[ Super Duplex ]
[ Super Duplex ]
Super duplex stainless steels in Seawater Reverse Osmosis applications
By the early 2000s , super duplexes had become the alloys of choice for highpressure seawater feed and brine reject pipework systems in seawater reverse osmosis plants . These alloys are the most commercially attractive solution for the necessary corrosion resistance in these severe application conditions .
By Dr Glenn Byrne and Mr Nicholas Hicks , Rolled Alloys , Temperance , Michigan
Seawater Reverse Osmosis ( SWRO ) projects ( circa 1980 to 1990 ) utilised various lower grades of stainless steel without success ( Table 1 ( 1 ) ). Experience in Saudi Arabia ( highlighted in yellow ) shows operators selected alloys based on the lowest cost and then gravitated to the next lowest cost option when the alloy originally selected leaked and needed to be replaced . The Malta experience ( highlighted in green ) appears to be particularly painful . It
Capacity ( m 3 / day )
Table 1 . Project experience and material performance
2,500,000
2,000,000
1,500,000
1,000,000
500,000
0
1984 1986
1988 1990
1992 1996
1998
2000
Figure 1 . The installed capacity of new SWRO plants and the alloys used ( available data for 2507 ends at 2006 and for 6 % Mo at 2015 ).
took about 10 years of trial and error before the industry accepted that 6 % Molybdenum alloys were , at that time , the only commercially available stainless grades suitable for use in high-pressure seawater feed ( HPSF ) and brine reject ( BR ) pipework systems . Having said this , some operators still insist that alloys such as 316L , 904L and 2205 have worked well .
2002
2004 2006
2008 2010
2012
ZERON 100
6 % Mo 2507
By the early 1990s super duplex stainless steels ( SDSSs ) had entered the market . Good experience in chlorinated seawater cooling , fire protection systems , and seawater pumping in offshore oil and gas applications gave SWRO contractors the confidence to use these alloys . Also , the cost differential between SDSS and 6 % Mo grades of about 30 % was attractive to the SWRO industry . By the early 2000 , SDSSs had become the material of choice for new build HPSF and BR pipe work . Contractors who continued to use 6 % Mo alloys did so because they had good previous experience with using them and didn ’ t want to change . Also , membrane and energy recovery technology improved significantly at this time , and their costs fell . This made SWRO plants readily scalable and affordable for large-scale municipal use . Consequently , there was a sudden increase in the number of new build projects , many of which used SDSS grades ( Figure 1 ). The capacity of SWRO plants being built increased by an order of magnitude , typically from 20,000m 3 / day to 200,000m 3 / day . Today , we have plants making 600,000m 3 / day of drinking water . The trend of using SDSS continues , with almost all new build and expansion projects specifying the use of SDSS for HPSF and BR pipework systems .
22 Stainless Steel World April 2024 www . stainless-steel-world . net
2015