Applications of Duplex Stainless Steel

Flue gas desulfurization
In order to further reduce SO2 emissions from coal-fired power facilities, flue gas desulfurization (FGD) is a method to achieve low SO2 emissions. "Wet scrubbing" SO2 from flue gases using lime or limestone slurry is a mature technology that has been used as a basic method in utility boiler systems since the 1970s.

Flue gas desulfurization device made of 2205 duplex stainless steel
Modern scrubbers can currently remove 90% of SO2 from exhaust gases. Modern FGD units consist of several zones with different temperatures, chloride contents and pH. 2205 stainless steel (S32205) is already used in FGD units in Europe and Asia due to its lower cost and better corrosion resistance compared to austenitic stainless steel. Recently, North America has embraced the use of duplex stainless steel, which has become the most popular material of choice for FGD absorber towers due to its high post-weld strength, good corrosion resistance and high toughness.

Desalination
Seawater desalination requires materials to withstand the most stringent test due to its high chloride content, high temperature and corrosive process environment. The history of desalination is essentially a history of materials development, as desalination customers balance corrosion resistance requirements with the need to keep investments affordable. In early desalination projects, the evaporators of multi-stage flash (MSF) and multi-effect (MED) desalination equipment were made of carbon steel. Later, MSF evaporators were generally clad with 316L (EN1.4404) austenitic stainless steel. The MED evaporation chamber was first coated with epoxy resin and later covered with stainless steel.

Multi-stage flash seawater desalination device made of S32101 and S32205 duplex stainless steel
The benefit of using duplex stainless steel is that its high strength is twice that of conventional austenitic steel grades combined with high corrosion resistance. As a result, duplex stainless steel evaporators can be manufactured from thinner steel sheets, requiring less material and welding. Further benefits include ease of disposal and lower overall impact on the environment.

Petroleum and natural gas
In the oil and gas industry, duplex steels play a vital role in helping to withstand harsh conditions. Duplex stainless steel is mainly used in fluid pipes, process pipeline systems and equipment, such as separation devices, washing devices and pumps. Subsea, these materials are used in downhole production pipes, fittings and manifolds, fluid pipes and pipelines transporting corrosive oil and gas. Super duplex stainless steel (25% Cr), due to its effective resistance to design stress, is often used in the following areas: round bars, forgings, castings, thin plates, thick plates, pipes, fasteners, etc.

2507 Umbilical Cables for Offshore Oil and Gas
Super duplex steels also have excellent fatigue resistance and good galvanic compatibility with other high-alloy stainless steels. Umbilicals are used to control wellhead operations using hydraulic lines and can also be used for chemical injection. Since the introduction of steel umbilicals into the market, duplex stainless steel has been the most commonly used material. In recent years, the trend of developing deep-sea oil and gas fields requires longer umbilicals. Improving the strength of the material reduces the weight of the umbilical and allows for longer lengths. Biofuels
The biofuel industry (especially ethanol) is a growing area for duplex steel applications. 2205 stainless steel has been used in Singapore’s biomass oil NExBTL process equipment. In a large-scale biofuel project in the Port of Amsterdam, Dutch storage tank manufacturer Oostwouder Tank-&Silobouw BV selected S32101 for the oil depot manufactured by Noba Vetveredeling BV. S32101 was also specified for the manufacture of vessels and pipes at the Agroetanol ethanol plant expansion project on the Swedish island of Händelö. Economical duplex steels have been used to replace 300 series austenitic stainless steels in many ethanol plant applications.

2205 kraft pulp continuous digester and impregnation tower at Swedish pulp mill Food and drinks
Economical duplex steels are also proving their worth in the food and beverage industry. The material is used in two projects in Spain, a food storage and a wine storage. At the Port of Barcelona, Emypro SA uses all S32101 to build food storage tanks, replacing EN1.4301/1.4307 (304/304L). In Demières, southern Spain, duplex stainless steel was used for the first time in a wine storage facility built by Spanish tank manufacturer Martinez Sole for Garcia Carrion.

2507 stainless steel falling film evaporator, TMR stainless steel

construction industry
Duplex steel continues to play an important role in the construction of bridges, which are used in corrosive and salty environments while requiring high load-bearing strength. Two recent examples, both from Asia, are the Stonecutters Bridge in Hong Kong and the Double Helix Pedestrian Bridge in Singapore, both of which use 2205 duplex stainless steel. In 2006, the Stonecutters Bridge used 2,000 tons of 2205 duplex steel plates and tubes, with the surface sections constructed from custom-sized plates by a manufacturing plant in China. The panels are polished and shot-peened for optimal reflectivity during the day and at night.

Singapore Double Helix Pedestrian Bridge, constructed of 2205 duplex stainless steel
In addition, 570 tons of duplex stainless steel was used for the double helix pedestrian bridge. The bridge’s stunning design incorporates two helical tubular stainless steel sections resembling a DNA structure, with its double helix support structure using 2205 duplex steel tubing and plate respectively. The stainless steel surface provides evening illumination by reflecting light, which is used to enhance the design.

Duplex stainless steel roof for new Doha International Airport
The world’s largest stainless steel roof at the new Doha International Airport in Qatar is constructed using economical duplex stainless steel (S32003) containing molybdenum. The terminal's most prominent feature is its corrugated roof, said to be the largest stainless steel roof in the world. The roof area is approximately 195,000 square meters, and approximately 1,600 tons of duplex stainless steel were used. Several factors are considered when choosing a stainless steel grade, the most important of which is the distance of the airport from the sea. Not only does the roof have to withstand the heat and humidity of the Middle East, it also has to withstand salt corrosion. Compared with other steel types, duplex stainless steel has cost and a good strength-to-weight ratio.