Using Duplex steel has some advantages, which are essential in a few industries. One of them is definitely the shipping industry with the transport of corrosive respectively cryogen fluids. The high mechanical values, combined with the high corrosion resistance of duplex grades, allow significant weight savings, which are not only important for the resourcing market.
Tanks for shipping industry
Due to the globalizing, more and more goods are being transported by vessel over sea. These goods are for instance raw oil and oil products, chemicals, liquid gases, acid sulphur, phosphoric acid, fish oil, lubricants, methanol, edible oils, biodiesel, acetic acid but also honey, orange juice, flour or wine and many more.
Dependent on the loading, specific buildup forms and equipment have to be constructed. Some loads, in example liquefied natural gas (LNG) has to be transported at very low temperatures, around – 164 degrees Celsius. On the other hand, melted bitumen has to be transported at very high temperatures around 250 degrees Celsius in separate tanks, which are supported by special processes.
The choice of material for the high variety of applications depends on many factors:
- Weight savings, to increase the load capacity, for example for vats, fire protection walls, pipelines, pumps as well as construction parts made from sheets or structural profiles
- Construction costs (the thinner the wall thicknesses, the cheaper are transportation or welding costs)
- Maintenance costs (Life Cycle Costs); these are calculated for a usage duration of max. 50 years
- Corrosion resistance against different fluids
- Future-oriented material choice as it is obvious, that more and more corrosive products are transported, which result in introduction and compliance of stricter environmental constraints
Duplex Stainless Steel for the Shipping Industry
Also, more Duplex grades in the shipping industry are used. The reasons therefore are:
- Very good corrosion resistance against many liquids/media
- High strengths, which make it possible for the construction engineers to use thinner wall thicknesses and structural profiles and which have a reduced charge weight as a positive consequence. Using Duplex for storage tanks, a weight reduction for some construction components of up to 40% in comparison to conventional austenite can be achieved
- Customized special profiles can be manufactured project-specific
- Good welding characteristics
In many cases, it is necessary – due to security and environmental protection reasons – double -walled transportation containers have to be used. For these particular containers, often it is essential to use special profiles in duplex, as standard profiles in austenitic grades do not fulfil the asked requirements in terms of corrosion resistance and strengths. Special profiles – as the name already indicates it – have the great advantage that they can be produced project specifically as well as customized and can be delivered just in time.
Due to the fact that almost all above mentioned fluids have to be stored temporarily, high requirements are also demanded for the storage tanks. The advantages of Duplex grades have been mentioned already before.
In this regard, it is also possible, at least partially, to substitute tanks, made of commercial grades, by those, made of Duplex grades. Reasons for that are on the one hand the life cycle costs (construction, transportation, welding, maintenance costs etc.) and on the other hand certainly the great potential to save weight.
In this segment, all standard product shapes are needed for the fabrication. However, without doubt, there is also the demand for special profiles, as these tanks are not standardized but more a custom-made products, which are specially designed for each project.
Tanks, containers, pressure vessels and trestles for the oil and gas industry
Duplex steels have been used in the oil and gas industry since around 35 years.
It has started with the use of 1.4462/UNS S32205 according to ASTM/ASME (ASTM A240, ASTM A789/A790, ASTM A928). In the meantime, also Lean Duplex, Super Duplex and Hyper Duplex grades are utilized depending on the requirements regarding corrosion resistance and needed tensile strength.
In addition to the earlier mentioned reasons to use Duplex steels, two other significant characteristics can be seen positively for the oil and gas industry:
- Extraordinary resistance in comparison to austenitic grades against corrosive media such as carbon dioxide, hydrogen sulphide, chlorides and media with low ph-value
- Extraordinary resistance in comparison to austenitic grades against stress corrosion cracking in media with high chloride content
Again, the focus lies in the first place in reducing the life cycle costs and not the material costs for the several parts. The properties of the used materials are essential as high costs can be generated should production downtimes occur, especially in the oil and gas industry.
For the time being one can assume that also in near future Duplex grades will remain first choice in above-mentioned industries. Furthermore, it is likely that most of the producers of Duplex steel are going to further develop and improve the different grades, that they will also be able to supply material that meets new challenges in future.