The fracture of pipelines caused by corrosion cracks and the resulting oil and gas leakage can lead to great environmental pollution and economic losses. These negative effects are due to serious corrosion of the plain carbon steels used for armor of flexible pipe in oil and gas transmission medium. However, corrosion resistance of carbon steel armors has yet to be improved. In this study, the relationship between corrosion resistance and pearlite fraction in the plain carbon steels has been investigated through the application of pulsed electric current. Based on immersion test and electrochemical measurement, pulsed electric current increases the corrosion resistance of the plain carbon steels by reducing the fraction of pearlite phase. Pitting corrosion, which tends to initiate by galvanic corrosion of ferrite and cementite, is therefore inhibited due to the decrease in pearlite fraction (mixture of ferrite and cementite) under electropulsing.
Controlling the precipitation through thermomechanical treatment is an important method to improve the corrosion resistance of Al-Cu-Mg alloys. In this study, the corrosion behaviors of Al-Cu-Mg alloys in the solution-treated state and retrogressiontreated state under cold rolling deformation and then natural aging were investigated. In the solution-treated series alloys, the cold-rolled deformation improved the resistance to intergranular corrosion by suppressing the precipitation of the S-phase on the grain boundaries. The increased pitting potential and corrosion potential were related to the increased concentration of solute atoms within the grain interiors and the eliminated S-phase on grain boundaries. In the retrogression-treated series alloys, the 30% cold rolling deformation stimulated the growth of the S-phase and transformed the S-phase distribution from discontinuous to continuous on the grain boundaries, thereby changing the pitting corrosion to the network corrosion morphology. The precipitation of the S-phase with large dimension within the grain interiors contributed to the decreased pitting potential and corrosion potential.
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