Abstract
Hydrostatic pressure effects on pitting initiation and propagation in X70 steel are investigated by evaluating metastable pitting probability using electrochemical methods and immersion corrosion tests in containing chlorine ion solution. Potentiodynamic tests indicated that hydrostatic pressure can decrease the breakdown potential and lead to a reduced transpassivity region. Metastable test results revealed that hydrostatic pressure can increase metastable pitting formation frequency and promote stabilization of metastable pitting growth. Electrochemical impedance spectroscopy (EIS) results indicate that Hydrostatic pressure decreases the charge transfer resistance and increases the dissolution rate within the cavities. Corrosion test results also indicated that pitting initiation and propagation are accelerated by hydrostatic pressure. Result validity was verified by evaluating metastable pitting to predict pitting corrosion resistance.
Highlights
There are significant amounts of resources in the deep ocean, including oil, gas and valuable minerals
Alloy pitting corrosion resistance increases with Epit, this means that the X70 pipeline steel corrosion resistance is worsened by hydrostatic pressure
The hydrostatic pressure effects on pitting initiation, metastable pitting and propagation in X70 steel have been investigated by evaluating metastable pitting events and immersion tests
Summary
There are significant amounts of resources in the deep ocean, including oil, gas and valuable minerals. It is necessary to evaluate pitting susceptibility of the X70 pipeline steel in the deep sea environment. Beccaria et al [4,5,6,7,8] studied the effects of hydrostatic pressure on corrosion behavior of passive metals using a pressure vessel. While previous studies focused on passive metals, there are only a few fundamental reports of the hydrostatic pressure effects on pitting of active metals. Hydrostatic pressure effects on pitting corrosion initiation and propagation of X70 pipeline steel were studied by evaluating metastable pitting events using electrochemical methods in 0.5 mol/L NaHCO3 + 0.1 mol/L NaCl solution. To verify the potentiostatic method accuracy, immersion corrosion experiments were performed in 0.1 mol/L NaCl solution
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