Polarization Resistance Measurements of Copper Nickel Alloys in Seawater

摘要

As a result of problems associated with the brazing of seawater piping systems on Canadian Forces surface ships, it has been proposed that future ships have welded systems. This proposal has necessitated the investigation of the properties and behavior of potential replacement weldable alloys for the nonweldable cast ASTM B61 leaded tin bronze presently used for fittings. In a previous investigation, cast chromium modified 70/30 copper nickel exhibited erosion corrosion resistance, under severe conditions, equal to or better than that of the presently employed seawater piping system materials. In order to further understand this alloy's erosion corrosion behavior, its corrosion rate was measured in static seawater using the electrochemical polarization resistance technique. For comparison purposes, the corrosion rates of the present seawater piping system materials, wrought 90/10 copper nickel and cast leaded tin bronze (ASTM B61), and another potential replacement weldable alloy, cast niobium modified 70/30 copper nickel, were also measured. The polarization resistance evaluation indicated that the cast chromium modified 70/30 copper nickel alloy had a similar level of resistance to corrosion in static seawater as the presently employed materials. Its corrosion resistance, however, did not consistently decrease with increasing temperature, as it did under severe erosive conditions.