Correlation efficiency of sacrificial anode Al-Zn-In toward movement of polarization curve using potentiodynamic method

The development of oil and gas exploration in deep water area with the depth of more than 1000 feet (300 m) requires more efficient and reliable protection design to preserve high cost offshore building structure. Cathodic protection system of Aluminum sacrificial anode is assumed to be sufficient to protect offshore structure in deep water area. One of the important parameters in assuring working quality of Al anode is the efficiency of its anode, performance of anode to contribute the maximum protection current in order to protect the structure. This study focusing on the test of efficiency sacrificial anode Al-Zn-In refers to standard of NACE TMO 190-98 Item No. 21221 concerning Impressed Current Laboratory Testing of Aluminum Alloy Anodes, especially Hydrogen Evolution Method, and its result will be associated with the electrochemical test using potentiodynamic method. The aim of this study is to determine the relation between efficiency with polarization curve, corrosion potential of anodes, and mixing potential to predict the protection potential of steel in sea water. Investigated anode samples which have various alloy composition represent efficiency of anode ranging approximately from 60% to 90%. The result of this study indicates that efficiency of anode has opposite comparison with collected hydrogen volume. Anode which has highest efficiency, 94.2%, only has the average of collected hydrogen volume of 16.1 mL, while anode that has lowest efficiency, 63.8%, has the average of collected hydrogen volume of 148.4 mL. Furthermore, efficiency has significant influence in the movement of polarization curve, corrosion potential of anode, and mixed potential of protected steel in synthetic seawater. The mixed potential obtained from superimposed of cathodic polarization curve of steel and anodic polarization curve of anode can be used to predict the maximum protection potential of steel that using Al-Zn-In sacrificial anode. If a protection potential of steel can be examined, then the corrosion rate that structure can also be determined using the intersection of steel anodic extrapolated curve at the protection potential. The aluminum anode which has efficiency 94.2% can give a maximum protection potential of the structure - 0.952 Volt vs SCE, while the anode which has efficiency 63.8% can give a maximum potential -0.866 Volt vs SCE. Although the actual protection potential of protected steel would be more positive than the mixed potential due to ohmic voltage drop, it could be employed as a prediction for designing cathodic protection system using sacrificial anode.