Justification and Judgement to Corrosion Issues for Anode Selections on Navy ships

Abstract

Sacrificial anodes have become an utmost technique to protect the exterior hull, stern drives and outboard parts of the ship. For many decades, zinc anode has become commonly used in cathodic protection devices as sacrificial anodes since it has been the easiest and cheapest material to be used and has done a decent job in most natural applications of seawater. Due to its elevated theoretical present effectiveness and low active potential, aluminium appeared as an exciting metal to replace zinc in the cathodic protection scheme. In this research, the performance of zinc alloy and aluminium alloy (will be mentioned as Al and Zn) as an anode to cathodic protection was assessed at distinct temperatures (20°C and 40°C) on the marine structure plate or ship's hull which made by carbon steel in natural seawater. Wavelength dispersion X-ray fluorescence spectrometry (WDXRF) has been used to evaluate the composition of the Al and structure plate (carbon steel) whereas atomic absorption spectrometer (AAS) and X-ray diffraction spectrometer (XRD) were used to assess the composition of a Zn and natural seawater. The magnitude of corrosion protection was determined by weight loss (immersion testing) and electrochemical by cyclic polarisation potential (CPP) technique. It has been observed that the weight loss of Zn is higher than Al after 4 weeks immersed in natural seawater at 20°C and 40°C. Similarly, the electrochemical data by CPP showing Al to have better corrosion resistance than Zn alloy due to instant oxidation and resistance to dealloying process. Overall results show that Al alloy has better performance than Zn alloy as sacrificial anode for cathodic protection in seawater. The potential of Al alloy is higher than Zn alloy on marine structure plate (carbon steel) in natural seawater, thereby becoming preferable protective cathode. Both anode materials show to have potential between -800mV to -900mV showing best galvanic potential over steel plate to be protected.