Materials of Construction - Grey Cast Iron
October 25, 2003

Introduction

Grey cast iron is essentially an alloy of primarily iron, carbon and silicon with manganese, sulphur and phosphorus in minor amounts.  The carbon is present as free carbon or graphite interspersed throughout the mass of metal.  In grey cast iron, the graphite is in the form of flakes while in ductile cast iron, the graphite is in the form of nodules.  Cast iron is easily machined because the graphite in the iron acts as a lubricant during machining.

Grey cast iron is no longer recommended for use in sulphuric acid plants.  in the past, there have been instances where acid lines have been accidentally struck and have failed catastrophically.   Ductile iron should only be used in sulphuric acid service.