risk between -970 mV and -1050 mV (vs. CSE), with a higher risk of hydrogen embrittlement below -1050 mV. The welded joints have a cracking risk between -890 mV and -960 mV (vs. CSE), with hydrogen embrittlement risk below -960 mV. The conclusion is that the maximum negative protection potential for X80 pipeline steel should not be lower than -960 mV (vs. CSE).