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Grades 1.4301, (304), 1.4401, (316) and 430, (1.4016), are compared for food contact applications. A list of typical applications for martensitic 1.4028, (420), and 1.4116, ferritic, 1.4016, (430), austenitic, 1.4301, (304), 1.4401, (316) and 1.4539, (904L), austenitic 1.4362 and 1.4462, (2205), duplex and 1.4547, (254SMO), superaustenitic types is presented. Corrosion hazards in food applications, i.e. pitting crevice and stress corrosion cracking are discussed. Suitable cleaning and disinfection systems should avoid the use of hypochlorite or chloride solutions.
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Localised corrosion mechanisms pitting, crevice and stress corrosion cracking are mentioned, but normally stainless steels are considered “inert” in supply, (or town’s), waters. The affect of chloride levels, temperature, oxygen levels, flow rates and bacterial oxidants, i.e. chlorine on the resistance of stainless steels in waters is discussed. Crevice corrosion should be rare at chloride levels below 200 and 1000 ppm, (mg/lt), respectively, for 304, (1.4301 / 1.4307), and 316, (1.4401 / 1.4404), types. Water chloride ranges for duplex 1.4462, (2205), super austenitic, 254SMO, (1.4547), and super duplex types SAF2507, (1.4410), and Zeron 100, (1.4501), are also shown.
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This Health and Safety Executive Sector Information Minute SIM 5/2002/18 outlines the background to stress corrosion cracking failure hazards to stainless steel items used in indoor swimming pool buildings. This follows on from roof failures in Switzerland in 1985 and more recently in the Netherlands and notes that the atmospheres of indoor swimming pool buildings are amongst the most aggressive ones found in building interiors, where stainless steels are used. The minute discusses the background, noting the effects of chlorine based water disinfection systems and the chloramines generated by body fluid excretions on stainless steel components under applied or residual tensile stress. The stress corrosion process is outlined and the susceptibility of grades 1.4301, (304) and 1.4401, (316), to SCC in swimming pool environments noted. Preventative measures, inspection procedures and recommended actions for HSE inspectors are also covered.
