Steel is an alloy which due to its qualities is useful in many industrial sectors. Its resistance, combined with its machinability and toughness, has made previously unimaginable constructions and applications possible. Over time, new industrial needs have led to the development of various steel alloys. An example in this sense is that of the steels used for making pressure vessels: these products, in fact, are subjected to in-depth checks and must comply, also in terms of the materials used, with certain technical specifications in order to be considered safe. These containers indeed have one characteristic: the internal pressure is different from the atmospheric pressure. The material therefore, with which they are made, must support this difference guaranteeing the non-deformable nature and integrity of its structure.
The steels most used for making furnaces, pressure vessels, boilers and heat exchangers are carbon steels and stainless steels, such as, for example, SA516.70 and A516.70.
These alloys have remarkable toughness and weldability characteristics and meet all the standards necessary for applications in the petrochemical, pharmaceutical, food and oil & gas industries, which need to transport or store liquids and gases under pressure.
Alloyed carbon steels have a high resistance to corrosion and impact and tensile strength (essential for the production of tanks destined for specific industrial sectors). The use of particular alloys depends on the destination of the pressure vessels and the substances with which they will enter into contact internally and externally.
Stainless steels offer a good relationship between corrosion resistance and minimum thicknesses required. These steels are preferred in particular for making pressure tanks that are intended for external installation and, therefore, often subject to the action of atmospheric agents, which over time would corrode the external surface of tanks built with other materials.
The best steels to use in pressure tanks and heat exchangers have a chemical composition with a high amount of manganese and a good amount of silicon: these two alloying elements are known for their deoxidizing properties and for improving the hardenability of the alloy in which they are found.
In addition, steels with a high nickel content are preferred for managing liquefied natural gas, or copper, for tanks in contact with salt water.
The SA516.70 and A516.7 steels used for the construction of pressure vessels must be of controlled and certified origin. The selection of the material used for their construction is in fact one of the requirements for obtaining certification for use with pressure (PED or ASME, depending on the geographical area).
The selection of quality steels with certain characteristics is not only a regulatory obligation, which guarantees safety during transport and storage. Due to the materials contained in these vessels, which are often flammable or difficult to manage, the choice of the right steel also affects the efficiency and duration of the tank over time.