Aluminium, being a light material (three times lighter than steel), is ideal for specific applications. In paper technologies, large amounts of extremely moist, steam-filled exhaust air is extracted through tightly welded, low-pressure duct systems. With regard to corrosion, AlMg3 is comparable to stainless steel for this type of application. However, being lighter it is less expensive and is a great advantage in respect to the supports and loads that the structure must already bear.

Carbon steel can also be used for high temperatures, for example, S235JR for temperatures of up to 300°C. Heat resistant steels were developed for use in high temperatures, including 16Mo3 which, on account of its chemical composition, can be used for temperatures of up to 450°C. In contrast to stainless steel, it is more susceptible to corrosion; however, the purchase price is considerably lower. In the project pictured here, the section used for lifting the pipe is undergoing a complete dye penetrant inspection.

International projects are often bid for using materials produced according to the ASME-code. These generally conform to European standards and can be given both American and European stamps of approval. Both standards are verified in the material certificate and the material is also stamped with both labels at the factory. Typical ASME-stainless steel materials are 304L, 316L and 321 – LBF is experienced and has the proper credentials in matters of purchasing, documenting, and processing.

A material not only needs to function well, sometimes aesthetic reasons can also be decisive for using certain materials. Pre-ground stainless steel sheet material can be used. The pre-processed surface area is protected by a factory-applied foil suitable for lasers.  In this project for exhaust air towers, the ground sheet metal is rounded and bolted together from the inside; welds are found only on the base plate and the tower head.

At operating temperatures above 400 °C, it is necessary to test which stainless steel can be used, taking into account both the components of the media and the operating conditions. 1.4541 or 1.4571 can be considered up to temperatures of approximately 500°C, e.g. during continuous operation and with a dry medium. Alternatively, 1.4828 and 1.4841 can be used (these are high temperature stainless steels that can be used for temperatures reaching up to approx. 800° – 900°C). Such temperatures occur for example in engine test stands or in furnace technologies.

Stainless steel 1.4541 is used in exhaust gas lines and stacks discharging furnace exhaust air with maximum temperatures of approx. 450° - 500°C. Depending on the type of fuel, exhaust gases contain among other things sulphur dioxide or nitrogen oxides (SO2 or NOX), which in water form sulphuric acid or nitric acid. Particularly facilities that are not in continuous operation are at risk of this, for example, through the build up of condensation. During the design process, the demands that the temperature place on the material must be considered as well as the protection needed to prevent corrosion.