Desalination plants are known to be very corrosive because of the high temperatures in the environment. Austenitic stainless steels of the previous 300 series are often the preferred materials for desalination plants. In cases where higher corrosion resistance is required, typical material solutions have exceeded the higher alloyed austenite grades of the 300 series stainless steels such as austenitic 6Mo grade (UNS NO 8367)ii.
Recently, in many cases, 2205 stainless steel and other duplex stainless steels have become more optimized materials. There are many reasons why 2205 stainless steel and other duplex stainless steel have gained popularity in the seawater desalination industry. First, duplex stainless steels have good corrosion resistance and in many cases can save costs compared to comparable austenitic stainless steels. For example, Duplex 2205 has similar pitting and crevice corrosion properties as 904L (UNS No 8904) but can be obtained at a lower cost because its chemical composition includes a lower percentage of expensive metal ii. In addition, duplex stainless steel has high strength. Specifically, 2205 is almost twice as strong as austenitic stainless steel. Therefore, less material weight is usually needed, which can further save costs.
Duplex stainless steels have been successfully implemented in many applications in desalination plants, including evaporators, as well as SWRO BWRO high pressure piping, and numerous parts and product water processing connections II. Here are some specific examples.
Solid Duplex and Duplex Evaporators:
The breakthrough in dilute industrial duplexing occurred in 2003 when the 2205 was selected for installation at the MSF plant in Melittah, Libya, Italy, built by Italy’s REGGIANE. The 2205 can use thinner plates to build evaporators than conventional evaporator materials such as austenitic 316L (UNS S31603), requiring less material and less welding. Other advantages include easier handling and lessening the overall impact of the environment on me. Both the Melittah factory in Libya and the Skikda factory in Algeria (built in 2004 and 2005) have successfully demonstrated the ability of Duplex 2205 to meet the needs of these environments.
With the successful application of the 2205 evaporator, Outokumpu proposed the DualDuplexx evaporator concept. The DualDuplex evaporator uses two different types of duplex stainless steel in the evaporator structure to maximize cost and material savings. 2205 For parts exposed to the most severe conditions and thin duplex, LDX21011 (UNS 32101) and Duplex 2304 (UNS 32304) are used for parts exposed to less harsh conditions [iii]. The high strength of the lean duplex makes it possible to increase the gauge of these components by up to 50% compared to austenitic stainless steels, although the limits in design specifications limit the actual savings by about 35% to 40%. DualDuplexx evaporators have been successfully implemented in several desalination plants, including the Taweelah B expansion in Abu Dhabi, the Jebel Ali L plant in Dubai and the Ras Abu Fontas desalination plant in Qatar.
SWRO high pressure pipe:
The experience of the large number of seawater reverse osmosis (SWRO) plants already in use shows that if the wrong stainless steel is used in the high-pressure piping required for this environment, there is a high risk of corrosion. The 316L (UNS S31600) and 317L (UNS 31603) grades do not have sufficient corrosion resistance to withstand this environment. Therefore, highly alloyed austenitic steels, such as 254 SMO (UNS S31254), are considered to be more or less mandatory years v. However, recently, the super-duplex brand such as the SAF 2507 (UNS S32750) has made great progress in this area. The SAF 2507 is an ideal solution, with almost the same resistance as pitting and crevice corrosion of 254 SMO, twice the strength, and much lower cost than v. Singapore’s Singspring desalination plant provides about 10% of fresh freshwater demand and is a good example of SAF 2507s’ successful implementation. SAF 2507 is used for the high pressure pipeline iv fed to the incoming seawater through initial seawater reverse osmosis (SWRO). Singspring has been running since 2005 and SAF 2507 continues to perform well.
Source: China Duplex Stainless Steel Pipes Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)