Weathering steel is a low carbon steel family that has additional alloying components combined in with the atoms of carbon and iron. These alloying components give weathering steel higher strength and more corrosion resistance than standard low carbon steel grades. As a result, weathering steel is generally utilized in exterior applications or in conditions where normal steel would be prone to rust.
Weathering steel is a specialty steel that produces patina (rust layer) when it comes in contact with the atmosphere for a specific time. Additionally, it needs alternating wet and dry cycles to create a patina coating on weathering steel. In addition, layer generation depends on the area, environmental conditions and many other elements. Thus, it is usually produced in the unpainted form which has a 120-year life span.
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Types of Weathering Steels
On the basis of type, the weathering steel is segmented as follows
- Corten-A: Corten A is a weatherproof steel that is made up of alloying copper, chromium and nickel. Moreover, Corten A has incorporated phosphorus to ensure that it is the perfect material to use in the gas flue and esthetic facias Corten A is not recommended in heavy load applications.
- Corten-B: Corten B type is the one that is preferred as it is much stronger and tougher to be used in structural application. The primary weathering steel use is in building and construction especially in bridge construction. Within the past decades, weathering steel has become an important material used in the construction of bridges. This is because of low maintenance that comes with use of weathering steel, better corrosion resistance, and the longer shelf life of the structure.
Advantages of Weathering Steels
- Very Low Maintenance: Weathering steel structures only need to be periodically inspected and cleaned to be functional. This is why it is ideal to be used in structures that are hard or unsafe to access (like bridges), and reduce future inconveniences.
- Initial Cost Benefit: The cost of the steel material can be compensated by the removal of the necessity of having the protective paint system. Indicatively, in bridges that use a HA Type 2 paint system the cost of weathering steel has been indicated to be nearly 5 percent less than alternative painted steel.
- Whole-Life Cost Benefits: Not only the direct costs of maintenance operations are significantly reduced because of the reduced maintenance requirements, but indirect costs, such as traffic delays or rail closures, are also reduced.
- Quickness of Construction: With the elimination of the shop painting and on-site painting, the time of construction as a whole is shortened considerably.
- Broad Applications: As it is not easily rusted in the atmosphere, weathering steel is applicable to numerous structural and architectural projects without being painted; such as open-frame buildings, transmission towers, sculptures, and bridges. It is also a good ducting material, chimney and flues due to its high temperature tolerance.
- Good Appearance: Mature weathering steel forms a beautiful natural appearance which may in most cases blend with its environment. It has a subtle change in appearance and becomes better as it ages.
- Weathering Steels Advantages: Weathering steels have the ability to lower the quantity of oxidizing steel above 400 o C (752 o F). Even in the absence of water at such temperatures, a patina will develop. Although the precise performance enhancement varies with the heating cycle and environment, a typical gain is an increase in temperature tolerance of about 50 0 C (90 0 F) over carbon manganese steels with the same loss of the material.
- Environmental Benefits: There will be no future maintenance activity, which will avoid problems related to volatile organic compounds (VOCs) of paint and the necessity to clear abrasive blast-cleaning wastes.
- Safety Benefits: Safety hazards associated with the first painting are eliminated and the risks of the future work associated with maintenance are minimized.
Weathering Steel Grades
Weathering steel is a low-carbon steel alloy that is made of different grades. These grades consist of proprietary grades like CORTEN A and CORTEN B and others are patented grades like Patinax. A large number of these proprietary and patented specifications are related to the existing ASTM categories such as A 242 and A 588.
Uses of Weathering Steel
The use of weathering steel in exposed structural work is very common since it greatly lasts longer than plain carbon steel in the outside world. This strength does not require frequent repaint and recoating, and so it is very convenient with large structures. Typical uses are in building design and constructing bridges. The coating of rust or patina is actually a protective covering that will slow down the rate of corrosion to such a degree that the structural life expectancy is frequently dictated by other causes way before corrosion can be a cause of concern.
Weathering Steel Availability
The application of weathering steel usually varies with the painted and unpainted which is determined by the exposure of the structure to the environment.
Painted Weathering Steel
Weathering steel needs painting and maintenance when the structure will be regularly wet because the protective patina layer needed will not develop well when the structure is always wet.
Example: Any area where the bottom of a structure is in touch with the ground, partly submerged in water, buried in soil or overgrown with dense vegetation needs to be painted.
The paint system is expected to be above the water, soil or vegetation in order to cover the entire steel in the constantly wet area.
Unpainted Weathered Steel
The most common one is unpainted weathering steel, which is used in the environments where the steel is not in constant contact with water.
Common Applications: This is most likely to be used on railway bridges, shipping containers, and sculptures where the steel is periodically dry, and the patina of stability is allowed to develop and cover the surface.
Pre-weathered Alternative: Other manufacturers provide so-called pre-weathered weathering steel, which is a form of untainted steel that has undergone a chemical treatment to attain the preferred initial rusted look at a quicker pace.
