Caustic soda and chlorine are co-produced by the electrolysis of a sodium chloride solution. Both chemicals find worldwide application in the chemical and related process industries. Caustic soda ranks third in tonnage production among the inorganic chemicals; worldwide annual consumption is around 65 million tonnes. In general, factors to be considered in materials selection include practicality, safety and health aspects, availability, mechanical properties, corrosion resistance, risk/benefit considerations and economics.