| Abstract: | Highly corrosion resistant special steels for flue gas desulfurisation plants Highly corrosion resistant stainless steel grades have been proved under the severe corrosion conditions existing in flue gas desulfurisation scrubbers (FGD). Besides general corrosion pitting, crevice corrosion and eventually stress corrosion cracking can occur. Thus highly alloyed special steels must be used. Steel grades with a minimum content of 2.75% Mo are essential. At higher chloride levels and decreasing pH-values higher alloyed stainless steels containing up to 6% Mo are necessary. Some of these special steels are described in view to their composition and mechanical properties; their corrosion behavior has been tested under laboratory and field conditions. The use of nitrogen alloyed grades has been shown of remarkable advantage. Nitrogen additions enhance the mechanical properties and structure stability. Furthermore the precipitation of deleterious intermetallic compounds during heat treatment will be delayed by nitrogen additions, thus e.g. multi layer weldings can be carried out with higher security in view to corrosion resistance and mechanical properties. Materials selection for the different scrubber systems will be illustrated by examples. Up to now experiences about stainless steel components in FGD plants are taken into consideration. Welding with distinctly higher alloyed filler metal at the medium-touched side has been well proved in view to adequate corrosion properties. |
