To reduce the air pollution caused by fossil energy boilers, flue gas desulfurization units are more and more used in North America, European countries and Asian. The most common technology consists of scrubbing the polluted gas with a slurry of lime or limestone in water. In certain zones of scrubber (absorber) where the reaction between polluted gas and the solution is not complete, acidic condensation can occur and, combined with high temperatures, chlorides and/or fluorides, lead to very aggressive conditions. Generally, metallic materials present the best solution in terms of reliability ad cost. Since the corrosion
resistance of standard stainless steels, such as 316L, is very limited in such environments, highly alloyed stainless steels or nickel based alloys are generally used for the most corrosive conditions. Building scrubber units require welded materials. Welded joints are made-up of different zones : thermal cycles induce structural modifications, filler materials induce chemical composition variations, and weld beads induce geometric variations. Welds are very often the weak point for the corrosion resistance. To increase the corrosion resistance of the welds, new stainless steel materials with improved weldability have been developed proposing higher corrosion resistance properties (> 6 MO grades, NO8926 or S32050) or high corrosion resistance and high mechanical properties (duplex S3 1803/S32205 and superduplex
S3255O/S32520). More recently, a high nitrogen overalloyed austenitic grade (S31266) providing very high corrosion resistance and high mechanical properties has been developed. This new grade with high nitrogen content (0.45% by weight) exhibits exceptional corrosion resistance properties in both unwelded and welded conditions. Nickel based alloys have been also investigated both in solid and clad
materials. The aim of this paper is to evaluate and compare the behaviour of these materials in simulated FGD environments, particularly in welded conditions. Several tests representative of industrial conditions have been selected. Test conditions simulating the very corrosive environments of gas cleaning systems : low pH, high temperature and high chloride levels have been investigated. The critical conditions have been determined for each material in unwelded and welded conditions. The results are discussed in terms of technical efficiency and potential applications.
