The unique advantage of stainless steel For a wide variety of applications, stainless steel competes with carbon steels supplied with protective coatings, as well as other metals such as aluminium, brass and bronze. The success of stainless steel is based on the fact that it has one unique advantage. The chromium in the stainless steel has a great affinity for oxygen and will form on the surface of the steel at a molecular level a film of chromium oxide.
Stainless steel can be selected for use compared to other materials for a number of different reasons, not just its resistance to corrosion. These include Its aesthetic qualities: it can be polished to a satin or mirror finish. ƒ “Dry Corrosion” occurs to steel at higher temperatures where it oxidises or scales up. Stainless steel is far more resistant to this than ordinary carbon steel and grades such as 310 (25% chromium 20% nickel) were specifically developed for use at high temperatures. ƒ Non-contamination of the liquids stainless comes into contact with because there is no coating to break down and dissolve. ƒ Weight savings: as thinner sections can be used, more innovative design structures can be used, with cost savings on foundations and platform weights. ƒ Many anti-corrosion coatings are fire hazards or the materials themselves have a low melting point.
Food Production and Storage:
Very large amounts of stainless steel are used in food production and storage. The most commonly used grades are 304 and 316. Typical uses would be dairies, milk storage, ham curing, frozen and salted fish storage. Whereas 304 is used for normal temperatures and acid concentrations, 316 is used for harsher environments. For example, 304 is used in cheese production, but where salted ham is being prepared 316 is used. For low concentrations of phosphoric acid (one of the constituents of cola) 304 is used, but at higher temperatures and concentrations 316 is used. Food slicers are made out of 420 and 440. Very often in food production stainless is used not because the food itself is corrosive but the use of stainless allows for faster and more efficient cleaning. For example, in ice cream production 316 is specified so that strong anti-bacteriological cleaning and rinsing systems can be used. One of the great advantages of stainless steel is that imparts no taste to the food that it comes into contact with. This has created one interesting anomaly. Traditional winemaking uses barrels of oak. The newer wine-producing nations use very large vats and storage containers of stainless steel as this gives them far greater economies of scale. However, in conventional winemaking, the acid of the wine dissolves some of the wood to give an “oak” body taste. Using stainless steel vats oak chips deliberately have to be put into the vats to create the same effect and satisfy traditional wine drinkers.
The pumping and Containment of oils:
The pumping and containment of oils, gases and acids have created a large market for stainless tanks, pipes, pumps and valves. The storage of dilute nitric acid was one of the first major success stories for 18/8 stainless steel as it could be used in thinner sections and was more robust than other materials. Special grades of stainless have been developed to have greater corrosion resistance. These are used in desalination plants, sewage plants, offshore oil rigs, harbour supports and ships propellers.
Architecture is a growing market. Many modern buildings use stainless for cladding. When reinforced concrete first started to be used it was considered that the carbon steel used would not rust as cement, obviously derived from limestone, is alkaline. However, constantly using grit salt on bridges can change the pH to acidic thereby rusting the steel which expands and cracks the concrete. Stainless steel reinforcing bar, although initially expensive, is proving to have very good life cycle costings. The low maintenance cost and anti-vandal characteristics of stainless provides a growing market in public transport, ticket machines and street furniture. :
Nuclear Power Industry:
The nuclear power industry uses large quantities of stainless, often specified with a low cobalt content, for both power generation and radiation containment. Special louvred ventilation shafts are made, which are designed to be used in emergencies Page 6 of 6 to seal off plants for years if necessary. Steam and gas turbines use stainless because of its corrosion resisting and heat resisting qualities.
Especially clean melted stainless is used for medical implants and artificial hips. A great deal of medical equipment – such as orthopaedic beds, cabinets and examination machines – is made as standard from stainless because of its hygienic and easy-clean qualities. Pharmaceutical companies use stainless for pill funnels and hoppers and for piping creams and solutions.
Cars are making increasing use of stainless steel, primarily for exhaust systems (grade 409) and catalytic converters, but also for structural purposes. With greater attention being made to achieving low long-term maintenance costs, less environmental impact and greater concern with life-cycle costs, the market for stainless steel continue to improve.
Source: Word Stainless Association