Application and development of duplex stainless steel

1 Overview

In recent years, the output of the world’s duplex stainless steel is growing, accounting for about 1% to 2% of the total stainless steel production. The output of China’s duplex stainless steel has grown significantly with the production of stainless steel (annual output of 6.943 million tons in 2008 and steel self-sufficiency rate of 82%). In 2008, the domestic crude steel output of duplex stainless steel was 16,867 tons. , an increase of 1.6 times over 2007.
With the commissioning of advanced process equipment, the specifications of China’s duplex stainless steel have also made great progress. For example, Taigang’s equipment has been able to produce 3000mm wide plate, 2000mm wide hot rolled coil and 0.6mm x 1500mm cold rolled coil. Baosteel can produce 4000mm wide plate and 1600mm wide hot rolled coil. For example, Zhejiang Yaang Pipe Industry Co., Limited. has built a full-automatically controlled steel pipe hot extrusion production line, which provides a possibility for the future production of super and even super duplex stainless steel pipes.
There has also been great progress in process technology. Taigang uses AOD furnace to smelt nitrogen-containing stainless steel, and establishes a nitrogen alloying process model, which can accurately control the nitrogen content in the finished product to reach ±0.0135%. In addition, the P and S content in the finished product can be controlled to a lower level. The performance of the series of duplex stainless steel products, especially the performance of high-nitrogen duplex stainless steels is guaranteed. In addition, the production process of duplex stainless steel plate has been mature, the production of hot and cold rolled coils of duplex stainless steel can completely reduce imports, and some large-diameter thick-walled tubes that have been successfully produced by some manufacturers such as Pangang Group have also achieved Breakthrough progress.
The advantage of duplex stainless steel is its superior corrosion resistance, especially resistance to localized corrosion. In the case of large fluctuations in nickel prices, the development of nickel-saving economical steel grades has become a key promotion product. On the other hand, in the harsh and corrosive environment, due to its high cost performance, the development of high grade steel grades has also become one of the important development directions. Another advantage of duplex stainless steel is that it has twice the strength and good toughness of austenitic stainless steel, which is the development goal of foreign duplex stainless steel in recent years, that is, not only used in the traditional papermaking and chemical processing industries. The equipment also utilizes its high strength and good fatigue resistance for important utilities such as bridges and road construction.
In the following two aspects of materials and applications, the development trend of duplex stainless steel in the development and application of steel in recent years is outlined.

2 Development trend of steel grades

Economical duplex stainless steel

There are three kinds of new mature steels developed abroad: one developed by Armco Nitronic of the United States and incorporated into the ASTM A240/A240M steel plate standard, under the designation UNSS32001, and the company code is 19D, which is a new steel grade that is not easy to produce δ phase. , has been used in deep sea pipelines and car frames. The other was developed by the Outokumpu company in Finland in 2002. The company name is LDX 2101. In 2006, it was incorporated into the US standard under the designation UNSS32101. It can be used to manufacture process equipment for medium corrosive environments, such as white liquor tanks in paper mills. wide. In recent years, special attention has been paid to the development of steel grades for infrastructure, and it has been successfully used in the construction of bridges and the like. The two steels are all made of Mn and N, which reduce the content of Ni and Cr. Their corrosion resistance and 304LH are cheaper because they do not contain Mo, but they are not suitable for the structure of the sea. The third is AL2003 steel developed by Allegheny Technologies of the United States, which has been incorporated into the US standard under the designation UNSS32003. It has a nickel content of 3.5%, is higher than the former two steels, and contains 1.7% Mo, which can be used for depths up to 1200m. The high-pressure pipeline system that transports sulfur-free or mild sulfur-containing oil and gas on the seabed.
Combined with the domestic resources, it is considered that this type of steel has development value. It is necessary to have a more promising economical dual-phase steel in a medium corrosive environment. Currently, development of LDX2101 steel is underway, and composition optimization and welding are required. In-depth study of process and performance.

super duplex stainless steel

The SAF2507 steel developed in Sweden is a widely used steel grade in super duplex stainless steel. It has been incorporated into many national standards. It has a good phase balance and is easier to master the production process in the same kind of steel, especially in the case of high chloride. It has excellent local corrosion resistance and is commonly used in seawater heat exchangers, pipeline cables in seabed oil fields, seawater desalination, flue gas desulfurization and other devices. The UK has developed Zeron 100 steel with W and Cu, which has been successfully used in seawater jet pumps, lift pumps, etc. due to its good wear and corrosion resistance. From a technical point of view: the offshore industry is a more meaningful place to use super duplex stainless steel, but in order to adapt to the current improved oil and gas recovery method, the wellhead control system requires higher corrosion resistance and the deep sea submarine temporary pipeline and pipeline cable. Demand, existing steel grades have been insufficient in strength and corrosion resistance, Sweden Sandvik company has designed a series of super super duplex stainless steel SAF2906, SAF2707HD, SAF3207HD and other high strength and excellent corrosion resistance up to 1000MPa Steel type.
At the same time, the United States Langley Alloys developed a sulfur content of 0.001%, the addition of copper Ferralium 225-SD50 steel, not only improved its resistance to pitting and crevice corrosion in seawater, its strength is also higher than other super duplex stainless steel 10 %.
In addition, recently developed for special applications, there are 29% Cr, 0.4% N SAFUREX new steel grades for Stamicarbon urea stripper, which can replace 2RE69 austenitic steel. In order to handle the chloride food tank, Japan has also developed NARDP-3W steel with 2% W, as well as DP28WTM steel with better corrosion resistance, mechanical properties, formability and weldability.

3 Promotion and expansion of applications

Duplex stainless steels are used in a wider range of applications, and have traditionally utilized their superior resistance to localized corrosion, especially stress corrosion resistance, as a corrosion resistant functional material. In recent years, from the perspective of its strength, the application of duplex stainless steel as a modern structural material deserves attention.

Chemical tanker

The wave wall cargo tank of a chemical tanker is also one of the typical strengths of duplex stainless steel. In the 1970s, France used the UR 5O (00Cr21Ni7Mo3Cu) steel without nitrogen to make the cabin. Today, Industeel and Arcelor Group received more than 70% of the UR 45N (2205) steel. Based on an in-depth study of the compatibility of stainless steel materials with cargo and the technical support of steel companies, UR 35N (2304) will also have a good development prospect.
In 2002, Hubei Qingshan Shipyard used the UNSS3I803 (2205) wave wall board produced by Arcelor to build a 18,500-ton chemical tank cargo tank for the Belgian shipowner, and several other ships were built one after another. Recently, Yangzi Shipyard signed a contract for the supply of 2205 duplex stainless steel by Outokumpu to manufacture four 3600-ton chemical tankers.
In 2007, TISCO first supplied the domestic 2205 duplex stainless steel to the Chuandong Shipyard to produce 9000 tons of cargo tanks (using 2,205 and 600 tons), 5,500 tons and 3,750 tons of cargo tanks. Contracts are still being signed for supply. 22-09 welding rods are also supplied domestically, but the welding wire still needs to be imported. This is a big breakthrough. China Classification Society has also incorporated 2205 (S32205), 2507 (S32750) and copper-containing 2506 (S32550) three steel grades into the human-level specification.

Building structure

•Bridge and concrete reinforcement
In recent years, there have been more than ten bridges in the world using duplex stainless steel, mostly pedestrian bridges. For example, the earlier York Bridge in England and the Aparte Bridge in Sweden used 2205 steel. In recent years, the new bridge in Norway and the Rffolo bridge in Italy have used the economical 2101 steel. Nearer duplex stainless steels have also begun to be used in highway bridges, especially those that are sensitive to chloride induced corrosion.
New York’s Brooklyn Bridge uses 2205 steel bars. The steel’s high strength and high elongation give it excellent fatigue resistance and life is more than 2 times higher than ordinary steel. The Stonecutters Bridge in Hong Kong, China, uses about 2,000 tons of 2205 steel plates to make the outer surface structure of the upper part of the pylon. The estimated life is 120 years from maintenance. From the Hong Kong to Shenzhen 3.2km long expressway bridge across the bay, about 1,250 tons of 2205 and 316 are used as high-speed road reinforcement. In addition, Wuhan Tianxingzhou Bridge is a cable-stayed bridge for both public and railway use. It uses 20 tons of 2205 10~20mm plates produced by Taigang, cut short and welded into angle steel, which is used as a component for connecting piers and diagonally-reinforced steel bars.
•Building facilities
Barcelona, Spain used 500 tons of 4mm thick 2101 to build a flour storage bin. In the United States, 1,500 tons of AL 2003 sheets processed by matt surface were used to build the world’s larger stainless steel roof (the roof of Qatar Doha International Airport). India provided 200 tons of surface electropolished 2101 duplex stainless steel sheets from Outokumpu. 2025mm, Ф38mm, Ф50mm three kinds of 20km long welded pipe, will be used for the handrail of the Mumbai street overpass.

Deep sea oil field

As the demand for oil and gas grows, driving operators to mine deeper and farther subsea oil fields has rapidly increased the use of deep-sea oil wells. The main production platform implements a standardized pipeline harness operation to provide water, power, decompression, and uphole communications from the well bore. In addition, in order to ensure the fluidity of the oil, injection of chemical agents is required in many deep-sea return pipes, and in order to increase production, oil well acidification is also carried out through pipeline cables. Pipeline cables have become the lifeblood of subsea mining systems. Facing the deep sea exposure environment means that the pipeline cable needs to be highly mechanical, resistant to internal and external corrosion, and resistant to stress corrosion cracking. The preferred material for deep-sea pipelines should be super and ultra-super duplex stainless steel, but due to price and manufacturing problems, galvanized 19D duplex stainless steel (ZCLDSS) has been developed, and the design life of the pipeline cable is 20 years. Has been promoted and applied. In addition, the economical low-nickel AL 2003 steel has also been used in 2006 for submarine pipelines with a depth of more than 1200 m in the East Malaysia oil field. The copper-added Ferrallium 225-SD50 duplex stainless steel has become the container material for 7000m deep seabed equipment and cables, and has been developed as a highly accurate subsea locator and controllable deep sea acoustic transponder pressure housing and load bearing components (7000m sea) Deep is about 700 atmospheres, HI 2.5 tons load). Sweden’s Sandvik’s newly developed SAF 2906 and SAF3207 super duplex stainless steels are ultra-high strength and corrosion resistant, with high operating temperatures of 60 and 90 ° C, respectively.

Other industries

•Seawater desalination
At present, the desalination industry is growing rapidly. Half of the plants are now in the Middle East. The more common methods of desalination have multi-stage flash (MSF) and reverse osmosis (RO). In recent years, advances in thin film technology have led to an increase in the use of RO. trend. The condenser tube of the MSF evaporator should use 2507 super duplex stainless steel tube instead of titanium or copper-nickel alloy. The flash chamber housing can be used 2205, which has been adopted in Libya. The high pressure pipe of the RO method and the high pressure pump of the high chloride environment are made of 2507 steel, which is comparable to the austenitic steel with 6% Mo and has been used in the newly built Ashkelon plant in Israel. The project on Caofeidian in China is to use a 300-ton 2205 steel plate supplied by Outokumpu to make a multi-stage flashing device of 1OOm×25m×6m. Usually 1.2 million tons of processing equipment requires 10,000 tons of 6mm thick steel plates. China’s fresh water resources are insufficient, the coastline is long, and desalination will be put on the agenda, which will be the potential use of duplex stainless steel.
•Fume desulfurization (FGD)
The FGD system is used to eliminate SO2 from flue gas from coal-fired power plants, reduce emissions to the atmosphere, and prevent acid rain. Forecasts indicate that two-thirds of the world’s coal-fired power plants will be equipped with FGD units by 2020. At present, the wet FGD device is dominant, mainly using limestone mud to neutralize and clean the exhaust gas in the absorption tower. At the population of the device, the high-temperature exhaust gas forms a high concentration of high-temperature sulfuric acid, and a high-molybdenum nickel-based corrosion-resistant alloy is required. However, after reacting with the lime mud, the pH is raised and the temperature is lowered. At 55 ° C, pH > 6, Cl – concentration below 30,000 ppm can choose 2205 steel, better than 317LMN effect. Super-phase duplex stainless steel can also be used if the Cl- concentration is higher and the pH is lower. The Coleson Cove Power Plant in Canada is based in the United States on the top of the absorption tower with 360 tons of 2205 duplex stainless steel. Most of China is a coal-fired power plant, and a large number of FGD systems will open up a new market for duplex stainless steel.
The 1.4475 wear-resistant and corrosion-resistant duplex stainless steel GX150CrNiMoCuN41-6-2 developed in Germany is composed of a network of high-chromium carbides with a volume of 25% to 30%, which improves the wear and corrosion resistance. The impeller used in the Niederau β em power plant for the manufacture of FGD recirculating filter pumps works well with solid particles up to 25%, pH > 4 and chloride content 5.5%.
The above is the progress in the application of foreign countries in recent years. Some domestic ones have just begun, and some have not yet been put on the agenda. For many years, Taigang has provided 2205 composite plates for the Three Gorges and Wanxian, Lantian and other plants in water conservancy projects and salt production. Fortunately, TISCO has been able to provide super duplex stainless steel 2507 composite plates for coking projects. Zhenhai Refinery uses 2205 welded pipe instead of heat exchanger made of seamless pipe. The welded pipe made of 1m×6.5mm plate is used as the conveying pipe in Guangxi Million Ton Refinery. This is a new breakthrough in the refinery. Development prospects. At present, the manufacture and use of plate heat exchangers have been put on the agenda, which puts new demands on domestic cold rolled coils. In recent years, Baosteel Wugang Co., Ltd. and Special Stainless Steel Co., Ltd. and Jiuli Group Co., Ltd. have also provided seamless steel pipe replacement for the West-East Gas Pipeline Project. Pangang Group Chengdu Iron and Steel Co., Ltd. successfully produced 295mm × 45mm large diameter thick Wall pipe, Wujin Stainless Steel Pipe Factory has already mass-produced Ф108~25mm×3~10mm steel pipes of 2205 and 2506 steel. In addition, in terms of exports, China’s pulp evaporating tanks manufactured by Indonesian paper mills, the 800 tons of 2,304 plates and the renewed 2000 tons of plates required for the first phase of the outsourcing project are all supplied by Taigang and supplied to the Dutch ship propellers. The board also has hundreds of tons of 2304 steel plates. The potential use of duplex stainless steel is very wide and it remains to be developed in China.

4 Suggestions for developing duplex stainless steel in China

To promote the development of duplex stainless steel in China, the following are recommended:

  1. Use a variety of propaganda methods to increase publicity.
  2. Key development requires large quantities, widely used, and more mature craftsmanship, such as 2205, 2304 and other conventional steel grades. Actively promote the production and application of economical duplex stainless steel such as 2101. Further research and development of special super duplex stainless steel to meet the needs of higher corrosion resistance, higher strength and higher temperature. In terms of use, in addition to continuing to develop in the fields of water industry, petrochemical, salt production, chemical tankers, etc., it is necessary to expand heat exchangers, containers, and storage in oil and gas, environmental protection, seawater desalination, marine engineering, building structures and manufacturing. The development of industrial uses such as tanks and the development of potentially huge civilian markets.
  3. The current domestic main products are medium and heavy plates produced by single-roll mills. In order to improve efficiency, hot-rolled coils (shear plates) are produced by continuous rolling and hob rolling mills. The key to expanding the application is to speed up the trial production and supply of thin gauge cold rolled duplex stainless steel coils. It is also necessary to accelerate the production and development of pipes, long products, and supporting products such as castings, forgings and welding consumables.
  4. Master the welding process characteristics and welding materials of duplex stainless steel and austenite.
  5. Organize the joint research of upstream and downstream enterprises and production and research institutes of production enterprises and units, strengthen the exchange of technology at home and abroad, and promote the development of duplex stainless steel.

Source: China Stainless Steel Fittings Manufacturer – Yaang Pipe Industry Co., Limited (www.yaang.com)

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