Feature

Innovations in Stainless

Posted on 09 February, 2010 | Tags: Spotlight

Duplex grades of steel are preferred by the industry over austenitic grades for various industrial applications. Industry is switching over to Duplex Steel for its high resistivity to different forms of corrosion, high strength and low nickel content that make it a feasible option to be used as the material of construction over a wide range in the process industry.

The word duplex is based on the concept of austenite and ferrite formulated in the same material. Duplex stainless steels combine many of the beneficial properties of ferritic and austenitic steels. Due to their high content of chromium, nitrogen and often molybdenum, these steels offer good resistance to local and uniform corrosion. The duplex microstructure contributes to their high strength and high resistance to stress corrosion cracking. Duplex steels also have good weldability.
Duplex grades have proved to be superior in comparison with austenitic grades in many of industrial applications. Because of their low nickel content, these grades are affordable and offer better price stability than the austenitic grades of stainless steel. The strength of Duplex grades - close to 90 percent higher than that of Austenitic grades - allows for the use of considerably thinner materials, resulting in major weight and cost savings. (Refer, design case given in Table-1)
The table clearly shows a Weight saving of 38 % by using LDX2101 besides the price advantage.

Scope of Application
Duplex steel has a wide scope for industrial applications because of excellent properties that gives the equipment a long life and the equipment can perform consistently for a long time. Equipments get exposed to highly corrosive environments in the chemical process industry. This steel has high strength and offers high resistance to different types of corrosion that usually occurs. Duplex Steel offers good resistance to pitting and crevice corrosion. This is highly resistant to stress corrosion cracking and corrosion fatigue and offers good resistance to uniform corrosion. Duplex Steel also offers good erosion and fatigue resistance. Other properties include its capacity of high energy absorption, low thermal expansion and good weldability. Outokumpu Stainless produces a whole range of the lean alloyed LDX 2101 up to the super duplex grades SAF 2507 and 1.4501.
These duplex grades are used extensively for wide range of applications by the process industry. Some of the applications are as follows:

• Heat exchangers
• Water heaters
• Pressure vessels
• Large storage tanks
• Rotors, impellers and shafts
• Components for structural design
• Firewalls and blast walls on offshore platforms
• Digesters and other equipment in the pulp and paper industry
• Cargo tanks and pipe systems in chemical tankers
• Desalination plants
• Flue-gas cleaning
• Seawater systems

Recognized by Industry
Many industries in the West have switched over to using Duplex Steel as the material of construction. This is now gaining popularity in India also and the industry is aware about the edge that this offers over other conventional materials of construction in the process industry.
Some of the case studies are illustrated below where Duplex Stainless Steel has achieved recognition and created a revolution in Duplex applications.

Pressure Vessels
The new hydrogen peroxide reactor at Smurfit Kappa Kraftliner Piteå in Sweden is the world's first industrial-scale pressure vessel built entirely out of LDX 2101® (EN 1.4162) plate. Duplex Stainless Steel grade LDX 2101® has revolutionized the pulp industry with a breakthrough for pulp bleaching.
LDX 2101® replaced the high performance , high alloyed austenitic stainless steel grade 904L (EN 1.4539) and more commonly used Duplex 2205 (EN1.4462). LDX 2101®, has very low nickel content, is well adequate to handle the hydrogen peroxide reactor process, an environment with a low corrosion rate under alkaline conditions but high pressures up to 10 bars and temperatures around 110 degrees Celsius.
The main reason for the selection of this grade for the new reactor was its high strength, which allowed the designers to use thinner gauges compared to traditional grades. That and the low nickel content of LDX 2101® brought considerable cost savings. Additional benefits to the tank fabricators came from the good machinability of LDX 2101®. The contractor at the site expressed surprise at the easiness of the fabrication process.

Edible Oils
Loders Croklaan used LDX 2101® duplex stainless steel, for their Palm Oil tanks because of high corrosion resistance offered by all the grades. Duplex as a material of construction helps safeguard the tank content by reducing the risk of cross contamination. Moreover, as LDX 2101® has 90 percent higher strength than standard austenitic stainless steels, the material enabled to achieve a 30 percent weight saving compared to a conventional stainless steel tank.
Extra wide material is another benefit that the user gets from Outokumpu. The company provides duplex stainless steel in 2-meter-wide coils and tailor-made plates up to 3.2 meters wide. The large widths translate into cost savings due to fewer rings and less welding. LDX 2101®, a low-alloyed duplex grade, is ideal for moderate corrosion conditions such as storing palm oil and other edible oils. LDX 2101® can well compete in price with carbon steel tanks when the lifecycle cost is taken into account because of its low nickel content. Because of excellent corrosion resistant properties and cost competency LDX 2101® is the best available option to store palm oil.

Desalination
Duplex stainless steels have emerged as optimal materials for desalination. Outokumpu pioneers in Duplex applications having first introduced the idea of solid Duplex Evaporators and now offers "DualDuplex™" - for evaporators. Selection of grade 2205 Duplex Steel (EN 1.4462) for solid Duplex Evaporators came as a breakthrough for the concept of Duplex steel. The evaporators were required to be installed in the Melittah MSF plant in Libya that was being built by Reggiane of Italy. The plant with 4 MIGD capacity was commissioned in 2004.
Duplex desalination evolved and the next stage was initiated in 2004. Outokumpu proposed the DualDuplex ™ concept. The cocept is based on usage of two different types of Duplex in the structures of evaporators. Highly corrosion resistant grade 2205 is applied for the parts that are exposed to the most hostile conditions and Duple LDX 2101® (EN 1.4162) or Duplex 2304 (EN 1.4362) for parts exposed to less hostile conditions. LDX 2101® provides good corrosion resistance and high strength. This has low nickel content so it has the advantages of a lower price and better stability than high-nickel stainless steel.

Waste Water Treatment

Although stainless steel is a relatively new material in waste water treatment, but it is fast becoming the standard in plant hardware owing to needs to fight corrosion and abrasion while lowering maintenance needs and life cycle costs.
Confederación Hidrográfica del Norte planned to set up a wastewater treatment plant with a minimum plant life of twenty five years. The company had specified the austenitic grade EN 1.4404 (ASTM 316L) for gates, suction precipitator bridges, sand removers and lamellas.
By the time Cadagua took over engineering of the project on 2006, sufficient time had elapsed from the time of planning till the execution of project. The rates of steel that were specified initially had skyrocketed by then because of high nickel prices. To find a suitable alternative, Outokumpu was approached by Cadagua for their unique capabilities in offering Duplex grades for various industrial applications and expertise in offering solutions for Desalination projects.
Based on corrosion tests E.D.A.R de Bens, Cadagua and the project contractor were convinced about Duplex 2304 (EN1.4362) as the right material of construction for the desired project. Outokumpu bagged the contract to supply approximately 360 tons of Duplex 2304 sheet and plate to the wastewater treatment project.
In addition to cost savings, Duplex 2304 offer the water utility companies multiple benefits in comparison with EN 1.4404 grade. Moreover, it has higher capability to withstand abrasion caused by solid suspended particles because of high surface hardness. Additional benefits include thinner material gauges and consequently lighter structures translate into less edge preparation. There is lesser need for welding consumables and thus fewer welding hours. Overall it is easier to handle the structure and requires lower capacity cranes. Duplex as a material of construction for the water treatment plants lowers life cycle costs and promises even longer usable lives.

Biofuels
Tank fabricator Oostwouder Tank- & Silobouw BV of the Netherlands had to build 66 tanks for its client Noba Vetveredeling BV in a large-scale biofuel project in the Port of Amsterdam. They chose Outokumpu's Duplex LDX 2101® for the company's largest tank project to date.
Oostwauder already had the experience of using low-nickel Duplex grade LDX 2101® by Outokumpu. They decided to choose this grade for main parts of the tank because of high mechanical strength offered by Duplex steel that is almost twice as offered b austenitic grade EN 1.4301 (ASTM 304) and value for money because of lower nickel content. Total of 1500tons of material was required for the project. Because of surges in nickel prices LDX 2101® has emerged as the more economical choice compared to higher-nickel grades. In addition to the price advantage, Oostwouder achieved a 25% material weight saving by using LDX 2101® compared to austenitic grades.
Oostwouder's Managing Director Jan Piet Oostwouder explained that tank engineering requires a certain minimum material thickness that does not allow fabricators to take full advantage of the strength of Duplex grades, as compared to some other applications where the weight saving could be even greater. For the bottom part of the tanks, where a higher level of corrosion resistance is needed, Oostwouder uses Outokumpu's Duplex 2304.Outokumpu has been a long-term supplier for Oostwouder.

Storage Tanks
Empyro builds large tank farms that are a revolution in tank storage. The company sources Duplex LDX 2101® stainless steel from Outokumpu for all the tanks to achieve major cost savings. The company observed the weight reductions that resulted in significant cost savings while setting up the project for Relisa. The company saved almost 200 tons in the first thirteen tanks that were built using 1350 tons of LDX 2101® plate. Later the company saved approximately 150 tons while building 9 new tanks that required 730 tons of LDX 2101®.
At a time when the nickel prices are soaring LDX 2101® comes as a cost effective and durable alternative for austenitic stainless grades.

Yatinder Pal Singh Suri  is Country Head, Outokumpu India Private Limited.  
Email Id : yatinder.suri@outokumpu.com