Cathodic protection ICCP anodes

Cathodic protection is probably the most important of all approaches to corrosion control. Using an externally applied electric current, corrosion is reduced essentially to zero. A metal surface that is cathodically protected can be maintained in a corrosive environment without deterioration for an indefinite time. There are two types of cathodic protection impressed current cathodic protection (ICCP) and sacrificial anode cathodic protection (SACP), also known as galvanic cathodic protection. 

When an impressed current cathodic protection (ICCP) system is in full operation there is a high possibility for oxygen to be produced at the anode, and in nearly all cells, hydrogen is formed at the cathode. If chloride ions are present, chlorine gas may be formed at the anode. This generation of gas, either oxygen or chlorine, at the anode is not nearly as likely to occur in a natural corroding cell as it is when an ICCP system is used, particularly when inert anodes are used. 

Impressed current cathodic protection (ICCP) and sacrificial anode cathodic protection (SACP) systems were designed... 

It was found, for example, that a protection current density of 30 mA/m in quiet seawater rises to over 110 mA/ m at 15 knots and above. Ship ICCP anodes are few in number and very small in relation to the cathodic surface area, thus the distribution of potential from them is inevitably uneven. In the design process, it is the difficulty of knowing the expected potential distribution over the structure that leads to reliance on current density measurements as a means of assessment. Yet many ship ICCP designs utilize no more than two or three reference electrodes and these electrodes can only measure the potential in their adjacent vicinity. 

With the ICCP system shown in Fig. 13.10, the groundbed anodes are not really providing the driving power. Instead, some external source of direct electric current is connected (or impressed) between the structure to be protected and the groundbed anodes. The positive terminal of the power source is connected to the groundbed, which is then forced to discharge as much CP current as is desirable. If a mistake is made and the positive terminal is connected erroneously to the structure to be protected, the structure will become an anode instead of a cathode and will corrode actively. 

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