Info

W 3.0-4.5, V 0.35

Note: Unless indicated otherwise, all values are maxima.

Note: Unless indicated otherwise, all values are maxima.

riety of materials of construction. Because of the position in the electrochemical series (to be discussed later), aluminum and its alloys are susceptible to galvanic corrosion when coupled with other metals.

2. The commercial availability of stainless steels and their ease of fabrication, strength, ease of maintenance, appearance, and proven track record of reliability.

3. The fact that since modern plants operate on a semi-continuous basis with much higher levels of fouling, cleaning regimes require strongly alkaline detergents to which aluminum has virtually zero corrosion resistance.

Copper and Tinned Copper

Copper and tinned copper were used extensively in former times because of their excellent thermal conductivity (8 times that of stainless steel), ductility, ease of fabrication, and reasonable level of corrosion resistance. However, the demise of copper as a material of construction is largely attributable to the toxic nature of the metal and its catalytic activity in the development of oxidative rancidity in fats and oils. Even at the sub-part-per-million level, copper in vegetable oils and animal fats rapidly causes the development of off-flavors. In equipment where high levels of liquid turbulence are encountered (eg, plate heat exchanger or high-velocity pipe lines) copper is subject to erosion. Nevertheless, there is an area of the beverage industry where copper is still the only acceptable material of construction, ie, pot stills for Scotch and Irish whiskey production. It is also used in the distillation of the spirits such as rum and brandy. Much old copper brewing equipment such as fermenting vessels and wort boilers is still in use throughout the world, and an interesting observation is that even though the wort boilers in modern breweries are fabricated from stainless steel, they are still known as "coppers" and UK craftsmen fabricating stainless steel are still known as coppersmiths.

Titanium

There are certain areas of the food industry, especially in equipment involving heat transfer, where stainless steels are just not capable of withstanding the corrosive effects of salty, low-pH environments. Food processors are increasingly accepting the use of titanium as an alternative, in the full knowledge that it offers corrosion immunity to the more aggressive foodstuffs and provides a long-term solution to what was an on-going problem with stainless steels. Titanium is a light metal, the density of which is almost half that of stainless steels. Although relatively expensive (6-7 times the cost of stainless steel), being a low-density material offsets this price differential for the raw material by almost half. It is ductile and fabricable using normal techniques, although welding it does require a high degree of expertise.

Other Metals

Tin, in the form of tin plate, is used extensively in the canning industry, where its long-term corrosion resistance to a wide range of food acids makes it a material par excellence for this purpose.

Cadmium, used as a protective coating for carbon steel nuts and bolts, was favored at one time. However, the high toxicity of the cadmium compounds has come under increasing scrutiny from many health regulatory bodies and now cadmium-plated bolting is not permitted in food factories. Indeed, Denmark and Sweden have totally banned the import of cadmium-plated components into their countries, and many other countries are likely to follow suit.

Lead and lead-containing products are generally not acceptable for food contact surfaces, although some codes of practice permit the use of lead-containing solder for capillary pipeline joints on water supplies and service lines.

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