Development and Application of NSSC2120 Stainless Steel Used in Seawater Desalination Unit
As a measure to solve the problem of global water resources, the demand for seawater desalination equipment is increasing. However, to control the construction cost of seawater desalination equipment and increase the production capacity of seawater desalination equipment, large-scale evaporative seawater desalination with a large amount of water production function The device uses various corrosion-resistant materials.
The main corrosion-resistant material used is duplex stainless steel. To expand the user’s choice of corrosion-resistant materials and be able to choose more reasonable corrosion-resistant materials, Nippon Steel & Sumikin Stainless Steel Co., Ltd. has developed low-alloy dual-phase steel with good weldability, namely NSSC2120. This article introduces the characteristics and applications of the newly developed stainless steel-NSSC2120 for desalination equipment.
Super Duplex 2507 Stainless Steel Welded Tubes
1. Stainless Steel for Seawater Desalination Device
The metal materials used in the multi-stage flash seawater desalination device that can efficiently desalinate sea water in large quantities are shown in Table 1. According to the changing salt concentration and temperature conditions of the seawater desalination process, stainless steels with different corrosion resistance are combined and used. For austenitic stainless steel, 316L with high pitting resistance is used, and duplex stainless steel is used for parts with high salt concentration and severe corrosive environment.
The characteristic of duplex stainless steel is that, from the perspective of metal composition, its resistance to stress corrosion cracking caused by chloride ions is stronger than that of austenitic stainless steel, but its corrosion resistance depends on the addition of effective corrosion-resistant alloys such as Ni and Mo. But different. Compared with the duplex stainless steel standard ASTMS31803 (22%Cr-5%Ni-3%Mo), the steel grades such as S32101 (21%Cr-1.5%Ni-N) with fewer alloying elements are called low-alloy duplex steels.
2. Development and Characteristics of NSSC2120
The advent of low-alloy dual-phase steels with as little as possible the addition of precious metals such as Ni and Mo has further expanded the application range of duplex stainless steels. Low-alloy dual-phase steel has three advantages: ①The corrosion resistance is the same as that of ordinary austenitic stainless steel used in a moderate salt environment; ②The alloy cost is low, and the price change is small; ③The yield strength is about the same as the austenitic system It is twice the steel grade, so low-alloy dual-phase steel can be used as economical dual-phase steel to expand its application to replace ordinary austenitic stainless steel.
However, the low-alloy dual-phase steel represented by S32101 in the past has the problem of deterioration of corrosion resistance and toughness during high heat input welding, and it is difficult to apply submerged arc welding to high-efficiency welding of structural parts. The main chemical composition of NSSC2120 is 21%Cr-2%Ni-N. By balancing the distribution ratio, the welding problem is solved, and it can be applied to high-heat input welding.
From the comparison of the corrosion resistance of NSSC2120 stainless steel, other duplex steels, and austenitic steels in the artificial seawater CCT test, it can be seen that NSSC2120 has the same pitting corrosion resistance as TY304. In addition, in terms of stress corrosion cracking resistance, due to the mixed structure and high strength of dual-phase steel, its stress corrosion cracking resistance is better than TY304.
3. Application in a Seawater Desalination unit
According to the characteristics of NSSC2120 stainless steel, its characteristics as a material for seawater desalination equipment have been evaluated, and the result is that it can be used in Qatar’s largest seawater desalination equipment. The seawater desalination unit uses a total of 3200t duplex stainless steel, of which 700t is NSSC2120. Because it can greatly improve the welding operability, it can replace S32101. In the future, NSSC2120 can be expanded to be used in large-scale desalination plants in the Middle East.
4. Application in Other Industries
NSSC2120 has begun to be widely used in other industries. The Japanese shipbuilding industry has extensively used NSSC2120 when manufacturing offshore tankers instead of TY304 and coated carbon steel plates, which not only ensures corrosion resistance, but also has good workability and weldability, and can also simplify maintenance during navigation.
In the future, NSSC2120 can be applied to ocean-going tankers. In addition, NSSC2120 can also be used in reservoir gates and water treatment equipment. Affected by the Great East Japan Earthquake and Tsunami, the infrastructure along the northeastern coast of Japan was severely damaged, and there are many gates and water treatment equipment that require mid-to-long-term maintenance and reconstruction.
Nippon Steel & Sumikin Stainless Steel Co., Ltd. has applied for technical registration of high-strength low-alloy dual-phase steel to the New Technology Information Agency of the Ministry of Land, Infrastructure, Transport, and Tourism to accelerate its application in the construction of public infrastructure projects such as gates, reservoirs and dike facilities that adopt new technologies.
5. In Conclusion
Because NSSC2120 has the same corrosion resistance and high strength advantages as TY304 in a low-carbon environment, it is estimated that it can be used not only in energy equipment but also in other industries in the future. In the construction industry, NSSC2120 has the advantages of being lightweight and maintenance-free, so it can replace the previous structural parts and accessories using galvanized steel.
Since the elastoplastic properties corresponding to tensile stress are closer to carbon steel than ordinary austenite, it can be used as a structural component in the future. Recently, NSSC2120 stainless steel has been used to replace galvanized steel sheets in steel for large-scale solar stents. In addition to its maintenance-free features, NSSC2120 also has the advantages of lightweight and cost reduction, which is the biggest reason for its adoption.
With the continuous expansion of the application range of NSSC2120 stainless steel, the products have expanded from the original thick plate products to a thin plate and rod wire products. In addition, in terms of component production, in cooperation with related companies, we have prepared a variety of secondary processing products such as welded pipes, joints, section steels, castings, and forgings to meet the various needs of users.