Application of stainless steel in seawater desalination
Nickel-containing duplex stainless steel, super duplex stainless steel, and super austenitic stainless steel have become popular materials in the field of seawater desalination due to their excellent corrosion resistance and high strength. At present, S31603 and S31703 stainless steel and copper-nickel alloys (at least used in lower temperature and chloride environments) mainly used in the desalination industry cannot ensure the required long-term reliability. Although the unit cost of high-nickel stainless steel is relatively high, due to its high strength, the thickness of the material can be reduced during use, thereby reducing weight and cost, and is quite competitive with the currently used materials. With the extension of the design life of newly built large facilities (the average design life is now more than 40 years), life cycle costs have become more important.
In 2004, Outokumpu (formerly Avista) published two pieces of information about nickel alloys used in desalination plants. For multi-stage flash evaporation (MSF) equipment, the selection of materials is recommended as follows:
◆ Condenser tube (usually titanium or copper-nickel alloy) uses S31254, S3275O and S32654;
◆ $32654 for brine heater tube and tube sheet; spring
◆ The shell of the flash chamber uses $32205 (exempt painting and reduce maintenance) and S31254, $32654 (sealing surface, flange connection);
◆ “Downstream sections” use $32205.
◆ For reverse osmosis (RO) equipment, the selection of materials is recommended as follows:
◆ S31254 for high-pressure pump, $32750 (for high chloride environment) and IS32205 (for low chloride environment);
◆ $32750 for high pressure pipeline.
Due to the high strength of the $32205 duplex stainless steel spring, the evaporator container can be made thinner and lighter, which is 30% lighter and thinner than the S31603 equipment. For a multi-stage flash swallow plant with a production capacity of 16,000 cubic meters per day in Libya, $32205 pairs The price of stainless steel equipment is more competitive. This is the first commercial application of $32,205 in evaporator containers since the 1993 Yokohama Conference in Japan. At that meeting, it was first proposed to use integral duplex stainless steel for the evaporator vessel.
At the International Conference on Desalination and Water Reuse of the International Society for Desalination Chemistry in 2005, Outokumpu announced the use of economical duplex stainless steel for the Taweelah B expansion project and the IJebel Alil project. The bottom of the evaporator of these factories will be exposed to dry degassed seawater, and $32205 duplex stainless steel will be used; the upper part of the evaporator will be exposed to dry and corrosive condensate, and the $32101 nickel-type duplex stainless steel will be used. The super austenitic alloy N08367 with 24% nickel, 20% chromium and 6% molybdenum has been widely used in seawater treatment facilities. At the 2003 National Association of Corrosion Engineers (NACE) International Conference, researchers published a paper, discussing the application of N08367 in reverse osmosis process and multi-stage flash process seawater desalination unit. N08367, as a competitive alternative material, is used to replace traditional copper alloys. Copper alloys have some advantages, such as high thermal conductivity, but copper alloys are also subject to erosion caused by liquid flow, especially in the presence of contaminants such as sulfides and amines. Although the price of N08367 alloy is higher than that of copper-nickel alloy, it is still competitive. This is because the equipment using this alloy can be thinner, lighter in weight, and therefore cheaper. In recent years, this alloy has been designated for use in many factories, including the key pretreatment pipeline of the reverse osmosis unit constructed in Trinidad, Western Hemisphere in 2002, with a design capacity of 109,000 cubic meters per day. In 2001, an article introduced the use of thin-walled laser welding $34565 austenitic stainless steel pipes in the evaporation chamber of the heat recovery section of the multi-stage flash evaporation process device as an economical alternative material for 90/10 copper-nickel alloy. $34565 austenitic stainless steel usually contains 17% nickel, 24% chromium and 4% molybdenum. In addition, it is reported that my country’s Henan Dechang Copper-Aluminum Profile Co., Ltd. has been commissioned by Israel’s IDE company to independently research and develop seawater corrosion-resistant special aluminum alloy tubing. This product is mainly used for direct use of seawater, seawater desalination, marine chemicals, Ships and other projects. The successfully developed seawater corrosion-resistant special aluminum alloy tube has the following properties: (1) non-toxic side effects • (2) seawater corrosion resistance • (3) stable mechanical properties and corrosion resistance in seawater media below 120 degrees. (4) Good thermal conductivity (5) Can withstand pressures above 1.5MPa (6) Good workability (7) Low price.