The advantage of duplex stainless steel is its excellent corrosion resistance, especially local corrosion resistance. In addition, its strength is equivalent to two times of austenitic stainless steel, toughness is also very good, not only for the traditional paper-making and chemical processing industry equipment, but also used in important public engineering fields, such as bridges and highway construction. This paper introduces the development trend of duplex stainless steel from two aspects of materials and applications.
Economical duplex stainless steel
There are three kinds of mature duplex stainless steel developed abroad. One of them is UNSS32001. It is a new type of steel which is difficult to produce delta phase. It has been used in deep sea pipeline cable and automobile frame. The second grade is UNSS32101, which can be used in medium corrosive environment, such as the white tank of paper mills, etc., and its potential use is very wide. In recent years, the steel has been paid special attention to the basic structure, and has been successfully used in the construction of bridges. These two grades of steel are manganese and nitrogen instead of nickel, reducing nickel and chromium content, their corrosion resistance and 304LH equivalent, because it does not contain molybdenum, it is cheap, but not suitable for coastal structures. The third grade is UNSS32003, whose internal nickel content is 3.5%, higher than the first two kinds of stainless steel, and also contains 1.7% molybdenum, can be used in the depth of 1200m submarine transport of sulfur free or slightly sour gas pipeline system.
Super duplex stainless steel and duplex stainless steel
SAF2507 steel developed in Sweden is the use of the most widely used steel super duplex stainless steel, has been incorporated into the multi criteria, the microstructure of the balance between the good, is more likely to be in the hands of similar stainless steel in the production process, especially has very excellent in high chloride environment localized corrosion resistance, making the heat exchanger of sea oil pipeline cable, seawater desalination, flue gas desulfurization device used frequently. The Zeron100 steel containing W and Cu has been developed in the UK. The steel has been successfully used in seawater jet pumps and lift pumps because of its good wear and corrosion resistance.
From a technical point of view, the sea is the most valuable use of the industrial field of super duplex stainless steel, but is in order to adapt to the current wellhead improvement of oil and gas recovery method control system for higher corrosion resistance requirements and deep seabed temporary piping and piping cable demand, existing duplex stainless steel in strength and corrosion resistance has been insufficient, the Swedish Sandvik company designed a new series of super duplex stainless steel SAF2906, SAF2707HD, SAF3207HD etc. with strength up to 1000MPa ultra high strength and excellent corrosion resistance of steel.
In addition, the Alloys developed by Langley controls the corrosion resistance and pitting corrosion resistance of the Ferralium 225-SD50 steel, which is higher than that of other super duplex stainless steel.
Popularization and expansion of application
The application of duplex stainless steel is more and more extensive. Traditionally, its excellent local corrosion resistance, especially the stress corrosion resistance, is considered as a corrosion resistant functional material. Now, from its strength, the application of duplex stainless steel as a modern structural material should be paid attention to.
Because of the increased demand for oil and gas, driving deeper and deeper undersea oilfields, this has rapidly increased the use of deepwater wells. The main oil production platform implements the operation of standardized pipe bundles to provide water, power, decompression and communication over wells. In addition, in order to ensure the mobility of oil, chemical injection is required in many deep sea intake pipes. In order to increase production, the oil well is acidified by pipeline cable. The pipeline cable has become the lifeline of the seabed mining system. Faced with deep-sea exposure environment, it means that high mechanical properties, internal and external corrosion resistance, stress corrosion cracking and other requirements for pipeline cable are required. The preferred material of deepwater pipeline cable should be super and super duplex stainless steel, but because of the price and manufacturing problems, the galvanized 19D duplex stainless steel (ZCLDSS) has been developed. The design life of the pipeline cable is 20 years, and it has been popularized and applied at present. In addition, the economical low nickel AL 2003 steel has also been used in the East Malaysia oil field in 2006, the depth of more than 1200m submarine pipeline. Adding copper Ferralium225-SD50 duplex stainless steel has become a container material 7000m deep seabed placing equipment and cables, and the pressure on the shell were used as underwater locator and extremely accurate controllable deep-sea acoustic release transponder and bearing components (7000m deep sea is equivalent to 700 ATM, HI2.5 tons of payload). The newly developed SAF 2906 and SAF3207 super super duplex stainless steel of Sweden Sandvik has super high strength and corrosion resistance, and the highest working temperature is 60 and 90, respectively.
One of the typical examples of the strength of duplex stainless steel is the wavy wall cargo tanks of chemical tankers. In 2002, the Hubei Qingshan shipyard used the UNSS3I803 (2205) wave panel made by Arcelor company to build the first 18500 DWT cargo tank for Belgian shipowners, and built many other vessels successively. In 2007, TISCO made the first domestic 2205 duplex stainless steel to provide the East Asia Shipyard with a cargo tank of 9000 tons (2205 tons, 600 tons), 5500 tons and 3750 tons. It has been used for 16 ships and is still in contract. 22-09 welding rod is also provided by domestic, but the welding wire still needs import. This is a great breakthrough, China classification society also has 2205 (S32205), 2507 (S32750) and copper (S32550) 2506 kinds of people into the standardized production.
The first is the application of bridge and concrete reinforcement, there are more than ten bridges in the world using duplex stainless steel, mostly walking bridge. Such as the first British York bridge and Sweden’s Aparte bridge are used 2205 steel, in recent years, the new bridge in Norway and Italy Rffolo bridge, has used the economical 2101 steel. Later, duplex stainless steels were also used in highway bridges, especially those that were sensitive to chloride induced corrosion.
The Brooklyn bridge in New York uses 2205 steel bars. The high strength and high elongation of the steel give it excellent fatigue resistance, and the service life is 2 times higher than that of the ordinary steel bars. The stonecutters bridge in Hongkong, China, uses 2000 tons of 2205 steel plates to make the outer surface of the upper part of the pylon. The service life is estimated to be 120 years without repair. Hongkong to Shenzhen cross Bay 3.2 km long highway channel bridge, about 1250 tons, 2205 and 316 used as high-speed road steel. In addition, Wuhan Tianxingzhou bridge for the public, railway cable-stayed bridge, 2205 10-20mm board produced 20 tons of TISCO, cutting, welding angle, as cohesive pier and cable-stayed steel components.
The second is the use of construction facilities, and Barcelona, Spain, uses 500 tons of 4mm thick 2101 to build flour storage. The United States will matt surface processing of AL 2003 1500 tons of sheet for building the world’s largest stainless steel roof (the roof of Doha International Airport, India, Qatar) by Outokumpu company provided 200 tons of electrolytic polishing surface of 2101 duplex stainless steel plate, made with 25mm, with 38mm, with 50mm three specifications 20 kilometer long pipe will be used. An Mumbai street overpass.
Source: China Pipe Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)