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Material for Winning Ideas Outokumpu Duplex Stainless Steels DUPLEX

Duplex Stainless Brochure

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Material for Winning IdeasOutokumpu Duplex Stainless Steels

Du

ple

x

Contents

What’s your winning idea?

Outokumpu is fast becoming the undisputed number one in stainless. What makes us special is total customer focus – all the way, from R&D to delivery. You have the idea. We offer you world-class stainless steel, technical know-how and support.

Outokumpu Duplex – more strength, less material

Outokumpu Duplex allows you to realise your most demanding projects: thanks to its superior strength, you can sometimes manage with even 50% less material, which means considerable cost savings. Outokumpu Duplex is a highly environmentally

Find out how the right material choices can save enormous costs and accelerate your business in the long run. See inspiring case studies from around the world.

BuSineSS & trenDS

Winning the future

Duplex revolution

Case studies

When to go with Outokumpu Duplex

What makes Outokumpu Duplex such a strong material? How to weld and form duplex? See in-depth technical information and enjoy our tips for best results.

COmpOSitiOn anD BenefitS

Chemical composition

Mechanical properties

physical properties

Corrosion resistance in various environments

Advice for fabrication

product assortment

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Case highlights

Trend-setting duplex tank farm

See how relisa S.a. managed to reduce construction material by up to 50%. See page 9.

Benefits in mass production

Duplex is the material used for the water heaters of Kingspan Hot Water Systems Ltd. making them both easier to handle and cheaper to produce. See page 10.

Reinforcing the present

Brisbane’s six-lane Gateway Bridge is reinforced with Outokumpu Duplex on its most critical parts, ensuring a design life of 300 years. See page 11.

Building the future

the marina Bay pedestrian Bridge in Singapore is stunning in architectural design, taking advantage of the possibilities of Outokumpu Duplex. See page 12.

Activating your ideas

• pre-fabrication according to your needs

• Suggestions for material replacements

• Computer simulations and calculations to ease design work

• On-site testing options and administrative help

sustainable material with significantly longer service life in corrosive environments when the proper material selection is made.

See interesting case studies and read all about material properties as well as fabrication hints for Outokumpu Duplex. Together, let’s turn your winning ideas into a successful project.

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The use of stainless steel is increasing fast due to the material's durability, corrosion resistance and aesthetics. If the right grades are selected, stainless steel lasts even hundred years. In the long run, stainless steel is also often the least expensive material, thanks to low maintenance costs.

Winning the future – useful answers for future challenges

for the environment is simply not accepted anymore. Environmental responsibility and legislation have an increasing impact on companies’ operations in every industry. Proof of responsibility is demanded for the whole life cycle of the product. Those who can offer action instead of words in social and environmental responsibility will be the winners of tomorrow.

Outokumpu Duplex is an environmentally sound choice from many different viewpoints:

• It uses recycled steel as main raw material and it is 100% recyclable.

• Very low level of metal ion is released in to the environment.

• Less need for hazardous coatings.• Thanks to high strength, it is possible to reduce the

weight of the structures and therefore lower energy consumption in transport, construction and usage.

Trend 3:

ensuring safety, pleasing to the eye

In addition to corrosion-resistance and durability, constructors face increasing demands for a human approach: it is not enough anymore that the tanks, vessels and buildings “do their job”. They need to be safe for both the builders and the employees and be aesthetically pleasing. Outokumpu Duplex makes it possible to fabricate strong, fascinating structures while reducing the total weight.

Trend 1:

Global economics and striving for stability

When it comes to economics, all parties seek stability. In large-scale construction projects, right material choices can multiply savings. Outokumpu Duplex stainless steel has excellent strength, which can often mean the same structure can be built with less material: for example, tank walls can be considerably thinner. Compared to other grades with comparable corrosion resistance, also the nickel content of Outokumpu Duplex is very low. This means more price stability, less surprises and easier budgeting.

Trend 2:

Rising environmental awareness

In previous years, temporary structures built for world fairs and events for example, could be demolished after the event. Such a waste of labour and disrespect

Montanstahl’s head office with sculptures by

Helidon Xhixha on the left. Courtesy of Montanstahl.

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Low nickel content for price stability

Wide range of applications

thinner material and therefore possible lower cost

Good corrosion resistance

High strength

More strength, less material

Put simply, the benefit of Outokumpu Duplex lies in weight reduction. You gain more strength with less material. Below, you can see an example of what happens when standard austenitic steel is substituted with Outokumpu Duplex.

Calculate your weight savings on the Internet

Steel professional tool at www.outokumpu.com offers interactive tools for materials selection, rough estimation on wall thickness calculations etc. Visit our website and learn more!

less material means benefits in every step of the project

With Outokumpu Duplex, you can purchase, transport, weld and assemble less material. When thinking of the cost of labour, savings can be tremendous.

Tank CosT eXaMple 1:

Austenitic steel versus Outokumpu Duplex

When the same tank is manufactured from Outokumpu Duplex instead of conventional austenitic steel, the biggest savings are made in manufacturing phase, thanks to less amount of material needed. The tank walls can be significantly thinner, yet safe in use.

Tank CosT eXaMple 2:

Carbon steel versus Outokumpu Duplex

When the same tank is manufactured from Outokumpu Duplex instead of carbon steel, the biggest savings come in the maintenance phase: carbon steel needs to be properly protected in the manufacturing phase and again after certain periods of usage. All this means extra labour, which can be avoided using Outokumpu Duplex.

4301 ldX 2101®

plate thickness 5-12 mm 5-7 mm

Material cost* 144 keUr 108 keUr

Welding cost** 55 keur 35 keur

Labour cost** (Welding and tank assembly)

89 keur 49 keur

Total manufacturing cost 144 keUr 84 keUr

Total initial cost 288 kEUR 192 kEUR

Potential cost saving ~33%tank size: diameter 18.5 m, height 18 m. *Based on Outokumpu price list per 19 Oct 2009. **Based on actual costs provided by a Swedish Contractor 2008.

Carbon steel ldX 2101®

total initial cost* 192 keur 192 keur

Surface protection cost 100 euro/m2

x 1000 m2

no surface protection required!

elapsed time between maintenance events

15 years

Life cycle duration 30 years 30 years

Operating cost 64 keur 0 keur

Total LCC 256 kEUR 192 kEUR

Potential cost saving ~25%tank size: diameter 18.5 m, height 18 m.*assume equal intitial cost level: lower material cost for carbon steel equals the measures for protecting the plate surfaces for a tank designed for aggresive environment.

Duplex saving potential compared to austenitic grades.the curve will shift depending on grades compared and actual price level.

Potential savings with Duplex compared to austenitic grades

Weight saving

Savings in costs

0%

10%

10% 20% 30% 40%

-10%

20%

30%

40%

Great combination of both high strength and adequate corrosion resistance.

Positioning of Duplex grades

Pipes: reductions in wall thickness and weight between grades 1.4307 and LDX 2101®

Design datapressure = 16 barTemperature = 50°Cod = 610 mm

required pipe length = 1000 mMin WT acc to en 13480-3:Weld factor z = 0.71.4307 = 5.8 mmldX 2101® = 2.9 mm

Grade 1.4307WT = 6.0 mmWeight = 90 tons

Grade LDX 2101® WT = 3.0 mmWeight = 45 tons

Case: Duplex as a substitute for austenitic in storage tank

[mm]

[m]

18

16

14

12

10

8

6

4

2

123456789101112

430161.5 ton

LDX 2101®

43.5 ton

Required thickness austenitic

Required thickness Duplex

LDX 2101®

150

0 10

43074404 4438 904L

254 SMO®

4565

2507

4436

2304

2205

LDX 2404™

4439

20 30 40 50 60 70 80 90

200

250

300

350

400

450

500

550

600

Du

ple

x

Rp

0,2[

MPa

]

Corrosion Resistance, CPT typical

Hot coil

Au

sten

tic

6 7

Relisa S.A. of Spain stores liquid foods and chemicals in a new tank farm at the Port of Barcelona: Spanish storage-tank fabricator Emypro S.A. has built the entire farm, consisting of 22 units, using Outokumpu Duplex LDX 2101® plate. When engineering the first phase of the farm, Emypro could see the advantages of the duplex grade and partnered with Outokumpu to convince Relisa.

Trend-setting duplex tank farm – up to 50% weight savings

Duplex revolution – examples of ideas in action

Avesta Jernverk AB of Sweden, today part of Outokumpu, produced its first commercial duplex alloy in 1930. Avesta 453S, contained 26% Cr, 5% Ni and 1,5% Mo, and was in the beginning used as so called acid proof material in the production of sulphite pulp.

However, its higher strength was immediately noticed and then tested with certain components that were subjected to wear, such as spindles, pumps and shafts. When industries developed further, the possibilities of duplex truly opened up.

To date, Outokumpu Duplex has proven its worth around the world. We are proud of the masterpieces realised by our customers.

As Emypro was putting the finishing touches to the tanks, Relisa ordered 9 more using the same grade. The grade selection has offered the fabricator and tank owner major competitive advantages thanks to the qualities of LDX 2101®. The grade’s strength is almost twice that of standard austenitic grades. This has al-lowed Emypro to achieve major reductions in material quantities compared to the austenitic alternatives 1.4301/1.4307 (304/304L). The total weight saving is more than 20%, in some sections of tanks, even up to 50%.

Technical highlights

Outokumpu Duplex has good weldability, and the material supports most known welding techniques. See welding tips on page 20.

Interesting facts

Emypro’s and Outokumpu’s pioneering development continues a history of milestones achieved together, including the world’s largest duplex storage tank (22 m in diameter and 25 m in height) fabricated using Outokumpu Duplex grade 2304.

Celtic Gateway footbridge united Kingdom

Storage tank farmGold Bridge, China

Road tankers indox, Spain

World’s largest digester Jinhall mill, China

Bilbao Bridge Spain

Natural gas flowlineSosta, Oman

Storage tanksemypro, Spain

Desalination plantSiDem

Stainless racing motorcycle Highland Group, Sweden

Tank farm Oostwouder, the netherlands

Biofuel plant expansionagroetanol, Sweden

Clean coal technologyenel, italy

Trend-setting tank farm relisa, Spain

Bioethanol fermentation tanks Cital, italy

Courtesy of emypro

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Built to last for 300 years

Brisbane’s six-lane Gateway Bridge will be duplicated as part of the Gateway Upgrade Project. This is the largest road and bridge project in Queensland’s history, delivered by Queensland Motorways with design and construction by the Leighton Abigroup Joint Venture. Looking to the future, the new bridge will have a design life of 300 years.

To ensure such a long lifespan, the bridge will have stainless steel reinforcement bars (rebar) in the most critical bridge structures; the pilecaps located in the splash zone of the Brisbane river. Leighton Abigroup Joint Venture approached Outokumpu as they were searching for a stainless rebar supplier. We are one of the leading producers of stainless steel long products in the world.

Based on their thorough expertise and due to stainless steel prices at the time, the bridge engineers set out to find a low nickel content stainless steel, such as Outokumpu LDX 2101®. The next task was, with the help of Outokumpu, to convince the customer that LDX 2101® had the required characteristics for the environment. Based on concrete mix properties and the corrosion resistance of LDX 2101®, the result was a concrete cover of 75 mm, more than enough to match the demanding durability requirements. The result was a cost efficient and durable solution for the customer.

Technical highlights

Outokumpu Duplex has excellent resistance to atmos- pheric corrosion, which is caused by harsh conditions that can be found, for example, in industrial sites, near the sea and in big cities. Read more on page 19.

Interesting facts

In the United States, corrosion is estimated to cost close to US$ 300 billion per year, eating away 3-4 % of GDP. As much as 40 % of this could be prevented. Corrosion of the carbon steel reinforcement is the main reason why structures show premature failure today. The annual direct cost of corrosion to bridges alone in the USA, is estimated to be US$ 5.9 billion to US$ 9.7 billion1. If indirect costs were to be included, i.e. loss of economic revenue, the report forecasts that this could be as much as ten times higher. In Western Europe, the figures are not much better, an estimation in a Nordic report stated that € 5 billion is spent yearly for repair of corroding concrete infrastructures2.

References:1 B. Elsener, L. Bertolini, R.B Polder, P. Pedeferri, Corrosion Of Steel In Concrete Prevention, Diagnosis, Repair, John Wiley and Sons Ltd., Weinheim, 2004.2 D.B. McDonald, D.W. Pfeifer, Y.P. Virmani, Corrosion-resistant reinforcing bars Findings of a 5-year FHWA Study. Int. Conf. Corrosion and Rehabilitation of Reinforced Concrete Structures. FHW, Orlando 7–11 December 1998.

When your household needs a water heater, it’s a question of reliability, right?

Manufacturers often want to give their products warranties for longer periods even up to 30 years, so it is understandable that they seek undisputed quality in their materials. Kingspan Hot Water Systems Ltd, a long-term customer of Outokumpu, is a market leader in high performance hot water storage solutions throughout the United Kingdom and Ireland.

Kingspan wanted to find a more cost efficient alternative to mild carbon steel and copper, which have been the industry standards for 50 years. The answer was Outokumpu Duplex: it gives pioneering manufacturers such as Kingspan a clear competitive edge. The strength of the material allows at least a 30% wall thickness reduction, making the boiler both

Multiplying benefits in mass production

easier to handle and cheaper to produce. The benefits multiply in mass production. Warm water in thousands of households is ensured for years to come.

Technical highlights

Outokumpu Duplex offers excellent resistance to stress corrosion cracking. Read more on page 18. Interesting facts

Water quality differs around Europe, and Outokumpu can offer grades to match Kingspan’s needs. LDX 2101® or 2304 are perfect for European water quality. For more demanding environments, 2205 is recommended.

Courtesy of kingspan Hot Water systems ltd.

Courtesy of leighton abigroup Joint Venture aBn.

10 11

Building the Future project checklist – when to go with Duplex?

The Marina Bay Pedestrian Bridge in Singapore, stunning in architectural and engineering design, will both link key sites of development and be an attraction in itself, symbolising Singapore’s aspirations as a biomedical hub. Nearly 300 metres long, the bridge is unique in many ways. It is composed of two spiraling tubular stainless steel members, resembling the structure of DNA. According to the designers, the DNA-like structure symbolises “life and continuity, renewal and growth”.

The stainless double-helix structure takes bridge architecture and engineering to entirely new directions. The inner spiral of the double helix is used to support fritted-glass and stainless-steel mesh canopies to provide shading to pedestrians. The bridge engineers selected Outokumpu Duplex 2205 (EN 1.4462) as the appropriate stainless grade for the

Are some of the characteristics listed below relevant for your application? Then Outokumpu Duplex might be your material of choice.

double-helix and support structures. In the hot and humid, maritime climate of Singapore, this highly corrosion resistant grade ensures low maintenance costs and good appearance during a service life of at least 100 years. The high strength of duplex 2205 also enables the development of a cost-efficient design. This duplex contract follows a series of demanding bridge projects worldwide for which Outokumpu has supplied duplex stainless products in several different grades.

Technical highlights

With the right tools and parameters for equipment, duplex grades can be shaped in to exciting and functional forms. Read more about forming of Outokumpu Duplex on page 22.

Interesting facts

The stainless steel surfaces will provide spectacular night-time illumination by reflecting a series of lights programmed to enhance the design.

Demands for materialresistance to uniform corrosionresistance to pitting and crevice corrosionresistance to stress corrosion cracking and corrosion fatiguehigh mechanical strengthgood abrasion and erosion resistancegood fatigue resistancehigh energy absorptionlow thermal expansiongood weldabilitywithin temperature range -40 °C to + 250-325°C*pressure vessel, beams

No need for sharp bend radiusdemanding forming techniques

Courtesy of Urban redevelopment authority, singapore.

*max temperature = 250°C in en10028-7, max temperature = 325°C in aSme ii-D 2007.

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What makes Outokumpu Duplex such a strong material? The secret lies in connecting the best of both microstructures: mixing austenite and ferrite. The result is two crystallographic phases, each with a composition sufficient to make it corrosion resistant. The phases in duplex grades are a body centered cubic phase (ferrite), and a face centered cubic phase (austenite). Favorable properties of both phases can be utilised in one alloy.

The chemical composition of duplex grades gives good corrosion resistance and desired mechanical and physical properties. Outokumpu can supply you with stainless grades especially designed to meet your needs.

Alloying elements and their purposeChromium makes it stainlessAt least about 11% chromium has to be added to a steel to form the passive layer that makes it stainless. These contents improve the corrosion and oxidation resistance. Outokumpu Duplex steels have a high chromium level, between 21.5 and 25%.

Nickel adds toughnessNickel obtains the desired phase balance and provides toughness. Duplex steels contain a relatively small amount of nickel, between 1.5 and 7%. If corrosion initiates, a higher Ni level is beneficial for repassivation.

Nitrogen adds strength and corrosion resistanceNitrogen is a very important addition as it gives a substantial increase in strength and pitting corrosion resistance. At the same time it strongly stabilises the austenite phase. Furthermore, nitrogen improves welding properties.

Molybdenum improves corrosion resistance Molybdenum improves corrosion resistance in most environments, particularly in chloride-containing environments.

Duplex microstructure. Longitudinal cross section of hot rolled plate, light phase austenite, darker (blue) phase ferrite.

The recipe for success: ingredients according to your needs

The mechanical and physical properties are beneficial characteristics of Outokumpu Duplex. The mechanical strength is superior compared to austenitic or ferritic stainless steels, and the physical properties offer new possibilities. This is a clear advantage for structural applications, such as pressure vessels and beam constructions.

pressure vessel approvals

All Outokumpu duplex grades, except for LDX 2101® and LDX 2404™, are listed in EN 10028-7.

Mechanical properties: superior strength

Work is in progress to get a European material approval for LDX 2101®. (LDX 2101®. is partly listed in EN 10088). Work in progress for ASTM/ASME approval of LDX 2404™.

ASME: In ASME II-D 2007 (Metric) edition grades S31803 (2205), S32304 (2304) and S32750 (2507) are listed for general use between -30°C to +325°C. Data for LDX 2101® can be found in ASME code case 2418.

*also available as S31803

Table 1. Chemical composition

Outokumpu steel name

International steel No

Chemical composition, % by weight Typical values

en asTM C n Cr ni Mo others

Du

ple

x

LDX 2101® 1.4162 S32101 0.03 0.22 21.5 1.5 0.3 5mn

2304 1.4362 S32304 0.02 0.10 23 4.8 0.3 –

LDX 2404™ 1.4662 S82441 0.02 0.27 24 3.6 1.6 3mn

2205 1.4462 S32205* 0.02 0.17 22 5.7 3.1 –

2507 1.4410 S32750 0.02 0.27 25 7.0 4.0 –

Au

sten

itic

4307 1.4307 304L 0.02 – 18.1 8.1 – –

4404 1.4404 316L 0.02 – 17.2 10.1 2.1 –

904L 1.4539 n08904 0.01 – 20 25 4.3 1.5Cu

254 SmO® 1.4547 S31254 0.01 0.20 20 18 6.1 Cutable 2 summarises mechanical properties for flat rolled products, (data according to en 10088). the allowed design values may vary between product forms. the appropriate values are given in the relevant specifications/design standards. Grade 4501 is only produced as hot rolled plate by Outokumpu.1) refrs to a80 for gauges less than 3,0 mm

p = hot rolled plate and barH = hot rolled stripC = cold rolled coil and strip, cold drawn bar* mechanical properties according to aStm a240** mechanical properties according to internal

standard am 641.

Table 2. mechanical properties for flat products at room temperature.

Minimum values, according to EN 10088

Outokumpu typical values

p H C p(15mm) H (4mm) C (1mm)

LDX 2101®

proof strength rp0.2 mpa *450 *480 *530 480 570 600

tensile strength rm mpa *650 *680 *700 700 770 800

elongation a5 % *30 *30 *30 38 38 35

Hardness HB 220 230 230

2304

proof strength rp0.2 mpa 400 400 450 450 520 545

tensile strength rm mpa 630 650 650 670 685 745

elongation a5 % 25 20 20 40 35 35

Hardness HB 210 220 225

LDX 2404™

proof strength rp0.2 mpa **480 **550 **550 540 620 640

tensile strength rm mpa **680 **750 **750 750 800 850

elongation a5 % **25 **25 **25/30 1) 33 32 30

Hardness HB max 290 290 290 230

2205

proof strength rp0.2 mpa 460 460 500 510 620 635

tensile strength rm mpa 640 700 700 750 820 835

elongation a5 % 25 25 20 35 35 35

Hardness HB 250 250 250

2507

proof strength rp0.2 mpa 530 530 550 550 590 665

tensile strength rm mpa 730 750 750 820 900 895

elongation a5 % 20 20 20 35 30 33

Hardness HB 250 265 255

14 15

Fig. 1. Curves for reduction of impact toughness to 50% compared to solution annealed condition.

palm oil tank farm, photo courtesy of loders Croklaan

physical properties: new opportunities

easy to weld to carbon steel

Outokumpu Duplex grades have a lower thermal expansion ratio (approximately 13 × 10-6/°C) and higher thermal conductivity than austenitic steels. This means that there are less problems with temperature expansions caused by connecting Outokumpu Duplex with carbon steels. Duplex is a good alternative for lining mild steel vessels that are running with large cyclic temperature variations.

Magnetic properties

Duplex stainless steels are more magnetic than austenitic grades due to higher ferrite content. For safety reasons magnets must not be used to lift duplex sheets.

Table 4. physical properties of duplexstainless steels, according to en 10088.

Physical property 20°C 200°C

Density [g/cm3] 7.8 -

modulus of elasticity [Gpa] 200 186

poisson´s ratio [Dimensionless] 0.3 -

Linear expansion from 20°C to 200°C (x10-6/°C)

- 13.5

thermal conductivity [W/m°C] 15 17

thermal capacity [J/kg°C] 500 560

electric resistivity [μΩ/m] 0.8 0.9

Table 3. impact toughness. minimum values according to en 10028-7 transverse direction.

LDX 2101®* 2304 LDX 2404™* 2205 2507

20°C 60 60 60 60 60

-40°C 27 40 40 40 40

Temperature and embrittlement

Duplex steels are more prone to precipitation of sigma phase, nitrides and carbides than corresponding austenitic steels, causing embrittlement and reduced corrosion resistance. The formation of intermetallic phases such as sigma phase occurs in the temperature range 600-950°C and decomposition of ferrite occurs in the range 350-525°C (475°C embrittlement). Exposures at these temperatures should therefore be avoided. In proper welding and heat treatment the risk of embrittlement is low. However, certain risks exist, for example at heat treatment of thick sections, especially if the cooling rate is low.

Due to the risk of embrittlement, the duplex steels should not be used at temperatures above 250-325°C (See figure 1). The maximum temperature and strength value depends on grade and the design rules being used.

High energy absorption

The combination of high strength and ductility gives Outokumpu Duplex a very good ability to absorb energy. This makes it a perfect material for

applications like blast walls at oil rigs and car body components.

Good fatigue strength in base material

The high tensile strength of Outokumpu Duplex also implies high fatigue strength in the base material. The fatigue strength of the duplex steels follows the proof strength of the material. Our research personnel can provide you with more detailed information, if needed.

What comes to welds, the benefit of the high fatigue strength of the parent or base material is limited. The fatigue strength is reduced by unfavorable weld geometry, residual stresses, distortions and weld defects.

*according to internal specification

16 17

Table 5. shows pre values for different grades. LDX 2101® has a higher pitting and crevice corrosion resistance than 4307. Grade 2304 is on the same level as the conventional molybdenum alloyed steel 4404, while 2205 is on a level with 904L. the duplex grade 2507 has a similar resistance as 254 SmO®.

Corrosion resistance in a wide range of environments

uniform corrosion

The uniform corrosion resistance is generally considered good if the corrosion rate is less than 0.1 mm/year Due to their high chromium content, duplexes offer excellent corrosion resistance in many media, especially in alkaline solutions.

pitting and crevice corrosion: heat exchangers, water heaters, offshore equipment, storage tanks etc.

In chloride solutions LDX 2101® has, in most cases, a better resistance than 4307 and in some cases as good as 4404. Grade 2304 is in most cases equivalent to 4404, while the other more highly alloyed duplex steels show even better resistance. The resistance to pitting and crevice corrosion is often illustrated by the pitting resistance equivalent (PRE) for the material. The most commonly used formula for PRE is:

PRE = %Cr + 3,3x%Mo + 16x%N

The PRE value can be used for a comparison of different stainless steels. A more in-depth way to rank steels is measuring the Critical Pitting corrosion Tem-perature (CPT). Outokumpu uses an electrochemical method, ASTM G150, involving our own developed Avesta Cell, see Fig. 2., and we can provide you with necessary data when requested.

Chloride and sulphide induced stress cracking: boreholes and gas wells etc.

All duplex grades are much more resistant than the standard austenitic grades to chloride induced stress corrosion cracking (SCC). They can thus tolerate higher chloride contents at elevated temperatures.In the presence of hydrogen sulphide and chlorides (e.g. sour conditions in bore holes and gas wells) the risk of stress cracking, at low temperatures, increases.. Such environments can exist, for example, in bore-holes for oil and gas wells. Duplex grades, especially 2205 and 2507, have demonstrated good resistance.

The corrosion resistance of Outokumpu Duplex is generally very good. The resistance is especially good in environments like halide-containing media, oxidising acids, and hot alkaline solutions. This means that for example, heat exchangers, water heaters, offshore equipment, storage tanks, evaporators and flue gas cleaning equipment greatly benefit from the material properties of duplex steels.

Outokumpu steel name PRE

4307 18

LDX 2101® 26

4404 24

2304 26

LDX 2404™ 33

904L 34

2205 35

254 SmO® 43

2507 43

Corrosion fatigue and intergranular corrosion

The combination of high mechanical strength and very good resistance to corrosion gives duplex steels superior corrosion fatigue strength. Due to the duplex microstructure and low carbon content, the duplex grades have a good resistance to intergranular (intercrystalline) corrosion.

erosion corrosion

Stainless steel in general offers good resistance to erosion corrosion. Duplex grades are especially good due to their combination of high surface hardness and good corrosion resistance.

Galvanic corrosion

Galvanic corrosion may occur when two dissimilar metals are electrically connected (as by welding) in an electrolyte. Stainless steel is in most cases nobler than other metallic materials. The most noble metal is protected while the less noble metal is more severely attacked. Stainless steel in contact with carbon steel

rebars in concrete does not cause galvanic corrosion of the carbon steel due to the high pH in concrete. Galvanic corrosion does not occur between different grades of stainless steels as long as both grades are passive.

Atmospheric corrosion

Atmospheric corrosion is not a unique form of cor-rosion, but a collective term to denote the corrosion of surfaces in the atmosphere. When stainless steel is exposed to an aggressive atmosphere it is primarily stained, this is sometimes referred to as tea staining, but it can also be attacked by localised corrosion with time, particularly at high chloride levels as in marine atmospheres. Today there is a duplex grade available for all types of atmospheres.

The Outokumpu Corrosion Handbook

For more information on corrosion and corrosion resistance in different media is plural of medium, please see the Outokumpu Corrosion Handbook. You can obtain your own copy from your local sales office.

Fig. 2. typical critical pitting corrosion tempera-tures (Cpt) in 1m naCl measured according to aStm G150 using the avesta Cell. test surfaces wet ground to 320 mesh. Cpt varies with product form and surface finish.

CPT, °C

span Cpt min. - Cpt max.

100

90

80

70

60

50

40

30

20

0

10

4307 LDX 2101® 4404 2304 4436 LDX 2404™ 2205 904L 2507 254 SmO®

18 19

Fabrication – strong opportunities

Welding

Outokumpu Duplex can be welded with most of the methods used for austenitic stainless steel:• Shielded metal arc welding (SMAW)• Gas tungsten arc welding TIG (GTAW)• Gas metal arc welding MIG (GMAW)• Flux-cored arc welding (FCAW)• Plasma arc welding (PAW)• Submerged arc welding (SAW)• Others: Laser, resistance and high frequency (HF)

welding

In general, the biggest issue with welding Outokumpu Duplex is to maintain the phase balance in the heat affected zone without precipitations. The chemical composition balances the microstructure, and it is important to have the right welding consumable and the right procedure.

Different welding procedure: basic rules

1. weld without preheating2. allow the material to cool between passes,

preferably to below 150°C. For 2507 ≤ 100°C3. duplex filler material is needed and recommended

with the exception for LDX 2101® which may be welded without filler material in some cases

4. the arc energy recommended by Outokumpu should be kept

5. the heat input should be adapted to the steel grade and adjusted to the thickness of the welded material

6. edge preparation angle should be about 10° greater and the land should be somewhat smaller compared to welding standard austenitics

7. if welded with filler, post-weld annealing is not necessary. In cases where heat treatment is considered, e.g. for stress relieving, it should be car-

Outokumpu Duplex offers excellent opportunities to constructing challenging and durable structures. However, due to the high strength of the material, the working process is in some points different than with austenitic or ferritic steels. Outokumpu is here to help you with every possible technical detail. We can provide you with necessary training, computer simulations and further instructions.

Table 6. Characteristic heat treatment temperatures, °C, for duplex stainless steels.

LDX 2101® 2304 LDX 2404™ 2205 2507

Hot forming 1100 - 900 1100 - 900 1120 - 900 1150 - 950 1200 - 1025

Quench annealing 1020 - 1080 950 - 1050 1000 - 1120 1020 - 1100 1040 - 1120

Stress relief annealing 1020 - 1080 950 - 1050 1000 - 1120 1020 - 1100 1040 - 1120

Table 7. Welding consumables.

Steel gradeConsumable

ISO designationTypical composition, % by wt.

C Cr ni Mo n

LDX 2101®

23 7 nL 0.02 23.5 8.0 0.3 0.14

22 9 3 nL 0.02 22.5 8.5 3.0 0.15

2304

23 7 nL 0.02 23.5 8.0 0.3 0.14

22 9 3 nL 0.02 22.5 8.5 3.0 0.15

LDX 2404™

22 9 3 nL 0.02 22.5 8.5 3.0 0.15

2205

22 9 3 nL 0.02 22.5 8.5 3.0 0.15

2507

25 9 4 nL 0.02 25 9.5 3.5 0.25

Welding to other steels including carbon steelsOutokumpu Duplex can be easily welded to other steels including carbon steels. The filler type can be of duplex. When duplex steels are welded to carbon steels an alternative is to use a filler of 23Cr13Ni2Mo type. The risk of galvanic corrosion can be avoided by shielding the joints from moistening. In most cases duplex filler offers more strength and better corrosion resistance. When joining duplex to super austenitic steels, please contact Outokumpu for assistance. Filler metals for joining similar duplex steels, see table 7.

Post fabrication treatmentIn order to restore the stainless steel surface and achieve good corrosion resistance, it is often necessary to perform a post fabrication treatment. Outokumpu Duplex supports all different methods available, such as brushing, blasting, grinding and pickling. Which method to apply depends on what type of imperfec-tions shall be removed, but also on needs to corrosion resistance, hygiene and aesthetics.

The Outokumpu Welding HandbookFor more information on welding and post fabrica-tion treatment, please see the Outokumpu Welding Handbook. You can obtain your own copy from your local sales office.

ried out in accordance with the temperatures stated in Table 6, but with the minimum temperature increased with 30-50°C, to secure full dissolution of intermetallic phase in the weld metal.

8. GTAW and PAW methods: addition of nitrogen (1-2%) in the shielding/purging gas is recommended

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Outokumpu Duplex is available in various shapes and sizes to suit your needs.

• HRP(P), Quarto Plate • CPP(H), coil and plate • CR (C), coil and sheet • Billet, wire rod, bar and rebar• Welded tube, pipe, fittings and threaded fittings• Structural sections, DUPROFTM

• Fasteners and fittings

Our Added value services ease your project and offer ways to save expenses at critical points

• Edge preparation• Cut to shape• Bending• Surface finishing: 2B, 2E, 1D• Polishing• Construction kits• Prefabrication• Modified chemical analysis• Slitted coils• Package solutions• Welding advice• Technical support/Project administration

product assortment and servicesForming

Outokumpu Duplex is suitable for all forming techniques. The higher strength and the lower elongation compared to austenitic stainless steel will however impose some differences in forming behaviour: generally higher force is needed. On the other hand, since duplex design often implies downgauging, the force level can be similar to austenitics. If the forming technique is not already decided, we recommend to choose the most appropriate one for duplex stainless steels.

Machining

The high strength will of course effect the machinability, but not as much as expected. Some information, good to have in mind when machining duplex, is given below:

Stable setupDue to the higher strength the cutting forces will be higher. That will increase the risk of vibrations. The trick is to have a stable setup. Use the shortest possible tool extension good and rigid clamping.

Sharp ToolsUse cutting tools with a positive geometry. The duplex grades are very adaptive to work hardening. A dull geometry will generate a hard surface and decrease the tool life.

Avoid “build up edge”Stainless steels have a tendency to stick to the tool. Problems occur when the cutting speed is too low. The biggest difference between carbon steel and stainless steels when machining is that you face into problems if you are running too slow. The result will be bad surface finish and short tool life. The problem is solved by increasing the cutting speed.

LDX 2101®The lean duplex grade LDX 2101® have superior machinability compared to other duplex grades. Even if you compare with the low alloyed standard austenitic grades LDX 2101®, is easier to machine. For more information on various topics, please contact us.

Things to consider

Cutting, shearing

maximum thickness for shearing and punching is 80-85% of that of austenitic steel

Roll bending more bending force will be needed compared to other stainless steels. through the downgauging, this effect will however be smaller than anticipated. the springback due to the higher strength is large when roll bending.

Break bending

avoid sharp bending radius. minimum ratio between inner radius to sheet thickness should not be less than 2.

Deep drawing

if drawing is dominant, formability is comparable to austenitic stainless steel. if stretching is dominant, formability is closer to ferritic steels.

Roll forming the high strength of the sheet has to be considered in the design of the rolls. if this is made properly there are no problems in roll forming Duplex.

Tooling use Strong, durable tools (hardness, HrC larger than 500, ra-value preferably lower than 0.2 micrometers).

Lubrication Because of the high strength of Outokumpu Duplex and extreme pressure additives are useful in complex forming operations.

Table 8.

Product Type of process route Surface finish

1D Hot rolled, heat treated, pickled. rough and dull. Standard for the most steel types to ensure good corrosion resistance; also common finish for further processing.

2E Cold rolled, heat treated, mechanically descaled followed by pickling.

rough and dull. Light cold rolling can be carried out for thin hot rolled strips.

2B Cold rolled, heat treated, pickled, skin passed or by levelling (as in avesta Works).

Smooth surface with low lustre.

‘2B’ surface finish – perfect for food & health sectorsSurface finish characteristics are not merely a question of appearance. The quality affects to the corrosion resistance as well as cleansability of dirt and bacteria, which is paramount in the food industry and health sector. Outokumpu can additionally offer a ‘2B’

Cane Creek’s World Bicycle relief reserve Headset made out of LDX 2101®.

Table 9.

surface finish in duplex stainless steels, which most often fulfills the industry surface requirements without any further surface treatment – saving both time and money.

See our product programme at www.outokumpu.com/prodprog

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This document is for information only and seeks to provide professionals with the best possible information to enable them to make appropriate choices. Although every effort has been made to ensure the accuracy of the information provided in this document, Outokumpu can not accept any responsibility for any loss, damage or other consequence resulting from the use of this publication. The information provided herein may be subject to alterations without notice.

This document does not constitute a recommendation or a contractual commitment on the part of Outokumpu. Product selection is the responsibility of the specifiers, designers and builders, who are solely responsible for render-ing the finished unit suitable for the use for which it is intended. It is the customer’s sole responsibility to ensure that the product is suitable for the use for which it is intended. Outokumpu shall not provide any guarantee in this respect.

Copyright© Outokumpu Group. All rights reserved.

www.outokumpu.com

Activating Your IdeasOutokumpu is a global leader in stainless steel with the vision to be the undisputed number one. Customers in a wide range of industries use our stainless steel and services worldwide. Being fully recyclable, maintenance-free, as well as very strong and durable material, stainless steel is one of the key building blocks for sustainable future.

What makes Outokumpu special is total customer focus – all the way, from R&D to delivery. You have the idea. We offer world-class stainless steel, technical know-how and support. We activate your ideas.

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