Stainless Steel Wine Tanks - What You Show Know

Stainless steel is the generic term for grades of steel that contain more than 10% chromium, with or without other alloying elements. Stainless Steel may also have varying additions of Nickel, Molybdenum, Titanium, Niobium and other elements. Stainless steel resists corrosion, maintains its strength at high temperatures, and is easily maintained. The chromium in the steel combines with oxygen in the atmosphere to form a thin, invisible layer of chrome-containing oxide. The most common grades of stainless steel are:

TYPE 304 - The most commonly specified austenitic (chromium-nickel stainless class) stainless steel. This grade withstands ordinary corrosion such as mild acids and sulfite found in wine, beer and olive oil, and is durable in typical food processing environments, and resists most chemicals. Type 304 is available in virtually all product forms and finishes.

TYPE 316 - Austenitic (chromium-nickel stainless class) stainless steel containing 2%-3% molybdenum (whereas 304 has none). The inclusion of molybdenum gives 316 greater resistances to various forms of deterioration.
Type 316 is recommended for the roofs of closed top tanks due to potential of high concentrations of corrosive gasses and liquids produced by the sulfites in wine.

Stainless steel can be welded by three methods; ARC, Metal Inert Gas (MIG) or Tungsten Inert Gas (TIG).

ARC welding employs a stainless steel rod coated with a formulation of chemicals to provide a flux to bond the metal, sustain an arc and to provide a barrier to reactive gases such as oxygen.
MIG welding works by continuously feeding a wire to the metal being welded surrounded by an envelope of non-reactive gas such as Argon, Carbon Dioxide, and or Helium. For stainless steel a mixture of the above three gasses are employed. MIG welding is a quick method of welding allowing a continuous weld. This welding is employed in the manufacture of tanks but leaves a raised bead both inside and outside the tank. Having a bead on the outside is cosmetic but having a bead on the inside of the tank makes it hard to clean and keep sanitary.

TIG welding employs the use of a tungsten rod surrounded by an inert gas such as Argon to provide arc stability and a non-reactive atmosphere at the weld. The rod and the gas provide the heat to melt the metal of the joint being welded and the stainless steel filler rod. This is similar to gas welding or brazing. This method of welding takes great skill to perform but leaves a smooth flawless seam on both sides of the weld. Very little grinding is necessary.

Before signing a contract to purchase a tank, ask the vendor or manufacture where they source their material. Ask for a copy of the material manufactures datasheet to insure it is certified by a testing agency to be the material it is propertied to be. Look at the welds both on the inside and outside of the tank. Look at how the ports and man-ways are attached to the tank. Do they have smooth radius transitions or are they protruding on the inside making cleaning and sanitizing difficult.

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