Non-isothermal effects induced by natural illumination and infrared irradiation on cathodically polarized carbon steel electrodes

• Visible and IR power (650 W/m2) enhance oxygen limiting current in NaCl solution.
• Simulations and experiments show that impinging power is dissipated by convection.
• The convective nature of the irradiation depolarization effect is verified.
• Sunlight is expected to not affect cathodic protection requirement in real seawater.

Experimental–theoretical approach was developed to analyse the heating behavior of carbon steel electrodes cathodically protected in quiescent NaCl 3.5 wt.% solution and exposed to irradiation. Natural and infrared wavelengths induced an increase of electrode surface temperature, enabling to determine oxygen limiting current enhancement. Numerical simulations of laboratory tests performed with infrared wavelength indicated that the Nusselt number ranges between 3.5 and 6, revealing the convective nature of the irradiation depolarization effect. The results obtained in NaCl 3.5 wt.% solution permit us to state that in seawater environment the sunlight depolarizing effect does not affect the current demand for cathodic protection.