Q. What is Carbon steel?

Carbon steel has long been used for handling concentrated sulphuric acid under ambient temperature and low velocity conditions. In service, a soft sulphate protective film is formed on the carbon steel surface, but if disturbed, accelerated corrosion rates will occur. The general corrosion mechanism is such that iron plus sulphuric acid reacts to produce iron sulphate and hydrogen. At high concentrations the iron sulphate corrosion product will form a soft tentatively stable protective film, thus achieving relatively low corrosion rates at generally acceptable levels of less than 5 mpy (.125 mmpy).

Typically, carbon steel is used for handling concentrations of 93% to 98% H2SO4 at temperatures below 100°F (38°C) and under static or low flow conditions. At lower concentrations of less than 70% concentration the iron sulphate corrosion product readily dissolves and corrosion rates increase to less than acceptable rates.