Attività

Stainless steel has unique properties which can be taken advantage of in a wide variety of applications in the construction industry. This paper reviews how research activities over the last 20 years have impacted the use of stainless steel in construction. Significant technological advances in materials processing have led to the development of duplex stainless steel pipe with excellent mechanical properties; important progress has also been made in the improvement of surface finishes for architectural applications Structural research programmes across the world have laid the ground for the development of national and international specifications, codes and standards spanning both the design, fabrication and erection processes. Recommendations are made on research activities aimed at overcoming obstacles to the wider use of stainless steel in construction. New opportunities for stainless steel arising from the shift towards sustainable development are reviewed, including its use in nuclear containment structures, thin-walled cladding and composite floor systems.

Stainless steel has many desirable characteristics which can be exploited in a wide range of construction applications. It is corrosion-resistant and long-lasting, making thinner and more durable structures possible. It presents architects with many possibilities of shape, colour and form, whilst at the same time being tough, hygienic, adaptable and recyclable.

The annual consumption of stainless steel has increased at a compound growth rate of 5% over the last 20 years, surpassing the growth rate of other materials. The rate of growth of stainless steel used in construction has been even faster, not least due to rapid development in China. It is estimated that in 2006, approximately 4 million tones of stainless steel went into construction applications worldwide, 14% of the total quantity consumed. 

Stainless steel has traditionally been used for facades and roofing since the 1920s. There are also early examples of it being used structurally, for example in 1925 a reinforcing chain was installed to stabilize the dome of St Paul’s Cathedral, London. Nowadays, stainless steel is used in a very wide range of structural and architectural elements, from small but intricate glazing castings to load-bearing girders and arches in bridges.

The corrosion resistance of duplex grade 1.4362 is similar to that of 1.4401. The more highly alloyed 1.4462 displays superior corrosion resistance, especially to stress corrosion cracking. High nickel prices have more recently led to a demand for lean duplexes with low nickel content, such as grade 1.4162 shown in the table. The corrosion resistance of grade 1.4162 lies between that of 1.4301 and 1.4401; it currently costs slightly less than grade 1.4301.

Although usually used internally in buildings, some ferritic grades have been developed which are suitable for building envelope and structural products. For example, over the last 10 years, grade 1.4510 has been used widely in France in a tin-coated roofing system. This tin-coated finish weathers over time, gradually developing into a matt-grey patina.

Over the last 20 years, significant developments have occurred in materials processing and finishing technology, often driven by exacting architectural requirements for specific projects. The range in surface finishes has extended, ranging from matt to shiny, smooth to very rough, with combinations possible by juxtaposing finishes, adding colour etc. More finishes have become available—involving metallic and organic coatings, electrolytic and PVD (Physical Vapour Deposition) coating processes or skin passing operations. They have improved the competitive position of stainless steel compared to other high volume metallic roofing materials such as zinc, aluminium, copper and even carbon steel. The performance of the stainless finishes has also been improved in order to meet strict hygiene and cleaning requirements. Improved manufacturing processes have resulted in greater consistency of surface finish, both across a sheet and from batch to batch. Products are also now able to meet tighter dimensional tolerances.

Traditionally stainless steel welded tubes were produced by tungsten inert gas (TIG) welding. However, with the advent of reliable, high-power laser power sources, the laser beam welding (LBW) process has moved quickly into the production of stainless steel longitudinally welded tubes. The energy concentration reached in the focused spot of a laser beam is very intense and is capable of producing deep penetration welds in thick section stainless steel, with minimal component distortion. The process originally employed high capital cost equipment and its use was reserved for mass production manufacturing. However, now that more compact equipment has been developed, the use of laser welding is becoming more widespread. In addition to hollow sections, laser welded stainless steel I sections, angles and other shapes are now available (Fig. 2).