More than 90 years of enhancing stainless steels and solving corrosion challenges



The Outokumpu Corrosion Handbook, published for the first time in 1934, addresses the full scale of corrosion related issues with extensive articles and technical descriptions covering different industrial sectors.

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The Heart of Stainless Steel Competence and Advancement

Not only if you rest, you rust. Corrosion looms over anything that contains steel. While steel-based applications will not encounter severe corrosion-related difficulties inside a regular continental living room, any of these implemented on an off-shore rig, or in a processing unit for chemicals will have to brave a different corrosive environment entirely. Exposure to the elements and contact with corrosive substances gnaw on steel, causing significant damage leading to costs. Any industrial sector therefore has a strong interest in advanced stainless steels to minimize their spending on maintenance work and to ensure their operability.

Within the corrosion lab at the R&D facilities in Avesta, Sweden, Outokumpu is doing complex research to push stainless steels further. The team of metallurgy experts in R&D consult clients from the choice of materials, all the way through construction and operational maintenance. Since an investment in stainless steel always has to make a business case, the corrosion experts find the most efficient materials for each application and each condition the client requires.

Combining research of academic quality with the hands-on work the industry demands, corrosion specialist Björn Helmersson puts research results directly to the test. Through extensive test programs and procedures, where stainless steels are exposed to a variety of highly corrosive solutions, are deliberately activated to test their performance and have to withstand corrosion for long periods of time Helmersson and his team of specialists are able to advance material quality and strength. Through laboratory tests as well as field exposures, the engineers in Avesta have been generating vast resources of experience and research results on corrosion, from which Outokumpu draws when consulting customers and recalibrating materials.

To guarantee state-of-the-art research methods Helmersson visits fairs and conferences for metallurgy and materials. The 28-year old joined Outokumpu as post-grad student in 2014, for his master’s thesis on corrosion in alkaline conditions. By now, Helmersson is presenting his research results from the corrosion lab in Avesta to international audiences of experts proving to future clients the corrosion expertise Outokumpu has been building for their customers for decades.

To channel the results of their extensive research and work on corrosion, Outokumpu’s corrosion experts have been gradually updating their comprehensive manual The Corrosion Handbook over the past 90 years. First published in 1934, and now in its 11th edition, the Corrosion Handbook is testimonial for Outokumpu’s long tradition, expertise and thought leadership on corrosion.

Research & Development: Björn Helmersson at the Corrosion Lab in Avesta, Sweden



The corrosion lab at Outokumpu’s R&D facilities in Avesta, Sweden, is place of work to a team of around 25 engineers. Among a dedicated team of corrosion experts in Avesta, is research engineer and corrosion specialist Björn Helmersson. We spoke to Björn to learn about how he and the team of specialists approach corrosion.

1. We all have complained about “rust” before. But what is corrosion really?
Corrosion is a natural process. It is a gradual decay of materials, through reaction with their environment. For metals, this is driven by their desire to return to their more stable mineral state. This usually means the electrochemical oxidation of the metal in reaction with an oxidant. Lots of steel-based applications corrode just from wear and tear and atmospheric corrosion – that’s pretty much being left out in the rain. But there are other substances that affect the process. Aggressive chemicals for example. In the case of Outokumpu, the material is stainless steel, which in many ways is different from carbon steel.

2. What is so special about stainless steel?
The key to the corrosion resistance of stainless steel is the addition of chromium to the alloy. This allows the material to form a very thin chromium rich film that is resistant to a wide range of media. We say that the material is passivating. This means that the corrosion rate is negligible as long as this passive film is stable. Carbon steels, on the other hand, will always corrode to some extent – the question is just how quickly. By adding even more chromium and other alloying elements, the corrosion resistance – as well as other properties – can be improved even further.

3. What industries have to deal with corrosion on a day to day basis?
Corrosion looms over anything that contains steel, regardless of industry. Steel-based applications will not have a hard time inside a regular living room. But any of these implemented on an off-shore rig, or in a processing unit for chemicals will have to brave a different corrosive environment entirely.

4. What are the consequences of this ever-present corrosion for the industries?
Exposure to the elements and contact with corrosive substances gnaw on steel. That causes significant damage and leads to costs. Therefore, any industrial sector has an interest in high quality stainless steel. It helps minimizing their spending on maintenance work and to ensure their operability.

5. How do you work here in Avesta – do you have actual products?
Within the corrosion lab, we are doing research to push stainless steels further. We test, we try things out, we fail, we try again until we succeed, and it works exactly how our client needs it to. And yes, we develop products and have done so for many years.

In Avesta, we developed the well-established high-alloyed austenitic stainless steel Ultra 254 SMO with extremely high resistance to both uniform and localized corrosion. This product was developed especially for oil and gas offshore platforms and the pulp and paper industry, where corrosive environments are normal. If you’re looking for a grade that has proven itself in the oil and gas industry with excellent corrosion resistance - that’s your steel. We’ve also developed the grade Ultra 654 SMO. It’s based on Ultra 254 SMO but we pushed it further in all aspects. It’s currently the most corrosion-resistant stainless steel in the world. It’s a very high molybdenum and nitrogen alloyed austenitic product with high mechanical strength. Ultra 654 SMO can in many cases compete with more expensive nickel-based alloys in terms of wet-corrosion resistance.

What we’ve only recently developed is the Forta EDX 2304. That’s the Forta DX 2304, but enhanced, with a slightly modified alloying composition, mainly to improve corrosion resistance. It has good resistance to localized and uniform corrosion, as well as stress corrosion cracking. And also a high mechanical strength. Despite the enhancement, the Forta EDX 2304 fits within the same standards, but with improved performance.

In product development, it becomes increasingly important, to make leaner alloys. Lean means, that we try to reduce the percentage of expensive alloying elements and of alloying elements with high price-volatility, such as nickel. We have done this with Forta FDX 27, the most recent grade we developed in Avesta. Our grade Forta LDX 2101 was one of the pioneering grades in terms of lean alloying in duplex grades.

6. Do you offer your clients some sort of condensed guidelines? General stainless steel guidelines, if you will?
Yes, we offer several handbooks. The Corrosion Handbook is one of Outokumpu’s handbooks. There are also others, such as the Handbook of Stainless Steel and the Welding Handbook. The Corrosion Handbook is a comprehensive manual on – as the name suggests corrosion. To channel the results of extensive research and work on corrosion. Outokumpu has been updating and publishing it gradually over the past 84 years. First published in 1934, and now in its 11th edition, the Corrosion Handbook is a testimonial for Outokumpu’s long tradition, expertise and thought leadership on corrosion. Both the Handbook of Stainless Steel and the Welding Handbook respectively, illustrate Outokumpu’s expertise in their other core businesses.

 

Research & Development: The Advantages of Choosing Duplex Stainless Steels in Bridge Construction

Bridges are built to be left out in the cold, wind and rain. To be trampled on by pedestrians and crushed by car tires. The strain put on them is enormous and the resulting cost for keeping them functioning significant. But even with meticulous care and maintenance, a bridge’s lifecycle usually ends sooner rather than later.

To extend bridge lifespan, the structural use of Duplex stainless steels has increased significantly in the last twenty years. Their product properties offer high strength, good corrosion resistance, very low maintenance requirements and hence low lifecycle costs. The initial investment required for a stainless bridge is higher than for conventional construction materials but, after approximately 30 years, when carbon-steel bridges have to be repainted and wooden bridges replaced, stainless steel starts to pay off. As a business case, a long lifespan is key for a bridge project and, over a reference period of approximately 120 years, stainless steel beats the costs of wooden bridges and steel bridges by a substantial margin.

However, to maximize the materials’ full potential and find the balance between quality and cost efficiency, initial selection of the right material grade is also key. It depends heavily on climatic conditions on-site, the specific requirements of each operational scenario, bridge design and many other factors. Due to its extensive material research and development capabilities and more than a decade of experience in infrastructure projects, Outokumpu is able to support its clients by evaluating these fundamental conditions to determine the right material selection for each construction scenario.

To maintain and further this competence, Outokumpu conducts complex research and develops stainless steels of the highest quality at its R&D centers in Avesta (Sweden), Krefeld (Germany) and Tornio (Finland). Taking advantage of its extensive R&D facilities, Outokumpu offers customer consultation to assist in the process of identifying the ideal materials for individual construction projects. On the basis of this high-quality research, Outokumpu conducted a study on the usage of Duplex stainless steel in bridge construction in 2015. Together with engineering consultancy Arup, they investigated its performance on seven bridges in regions ranging from the cold, wet areas of Sweden to the Mediterranean heat of Menorca. The study verified the high importance of initial material selection based on climate conditions in order to achieve the best results in long-term corrosion resistance.

The following examples illustrate the differences:

Outokumpu recently supplied Duplex stainless steel for two bridge projects in Sweden. They both consist largely of the lightweight structural steel Lean Duplex Forta LDX 2101. The light yet robust product is ideal for the demanding Nordic conditions but does not rely on costly and price-volatile materials like nickel. Spanning a quiet sea inlet and not having to support car traffic, Forta LDX 2101 was chosen over the more corrosion-resistant Forta DX 2205 alloy. Being a lean-alloyed Duplex product with good resistance to localized and uniform corrosion, as well as stress-corrosion cracking, Forta LDX 2101 is also an excellent alternative to coated carbon steel in structural components, guaranteeing a much longer lifecycle.

If the bridge’s environment has a very high risk of chloride content (<0.25 km from the sea) and a dryer climate with little rain washing, there is a more immediate danger of corrosion. A research study on Duplex stainless steel in bridge-construction conducted in 2015 by Outokumpu and engineering consultancy Arup analyzed the performance of Outokumpu Duplex stainless steel. Built in 2005, the Road Bridge in Cala Galdana, Menorca, Spain, replaced an existing concrete bridge that was only 30 years old but exhibited significant degradation due to the corrosive marine environment. The pedestrian bridge in coastal Zumaia, Spain, is exposed to similar maritime conditions. The bridges use Forta DX 2205 for arches, balustrades and bridge-beam. This grade offers very good resistance to uniform and localized corrosion and stress corrosion cracking and, the study found out, works very well in the bridges’ highly corrosive surroundings. The only exception was discoloration on the surface, which was owed to external contamination, most likely through contact with a carbon steel fence and carbonate washing out of the concrete bridge deck. Both contaminations are superficial and usually easily removed with dilute acid-based cleaners.

The study also analyzed the performance of Outokumpu Duplex stainless steel in the Celtic Gateway Bridge in Holyhead, Wales. Of course, the notorious British weather asks its own questions of construction materials. After nine years, the arch surfaces and detailing were in generally good condition. Some lime was deposited and appeared to be from water run-off from the concrete deck onto stainless steel’s surfaces. This was not causing any damage to the material. The bridge is adjacent to an ocean harbor, so it should be in immediate danger of corrosion due to salt exposure. However, the harbor below the bridge is well sheltered and wave conditions usually calm. There is no high-speed water traffic passing under the bridge to cause splashing seawater. That is why Outokumpu chose Forta DX 2304 for the construction of the bridge. Forta DX 2304 is a Duplex product with a leaner alloying composition than Forta DX 2205 and less price-volatile elements. It has a somewhat lower resistance to localized and uniform corrosion compared to Forta DX 2205, but the steel grades are similar with respect to other characteristic properties such as stress corrosion cracking resistance and high mechanical strength. Its particularly smooth surface finish improves corrosion resistance of the stainless steel used in its construction, making it an ideal choice for the specific surroundings in Holyhead.

Selected Outokumpu bridge-projects: A variety of Forta duplex steel grades to withstand different corrosive environments

 

Steel
Grade

Bridge Name
(Location)

Year

DSS*
Elements

CRC*

Level of risk
exposure to

Exposed
Conditions

Estimated
C-Class*

          CI-*
SO2*
   

Forta
LDX
2101

Orrhammarvägen
Road Bridge
(Flen, Sweden)
2009

Brige
beam,
bearing plate

II
L
L
Sheltered
C2
Forta
LDX
2101

Añorga Railways
Bridge
(San Sebastian,
Spain)

2011

Arch,
beam

II/III M L Open/Sheltered C3
Forta
LDX
2101

Road Bridge
(Nynäsham,
Sweden)
2011

Bridge
beam,
Abutement
plate

IV V L Sheltered C3
Forta DX
2304

Puerto Arrupe
Pedestrian Bridge
(Bilbao, Spain)
2003

Box girder

 II/III M L Open/Sheltered C3
Forta DX
2304

Celtic Gateway
pedestrian Bridge
(Holyhead, UK)
2006
Arch
III/IV V L Open/Sheltered C3
Forta DX
2205

Pedestrian Bridge
(Zumaia, Spain)
2008 Bridge
beam,
balustrade
 III/IV H L Open/Sheltered C4
Forta DX
2205

Cala Galdana
Road Bridge
(Menorca, Spain)
2005 Arch, deck,
balustrade
 IV/V V L Open/Sheltered C5

*DSS: Duplex Stainless Steel
*CRC: Corrosion Resistance Class according to design standard EN 1993-1-4 Annex A
*Risk exposure to chloride (Cl-) and Sulfur (SO2) where L = Low, M = Medium, H = High, V = Very high
*Estimated C-Class in accordance with ISO 9223, ranging from C1 (lowest) to CX (most corrosive class)


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Jun 28, 2019