Surface Crack Growth Behavior of Pipeline Steel Under Disbonded Coating at Free Corrosion Potential in Near-Neutral pH Soil Environments

EIS analysis on stress corrosion initiation of pipeline steel under disbonded coating in near-neutral pH simulated soil electrolyte

“…This is consistent with the weight-loss data reported for X65 steel (without stress applied) under simulated disbondment with the gap distance in the range of 2-20 mm [38,39]. This analysis also substantially agrees with the growth rate of SCC reported by Egbewande et al [8]. The results display that the environmental factor of SCC at the opening can be three times higher than that farther from the opening.…”

“…Corrosion and crack growth in the crack crevice were reported somehow similar with the gap between specimen surface and disbonded coating [8]. Inside crack crevice of NNpH SCC, CO2 gradient may induce electrochemical process as well as hydrogen concentration gradient that affect crack growth of pipeline steel.…”

“…The condition is general found under disbonded coating, where no significant amount of cathodic current reaches the steel, and the environment will remain near neutral pH depending upon the partial pressure of CO2. In anoxic soil conditions, dissolved CO2 is known as the most important environmental driving factor influencing anodic corrosion and NNpH SCC of pipeline steel [8,14,22]. The CO2 level in soil can be much higher as a result of microbial activities and plant root metabolism and the content shows seasonal fluctuation from 4 to 23% [7], depending on temperature, soil moisture, and amount of organic matters.…”

“…In the experiment setup follows an exponentially decreasing trend with increasing the distance from the opening. However, a weak linearly decreasing trend has been found when the gap distance was 10 mm [8]. As the gap distance becomes thinner, a sharp decrease of the corrosion rate can be expected with increasing distance from the opening.…”

“…However, corrosion and stress corrosion cracking (SCC) occur under disbonded coatings, which may prevent access of cathodic protection current to steel. SCC under disbonded coating continues to be a big issue for integrity management of high pressure pipelines [1][2][3][4][5][6][7][8].…”