Corrosion studies of austenitic and duplex stainless steels in the environment of ferment of biogas plants

In the present paper, the study of pitting and general corrosion of stainless steels used in agriculture, specifically for the agricultural biogas plant constructions, is presented. The austenitic stainless steels AISI 304L, AISI 316Ti, and duplex steel 2205, were investigated. For the evaluation of corrosion resistance, the potentiodynamic studies were performed. General corrosion was determined in the Tafel region of potentiodynamic curve, while pitting corrosion was examined on the basis of the pitting corrosion initiation potential. Based on the studies carried out, it can be stated that the alloyed cold-rolled austenitic stainless steel AISI 304L placed in the environment of the biogas plant ferment has the lowest resistance to pitting and general corrosion of all studied steels. The cold-rolled duplex stainless steel 2205 placed in the same corrosive environment revealed the highest resistance to these types of corrosion. It should be also noted that the pitting and general corrosion resistances of tested alloy austenitic stainless steel AISI 316Ti are higher than those ones of AISI 304L, and less than those ones of duplex steel 2205. In conclusion, as could be expected, the best material for the biogas plant construction is duplex stainless 2205 because it shows the highest resistance to both types of corrosion studied. This steel can be advised as a material for construction of fermentation tanks and heating installations for mixture ferment.