CORROSION OF METALS IN TROPICAL ENVIRONMENTS. PART 8. NICKEL AND NICKEL-COPPER ALLOYS: SIXTEEN YEARS' EXPOSURE
NAVAL RESEARCH LAB WASHINGTON DC
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Corrosion of nickel and nickel-copper alloys in five natural tropical environments is reported for exposure periods of 1, 2, 4, 8, and 16 years. Data collected include weight loss, pitting, change in tensile strength of simple plates, and weight loss of galvanic couples. Corrosion in the tropics is compared with available exposure results from temperate latitudes in the United States, and generally the tropical corrosion was appreciably higher. The weight-loss-vs-time curves are normally curvilinear relations but considerable variation in the direction and magnitude of the curvature was observed for the different metals and environments. With respect to pitting, the high nickel alloys developed severe early pitting under sea water. Comparison under tropical sea water of monel and copper-nickel with various other nonferrous metals shows copper-nickel with comparatively high corrosion resistance, but monel with the lowest sea-water resistance of the group. Galvanic corrosion results show the long-term efficiency of carbon steel anodes in cathodically protecting nickel-copper alloys in sea water. Additional galvanic data reveal that considerable anodic corrosion can be induced in a normally sea-resistant metal if coupled with certain nickel alloys. The nickel metals were highly resistant to corrosion in the tropical atmospheres. There was no measurable pitting in these terrestrial exposures and only small weight losses. The losses that were measured though showed increasing resistance of the metals with increasing nickel content.
- Properties of Metals and Alloys