The food industry uses various corrosion resistant alloys (CRA's) in the form of vessels, piping, mixers, etc. to process different types of foods. The physicochemical characteristics of processed foods permit various CRA grades depending on the type of food contents and its corrosivity (non-corrosive, mild, medium, and high corrosivity). Due to ease of availability and low cost 304 stainless steel (UNS S30400) is the most commonly used CRA in the food industry. If proper heat treatment is not performed on the 304 stainless steel food processing components, when subjected to low pH corrosive environments, the welds and heat affected zone (HAZ) show poor corrosion resistance.
In this study, the corrosion resistance of 304 stainless steel weld metal in low pH environments, involving a high viscosity, low pH (3.6) "food product" and lime juice was investigated via electrochemical corrosion tests. A series of electrochemical linear polarization resistance (LPR) corrosion rate measurements of sensitized 304 weld and non-sensitized 304 and 316 stainless steel welds in the above-mentioned environments are performed at room temperature and 40°C to determine the general corrosion behavior and pitting corrosion resistance. Metallographic examination and scanning electron microscopy (SEM) examination of the tested welds were performed. Sensitized areas of 304 stainless steel showed higher corrosion rates and poor pitting resistance. The study demonstrated that a non-sensitized weld of food processing equipment is very important to prevent corrosion in low pH foods.
Food consists mainly of proteins, carbohydrates, and fats. Processed foods contain diverse aqueous solutions, syrups, and additives, used to improve food appearance, taste, quality and preservation. They have a wide pH range, components such as, salt, water, and vinegar impact food corrosivity.1
Modern science and technology have enabled the development of an extended range of materials with increased corrosion resistance, improved mechanical strength, easier forming and fabrication, weldability, and health friendly features. The workhorses of food processing industry are stainless steels 304 (UNS S30400) and 316 (UNS S31600), but other austenitic and duplex SS are in useful service in food plants.2