There are a number of Gulf infrastructure projects in the past few years that have chosen Duplex stainless steel over carbon steel. The three major MSF/MED desalination plants in the Gulf region, namely Taweelah B (Abu Dhabi), Jebel Ali L2 (Dubai), and Ras Abu Fontas B2 (Qatar), have all preferred Duplex 2205 in critical evaporator components. In this article we will see duplex vs. carbon steel in UAE and other Gulf countries and why there is an upward trend of choosing Duplex steel over carbon steel. It will cover strength-to-weight ratio, lifecycle cost savings, and coastal project materials.
What are the major constituents of Gulf infrastructure projects?
The Gulf Cooperation Council (GCC) consists of the countries UAE, Saudi Arabia, Qatar, Oman, Kuwait, and Bahrain. These nations are focusing on expanding their infrastructure on a very large scale. In fact, it is one of the biggest expansions in the world. The Vision 2030 is Saudi Arabia’s strategic blueprint, which aims to transform the economy, society, and governance of the region by the year 2030. These projects require metals and alloys that have a high strength-to-weight ratio, better lifecycle cost savings, and support coastal project materials.
The major areas of infrastructure that they are looking to change are
- Transform transportation through the development of better roads, railway stations, and railway lines, as well as ports and airports.
- Develop urban areas through the creation of smart cities and housing.
- Empower various Energy areas like oil, gas, and other renewable energy sources.
- Manage water and environment better through desalination, sewage, drainage projects
- Creation of different kinds of industrial zones as well as logistics and manufacturing hubs.
Why are the conditions of the Gulf infrastructure projects harsh?
- Intense Temperature
The heat in the Gulf countries is very high because of the desert conditions and the hot sun. The temperatures can even surpass temperatures of 50°C. This extreme temperature leads to constant expansion and contraction of joints, bolts, and seals in buildings, pipelines, and even bridges because of the thermal intensity.
- Excessive humidity and Condensation
The moisture content in these countries is also very high. The humidity content can occasionally even exceed 80% in some coastal towns such as Dubai, Doha, and Muscat.
- High chloride and saline percentage
The infrastructure constantly faces challenges because of the saline atmosphere and salt water, which are common in the coastal and offshore regions of the UAE, KSA and Qatar. This is a particularly serious case for traditional stainless steels.
- Regions with seismic activity
There are several areas with mildly seismic regions in Oman, the UAE, and the KSA that border Iran, which require alloys that have a high strength-to-weight ratio.
- Dependence on desalinated seawater
The Gulf countries depend extensively on desalination facilities. These facilities come with the drawback that the materials and infrastructure are exposed to harsh chemicals, high temperatures, and chlorides, which opens the necessity of alloys and metals with an excellent strength-to-weight ratio and better lifecycle cost savings.
- Dust pressures and loads from wind
The substantial loads of storms also affect the infrastructure and the entire process of infrastructure development. Therefore, there is a necessity for metals and alloys that can shield the structures and stabilize them during such events. They need to have a good strength-to-weight ratio, lifecycle cost savings, and enhanced coastal project materials.
What is Duplex Steel?
Duplex steel is a kind of stainless steel with a unique dual-phase microstructure. This structure has approximately an equal quantity of austenite and ferrite. This mixture is highly efficient and has the following mechanical and chemical compositions.
Chemical Composition of Duplex Grade
| Element | Composition (%) |
| Chromium (Cr) | 21.0 – 23.0 |
| Nickel (Ni) | 4.5 – 6.5 |
| Molybdenum (Mo) | 2.5 – 3.5 |
| Nitrogen (N) | 0.14 – 0.20 |
| Manganese (Mn) | ≤ 2.0 |
| Silicon (Si) | ≤ 1.0 |
| Carbon (C) | ≤ 0.03 |
| Phosphorus (P) | ≤ 0.03 |
| Sulfur (S) | ≤ 0.02 |
| Iron (Fe) | Balance |
Mechanical Properties of Duplex Steel
| Property | Value |
| Tensile Strength | ≥ 620 MPa |
| Yield Strength (0.2%) | ≥ 450 MPa |
| Elongation | ≥ 25% |
| Modulus of Elasticity | ~ 200 GPa |
| Hardness (Brinell) | ≤ 293 HB |
| Impact Resistance | Excellent (even at -50°C) |
| Density | 7.80 g/cm³ |
What are the categories of Duplex Steel?
The category of Duplex stainless steels is categorized into several grades. Pitting Resistance Equivalent Number (PREN) is the measurement parameter. All these steels have the properties of a good strength-to-weight ratio, lifecycle cost savings and supporting the coastal project materials. These grades are as follows:
- Lean Duplex Grades (PREN 22–27)
- S32101 (LDX 2101)
- S32202
- S32304 (2304)
- Standard Duplex Grades (PREN 28–38)
- S31803 / S32205 (Duplex 2205)
- Super Duplex Grades (PREN 38–45)
- S32750 (2507)
- S32760 (Zeron 100)
- Hyper Duplex Grades (PREN > 45)
- S32707
- S33207
What is Carbon steel?
Carbon steel is a type of metal alloy in which the percentage of carbon ranges from 0.05% to 2.1% by weight. They do not have a good strength-to-weight ratio. Even though they are cheap, their lifecycle cost savings are very low, and they do not have a complete ability to assist the coastal project materials in the conditions of Gulf countries.
Chemical Composition of Carbon Steel
| Type | Carbon Content (%) | Manganese (%) | Other Elements |
| Low Carbon Steel (Mild Steel) | 0.05–0.30 | 0.30–0.90 | Small amounts of Si, P, S |
| Medium Carbon Steel | 0.30–0.60 | 0.60–1.65 | Traces of S, P |
| High Carbon Steel | 0.60–1.00 | 0.30–0.90 | May include Cr or V for hardness |
| Ultra High Carbon Steel | 1.00–2.00 | Variable | Limited use – tool steels |
What are the other minor elements in carbon steel?
- Silicon (Si): 0.10–0.30%
- Phosphorus (P): ≤ 0.04%
- Sulfur (S): ≤ 0.05%
Mechanical Properties of Carbon Steel
| Grade | Yield Strength (MPa) | Tensile Strength (MPa) | Elongation (%) | Hardness (HB) |
| Low Carbon Steel (A36) | 250 | 400–550 | ≥ 20 | 120–160 |
| Medium Carbon Steel (1045) | 310–580 | 565–725 | 12–18 | 170–210 |
| High Carbon Steel (1095) | 500–800 | 800–1000 | 10–15 | 200–250 |
| Ultrahigh Carbon Steel | >800 | >1000 | <10 | >250 |
Duplex vs. carbon steel in UAE – Which is better?
1. Duplex vs carbon steel in the UAE based on corrosion resistance
Duplex Stainless Steel, like Grade 2205, can resist chloride-induced corrosion in a better manner than carbon steel. It shields against various corrosive elements:
- Pitting
- Crevice corrosion
- Stress corrosion cracking
Therefore, it can provide complete support for coastal project materials.
2. Duplex vs carbon steel in UAE based on coating requirements
The coastal and offshore environments of various areas of Gulf countries consist of a high percentage of salt in the air. Moreover, there is also seawater, which has extreme salinity. These aspects can degrade carbon steel if it is not coated heavily, and they can make the structures vulnerable to corrosion. Duplex stainless steel does not require any such coating to assist in letting the coastal project materials thrive well.
3. Duplex vs Carbon Steel in UAE considering Strength-to-Weight Ratio
Duplex stainless steel is better than carbon steel because its yield strength is almost twice that of carbon steel. This yield strength helps designers to utilize thinner sections and structures that can be lighter. Even though the sections are thinner and lighter, it can still maintain the required strength in different kinds of
- Bridges
- High-rise buildings
- Pressure vessels
4. Lower Cost because of durability
The Duplex Stainless steel is comparatively more expensive than carbon steel initially. However, the service timeframe of Duplex steel is much longer than carbon steel. Moreover, the maintenance cost is also lower, and the replacement chances are also few. These charecteristic makes Duplex steel a cost-effective alternative over a long period of time.
Therefore, Duplex steel is an Ideal option for projects with a lifespan of more than 40 to 50 years, like
- Desalination plants
- Oil & gas pipelines
- Seawater cooling systems
5. Resistance to Gulf-Specific Environments
As discussed earlier, the conditions of Gulf countries are very unforgiving, especially
- High humidity
- Salt spray
- High temperatures
- Sand abrasion
Carbon steel cannot withstand the above circumstances as well as Duplex steel and requires a very costly protective system to protect the infrastructure.
Conclusion
When you see duplex vs. carbon steel in UAE. Duplex Steel has an extended level of service capability, which means that their lifecycle cost savings is high. It also reduces the chances of the frequency of replacement. Another major factor of its acceptance is that it displays a high strength-to-weight ratio, which optimizes the material well. It also exhibits efficiency in saving a lot of energy through better performance at extreme temperatures. Moreover, it has the property of getting recycled, which is why it has become a hot favorite in the infrastructure projects of gulf properties because of its support to non-coastal and coastal project materials.