3.2.1.2 Carbon steel

Carbon steel is used in vacuum technology, as long as pressures of less than about 1 · 10^-5 hPa do not need to be created and maintained and corrosion protection is not required. Compared to stainless steel it is a relatively low-priced building and construction material, which has good weldability and is easy to process. However the continuous outgassing of CO and the tendency to corrode from air must be taken into account when this type of steel is used. On the atmosphere side corrosion protection can be provided by painting, while on the vacuum side this can be provided by nickel plating. For tank construction, the steel grades used must be chosen carefully, especially where weldability and tightness are concerned. Boiler construction methods are only transfer- able to a limited extent to vacuum vessel construction. When dimensioning, the stress caused by the external atmospheric pressure must be considered and welding must ensure a vacuum-tight seal. In addition, the tools used must be strictly separated from those that are used for processing stainless steel, to avoid contaminating the stainless steel. The same applies for storing and transporting mild steel and stainless steel. Mild steel is often used for fasteners for flange connections, where the surfaces are zinc, nickel or chrome plated to protect them from corrosion.