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The purpose of this paper is to study the effect of cyclic hydrostatic pressure on the protective performance of cathodic protection (CP) system consisting of Zn‐Bi sacrificial anode and Ni‐Cr‐Mo‐V steel.

The anode and cathode polarization curves of the driving potential and current for CP were investigated in case of cyclic hydrostatic pressure (0‐3.5 MPa) and compared with that at atmospheric pressure. The morphologies of the anode material with and without corrosion products were observed by scanning electron microscopy.

The experimental results revealed that the cyclic hydrostatic pressure had significant influence on the CP system. The anode potential instantaneously responded to the cyclic hydrostatic pressure and the discharge performance decreased due to the deposition of corrosion product. Also, the CP system exhibited higher slope parameter under cyclic hydrostatic pressure, indicating that the CP system cannot provide adequate protection for Ni‐Cr‐Mo‐V steel.

The results presented in this paper clearly show the effect of cyclic hydrostatic pressure on the sacrificial anode CP system, and present a foundation for further research on the practical application of sacrificial anode under cyclic hydrostatic pressure environment.

To evaluate bismuth, which is inexpensive and non‐toxic, as a substitute for mercury, indium and gallium in Al‐5%Zn‐X sacrificial anode.

The effect of bismuth on the electrochemical behavior of Al‐5%Zn‐Bi in the artificial sea water environment was investigated. Potentiodynamic, potentiostatic, galvanostatic, weight loss and efficiency test methods were employed. The surface of the specimens were studied by SEM and analyzed by EDAX. Image analyzer was also used.

Adding 0.3‐0.5%Bi to Al‐5%Zn alloy produces considerable active sites on the anode surface and, when the corrosion process continues, the corrosion will be uniform by joining these numerous shallow pits and a high efficiency sacrificial anode will emerge.

Preventing segregation by good casting practice or homogenization heat treatment will be helpful to prevent unpredicted localized corrosion and investigating the effect of these processes on the performance of this new alloy is helpful. Investigating the performance of this new suggested alloy in environments like soil is highly recommended.

Owing to the toxicity of mercury and high price of gallium and indium, bismuth, which has a much lower price and showed a good performance in the present laboratory tests, can be a good substitute for the above mentioned elements.

The previous lack of a systematic research on the effect of bismuth which can be a good substitute for indium and gallium, on anodic behavior of aluminum gives this paper its high value.