Corrosion testing in natural waters has generally focused on assessing either resistance of materials to corrosion in a given environment or characterizing environmental corrosivity. Sometimes both can be accomplished simultaneously. For example, while the objective of another test program reported in this symposium was to determine the corrosivity of seawater world-wide, the corrosion resistance of three very diverse materials was also identified. In those tests, relatively large specimens (100 mm × 300 mm) were exposed in accordance with ASTM GS2: Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater.
This paper describes a series of corrosion tests performed to determine the general and localized corrosion behavior of two stainless alloys (UNS S31603 and UNS NO8367) and 70/30 CuNi (UNS C71500) in three aqueous environments associated with advanced reverse osmosis (RO) desalination of natural seawater. In addition to seawater (the RO feed stock), the other environments included a 2nd-pass RO brine with lower chloride content and total dissolved solids man raw seawater, and an ultrapure 3rd-pass permeate.
Two ASTM standards were reviewed for guidance in the design of the experiment Since testing could be conducted in an operating prototype RO system, the test program followed the general procedures for an in-plant corrosion tests described by ASTM G4-95: Standard Guide for Conducting Corrosion Coupon Tests in Field Applications. This standard, along with G78- 95: Standard Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Alloys in Seawater and Other Chloride-Containing Environments, provided guidance in the selection of test specimens and mounting fixtures as well as crevice formers utilized. The G78-9S standard guide also provided considerations associated wim the interpretation of the crevice corrosion test results.