General Corrosion Rates
Once a good surface film forms, the corrosion rate will continue to decrease over a period of years and to exhibit the classical parabolic growth rate of protective layers. For this reason, it has always been difficult to predict the life of copper-nickel based alloys based on short-term exposures. Normally, corrosion rates of 0.02-0.002 mm/yr are anticipated.
Specific corrosion rate measurements at LaQue Corrosion Services taken over fourteen years in tidal, flowing (0.6m/s) and quiet seawater show the corrosion rate decreases over a period of 5-6 years, stabilising out at about 1.3µm/yr, as shown in Figure 2.
The presence of sulfides in polluted water and the decomposition of organic matter may lead to higher corrosion rates and pitting, as will be discussed later.
Copper Nickel for Seawater Corrosion Resistance and Antifoulin
90-10 and 70-30 Copper-Nickel Alloys
Corrosion Resistance
The Importance of the Surface
General Corrosion Rates
Localised Corrosion
Velocity Effects
Sand Erosion
Galvanic Properties
Handling Sulfides
Ferrous sulfate treatment
Biofouling Resistance
Ease of Biofouling Removal
Reasons for Biofouling Resistance
Boat Hull Experience
Offshore Sheathing
Conclusions
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