Effect of alternating current on the corrosion of K60, K70, and K80 pipe steels in seawater

The effect of alternating current (AC) on the corrosion of K60, K70, and K80 pipe steels (approximately corresponding to API 5L X70, X80, and X90 steels) in synthetic seawater was studied at the free corrosion potential and at cathodic potentials corresponding to various modes of electrochemical protection (ECP) of pipelines.It has been shown that at the corrosion potential, AC (100 A/m 2 ) accelerates corrosion of the studied steels severalfold, reaching 1.1-0.7 mm/year.If the potential is shifted in the negative direction, the corrosion rates of steels decrease both in the absence of and under the action of alternating current.At ECP potentials (from -0.65 to -0.9 V vs. SHE) and an AC density of 20 A/m 2 , the corrosion rates of steels are less than 0.1 mm/year.With an increase in alternating current density to 100 A/m 2 and at potentials of -0.7 and -0.9 V, the corrosion behavior of steels differs.The corrosion rate of K70 steel is less than 0.1 mm/year and decreases with polarization time, while the corrosion rates of K60 and K80 steels increase with polarization time to approximately 0.2 mm/year.