Relative resistance can be described by the chloride concentration below which there is little likelihood of crevice attack occurring. The ability of chlorides to concentrate in some crevice means that occasional attack may occur at lower concentrations than shown in the following table. Crevice or pitting attack also occurs under deposits and under biofouling growths attached to the metal surface. Nevertheless, the table provides useful guidelines.
In reviewing the corrosion and biofouling properties of 90-10 and 70-30 copper-nickels in sea water, the alloys are found to possess good resistance. It is also apparent that the following requirements are necessary to achieve optimum service lives:
Obtain copper-nickel to international standards.
Use 70-30 copper-nickel consumables for similar welds in 90-10 and 70-30 copper-nickel
Use 65% nickel-copper consumables for copper-nickel to steel dissimilar welds.
Heed maximum velocity limits for the alloys.
Avoid velocity raisers e.g. sharp angled bends in pipe systems.
During commissioning do not use polluted water.
Add ferrous sulfate to enhance the protective film formation if extra caution is required.
To get the best biofouling resistance, insulate copper-nickel alloys from less noble alloys.
Releated References:
Seawater Resistance of Stainless Steel Tubes
Seawater Corrosion Resistance and Antifouling Conclusions
Copper Nickel Seawater Corrosion Resistance and Antifouling
Selection of 316 304 and 303 Types of Stainless Steel for Seawater Application
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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