Fittings made of acid-resistant and stainless steel are widely used in industry. They come in both weld-on and threaded forms, and are made into pipe clamps, flanges, caps, and industrial and food-grade valves. In the processing sector in particular, acid-resistant fittings play an invaluable role. What are the most important properties of acid-resistant steel – and is it in any way harmful to consumers?
What is acid-resistant steel?
Acid-resistant steel is steel that withstands acids weaker than sulphuric acid. As with austenitic stainless steel, it is produced by alloying iron with chromium and nickel, although the content of those elements is usually higher than in ordinary stainless steel. Other alloying additions – titanium, copper or manganese – go into acid-resistant steel as well. It is normally used after polishing.
Properties of acid-resistant steel
Acid-resistant steels, like stainless ones, are classified according to specialist standards. Poland follows the European standards, under which acid-resistant steels count as stainless steels. The most popular stainless material is the grade covered by AISI 304. It welds well and is widely used in the food and chemical industries. AISI 304 resists corrosion and also stands up to certain organic and inorganic acids.
AISI 321 contains an addition of titanium, which gives it considerable resistance to intergranular corrosion. It can be used at temperatures up to 800 degrees Celsius. The most popular acid-resistant steels, however, are AISI 316, 316L and 316Ti. Materials to these standards perform excellently in aggressive environments and are used in the chemical, dyeing, pharmaceutical and food industries.
Acid-resistant fittings in the food industry
As with stainless steel, acid-resistant steel is widely used in the food industry – above all for installations carrying brines. It is also often used in processes connected with the production of alcohol. Because acid-resistant steel belongs to the stainless family, it does not react chemically with food. More than that: HACCP standards positively require stainless steel wherever there is contact with foodstuffs. The passive chromium oxide film responsible for the steel’s anti-corrosion properties repairs itself, so the material keeps working even after being machined. It also needs no regular, costly maintenance, and it is ideal for carrying food intermediates such as marinades and brines.
Acid-resistant fittings are particularly well suited to the processing industry. Their hygiene, longevity and strength make them ideal as installation components in machinery. Food-grade valves and flanges of every kind cope well even in difficult, acidic environments and keep working for a long time. Using stainless steel in the food industry therefore pays off for the producer and the end consumer alike.
