Materials performance in SWRO desalination plant at KISR research and development program

During the past 15 years of R&D program in seawater desalination at KISR, many metals and alloys have been studied for their corrosion behavior. Stainless steels, nickel-base alloys, titanium among the groups of alloys that were evaluated. Linear polarization, cyclic polarization, open-circuit potential, impedance spectroscopy, crevice corrosion and erosion corrosion were some of the major techniques and tests used to evaluate the candidate materials for this program. Tests indicated that austenitic stainless steel UNS S31603 and UNS S31703 were the least favored to be used in the construction of seawater reverse osmosis units.

The following main findings resulted from these various studies: 1. Metallic components used in the construction of RO an plant can greatly affects plant’s performance. 2. Electrochemical studies give an indication of the relative resistance to pit initiation, propagation, and repassivation behavior. Good correlation was obtained between the electrochemical results and weight loss results. 3. The significant beneficial effect of increased Cr, Mo, Ni, and N contents on the corrosion resistance of alloys in high salinity seawater and concentrated brine were demonstrated. 4. The poor performance of S31603 and S31703 in electrochemical tests is attributed to the nucleation and repassivation of pits on the surfaces of the alloys. 5. The incidence and intensity of crevice attack on S31603 and S31703 were the severest during the study. 6. S31726, S31254, S32550, N05500, N08904, N06625, N08367, N10276 are good alternatives for the construction of RO units, however, the initial cost is higher.