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Corrosion of Alternate Marine Hull Valve Materials

Paper Number: 24
Author/s: W. C. Neil, N. Gage, C. Townsend
Organisation: Defence Science and Technology Group, Fishermans Bend 3207, VIC Australia

Abstract

The effects of long term seawater exposure on the corrosion performance of valve materials can be a significant factor in determining the suitability of a material for marine applications. Corrosion assessment by means of a long term exposure in real seawater environments is critical in determining the suitability of these materials.
This work reports on initial assessment of the corrosion of alternative hull valve material after environmental exposure in two Australian locations: Williamstown, Victoria and Innisfail, Queensland. The specimens have been exposed for 6, 12 and 36 months. Materials tested were 2205 stainless steel, Titanium (commercially pure grade 2, CP2), Inconel 625, and Nickle Aluminium Bronze (NAB) in the cast and wrought condition. Test specimens were mounted on PVC frames using nylon nuts and bolts. Corrosion assessment consisted of visual inspection, mass loss, cross sectional microscopy and testing for selective phase corrosion.
Visual inspection of the specimens indicate that the Ti, and Inconel 625 show no signs of corrosion for any length of exposure (either general or pitting) whereas the 2205 stainless steel suffered a small amount crevice corrosion. The NAB specimens show signs of general corrosion and pitting for all exposure periods.