On the Corrosion Behavior of a ferritic 18 Cr-2 Mo-steel

The investigations carried out with 18 Cr-2 Mo steel were aimed at its behavior under pitting corrosion, crevice corrosion and stress corrosion cracking conditions. This was done in autoclave laboratory experiments and under experimental heat exchanger conditions in Rhine river water with a chloride content of max. 400 ppm. The test temperatures were 80, 100 and 130°C. Model heat exchangers were fabricated and operated to investigate the influence of filler materials and weld joints between the ferritic 18 Cr-2 Mo steel and a standard austenitic steel. The possibilities of fabricating tube sheets by applying a weld overlay and using explosive bonding were explored. 18 Cr-2 Mo steel has been shown to be suited for applications in cooling water systems which have a chloride content of 400 ppm. No stress corrosion cracking occurs under such conditions. Tubes with a wall thichness up to 3 mm have sufficient toughness. Tube sheets can be made of boiler plate protected by an explosive cladding or a weld overlay of 18 Cr-2 Mo. A combination of Type 321 or 304 L and 18 Cr-2 Mo is possible. Provided 18 Cr-2 Mo is sufficiently resistant to the product to be cooled, it is an alternative to austenitic CrNi-(Mo) steels (e.g. AISI 304) when stress corrosion cracking is likely to occur.