ABOUT GLASS

Glass lined equipment is used in a wide range of chemical processes that involve harsh chemicals, including the production of pharmaceuticals, chemicals, petrochemicals, agricultural and… industries. One of the reasons for the attraction is that glass is resistant to attack from most chemicals and to mixtures of corrosive materials. In addition, it has a smooth, anti-stick surface, is easy to clean, and does not transfer impurities to the process materials.

The metals that compete with glass for corrosion resistance are tantalum, titanium and zirconium, all of which are several times more expensive than glass lined equipment. Glass lined can be used with most acid or alkaline media, since glass withstands attack from most substances in both oxidizing and reducing environments. The exceptions include fluorides at any temperature or concentration; hot, concentrated phosphoric acid; and highly alkaline chemicals at high temperatures.

Glass lined vessels typically consist of a carbon-steel body with a bonded inner lining of specially formulated glass. The glass is composed of several oxides and silicates. It is blended and heated to the melting point, emptied through a chute, quickly cooled and solidified into particles called frit. The first coat of glass applied to the steel is the ground coat; it has limited corrosion resistance and is used solely to develop a chemical bond with the base metal. After the ground coat is cooled, the chemically resistant glass is applied. This procedure is repeated until a desired glass thickness is achieved, which is usually 40-90 mils.

Equipment that is often supplied with a glass lining includes reactors, storage tanks, bolted tanks, columns, pipes and fittings and valves. The internal components of the vessels, such as agitators, baffles and dip pipes, are also supplied with glass coatings. In general, glass-lined vessels are designed to operate at temperatures up to 500 °F (220°C) and pressures of 130-150 psig (9.14–10.55 kg/cm2), although they can be built to withstand much higher pressures.

The leading cause of problems in the operation of glass-lined equipment is mechanical damage resulting from impact, and the second is thermal shock, caused by heating or cooling a vessel too quickly. These and other problems can be avoided or minimized by proper operation of the equipment and by educating personnel in the procedures for working with glass-lined equipment. 
 

For more information about corrosion characteristics and thermal shock of glass lined equipment study Shimi Azar Jaam technical catalogue.