Materials Performance

NOV 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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13 NACE INTERNATIONAL: VOL. 53, NO. 11 MATERIALS PERFORMANCE NOVEMBER 2014 Corrosion of Type 316 stainless steel in deaerated seawater Q: We are comparing Ty pe 316 stainless steel (SS) (UNS S31600) and duplex SS for their suitability in deaerated (5 to 7 ppb of O 2 ) seawater at 105 °F (41 °C). We assume the corrosion rate of Ty pe 316 SS will be marginal at that temperature and O 2 level. We have a reverse osmosis (RO) plant downstream of the deaerator. To avoid fouling of the membranes, the vendor is suggesting using duplex SS for the piping. We feel that since the water is deaerated, we can use Ty pe 316 SS as a cheaper option. Hence, we want to compare the corrosion rates of Ty pe 316 SS and duplex SS in this service. A: We had a seawater RO plant ofshore of California. Te sea water intake was a submerged concrete structure ofshore. Te water was then gravitated to a concrete forebay structure located right on the beach via a 90/10 Cu/Ni line. Te seawater was then pumped to the RO plant located on a hill. Te line from the forebay to the RO plant was 70/30 Cu/Ni. Te piping at the inlet of the RO plant was chlorinated poly vinyl chloride (CPVC) and fberglass-reinforced plastic (FR P). Te seawater was passed through a roughing multi-grade rapid sand flter followed by a polishing multi- grade flter. Te fltered seawater was then processed with an ultraviolet steril- izer followed by a 5-µm cartridge flter. At this point, the operating pressure was 60 to 90 psi (0.4 to 0.6 MPa). A ll piping was either Cu/Ni, CPVC, or FR P at this point. Te water was then sent to the suction of the plunger pumps. Te discharge piping was SMO-254. Te discharge pressure was 1,000 psi (6.9 MPa). Te discharge piping on the permeate side was Ty pe 316 SS. Te brine reject piping was SMO-254. In 17 years of service, there have been no corro- sion failures in this system. Editor's Note: Additional MP Blog items appear in the individual technical sections: cathodic & anodic protection (p. 38), coatings & linings (p. 43), chemical treatment (p. 56), and materials selection & design (p. 68). More than 3,000 corrosion professionals from all over the world participate on the NACE International Corrosion Network and NACE Coatings Network. You can post your question and receive expert advice in a matter of minutes. To join either or both of these free list servers, go to the NACE Web site: www.nace.org, click on the "Corrosion Central" link, and then "Online Corrosion Community List Servers." The networks look forward to your participation!

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