RECOMMENDED PRACTICE CATHODIC PROTECTION DESIGN OCTOBER 2010

TEST Engineering & Management, 2019

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.

The cost of corrosion in the U.S. in 1986 was estimated to be close to $180 billion. Furthermore, estimates show that $70 billion worth of corrosion loss could have been prevented in 1986 by applying modern corrosion control technology. This section discusses the corrosion of metal in contact with moist soil or water, and the tendency of some metals to corrode preferentially with respect to other metals when located in the same environmental conditions. The use of a superimposed current to prevent or reduce the rate of corrosion by making the entire metal surface the cathode of an electrochemical cell and providing a separate anode is called cathodic protection. This section discusses the mechanisms of cathodic protection and the types of cathodic protection systems available for corrosion control. The different types of cathodic interferences are covered along with the safety considerations. A glossary of cathodic protection terms is also included. Sections 1200-1600 discuss specific applications of cathodic protection systems. The best cathodic protection system in the world is of no value if not properly checked and maintained. See Section 1800 on maintenance for details. Contents

Brodogradnja

Corrosion is the gradual deterioration of a material or its properties through a chemical reaction with its environment. There are several methods of preventing a material from corroding. Cathodic protection (CP) and coatings are very popular methods for corrosion protection. Each individual method has its own benefits and drawbacks, whereas experience has shown that the most effective method of corrosion prevention is a combination of both CP and coatings. This combination can provide very good protection over a long period of time. This paper focuses on the combined use of both CP and coatings for ships. Calculation of a CP design is explained briefly and the factors affecting the choice of the type of CP system are demonstrated. Then, a sample anode plan of a ship is shown. Finally, the calculation of a cathodic protection system of a ship is presented using data provided by coating manufacturers and shipyards.