해수중 음극방식용 희생양극 성능 시험법의 비교 연구

Abstract

Cathodic protection(CP) with coating is well established and applied to mitigate the corrosion of ships, ocean structures and many other facilities. The CP is subdivided into two techniques, i.e., impressed current CP(ICCP) and sacrificial anode CP(SACP). In the case of large on- and off-shore structures, the later is preferential since it is hard to obtain the power sources for protection in remote marine circumstances. In the SACP, normally zinc and aluminum anodes are used in the form of alloy mixed with so-called, activation elements both to prevent passivation on anode surface and to enhance efficiency of its performance. Especially the aluminum anodes are remarkably influenced by the activation elements, like zinc and indium, as well as the manufacturing process of alloying.

Consequently, performance (efficiency) test of anode is very important for a long-term protection of structures in seawater which is known as the most corrosive environment in natural condition. Many countries have their own standard for testing sacrificial anodes, and some standards are well recognized internationally. However, the test results between those standards are not well agreed. There are few studies regarding the comparison of sacrificial anode test methods.

In this study three standards, i.e. KS(Korea), NACE(US) and DNV(Norway), have been selected to compare the performance of zinc and aluminum anodes, and short-term laboratory performance experiments have been conducted. Some electrochemical characteristics have been investigated and anode efficiencies have been compared.

The results of these performance tests were as follows

1. The performance test results of sacrificial anodes among

three standards were significantly different.

2. In all three standard tests, the efficiency for Al anode was

much lower than that for Zn, which is assumed due to the

passivation of Al anode surface.

3. The order of anode efficiency for three standards was

NACE(mass) > KS > DNV > NACE(H2) for Zn anode, and

DNV > KS > NACE(mass) > NACE(H2) for Al.

4. The possible reasons for the discrepancy/error between

the standards may include not only the test period & the

applied current density in regulations, but also the

coulometer treatment and the removal of corrosion

products from anode surface after experiment.