GREY CAST IRON PIPES
The manufacture of cast iron pipes began as an offshoot of cannon founding in western Europe. Early iron pipes were cast horizontally, and pipes conveying water in Palace of Versailles survived for more than 400 years. Metallurgically, the pipes consist of carbide, phosphides and carbon, offering very good corrosion resistance – hence the reason for their longevity.
A significant technological development occurred in late 1800’s when vertical casting replaced horizontal casting. These pipes also contained large amounts of phosphorus to enable fluidity in casting, and also exhibit good corrosion resistance. A socket, or bell, was formed during the casting, enabling the spigot-socket jointing method. Other features of this pipe are eccentric and relatively thick pipe walls, and typically, lead jointed.
Further development occurred in the early 20th Century, whereby iron was cast into spun water-cooled steel moulds, which produced thinner walled “whited” cast iron, which subsequently required heat treatment to form grey cast iron. The socket was formed using a disposable sand core. Annealing produced a predominantly ferritic matrix with flake graphite of varying morphologies. Corrosion resistance of these pipes appears to be less than the older statically cast pipes.
Spun grey cast iron pipes are usually cement lined. Jointing can vary from lead to rubber ring, depending upon age. Coatings can also vary, from essentially thin tar or bitumen, to coal tar epoxy, and loose polyethylene sleeving.
Grey cast iron pipes exhibit little or no ductility, and can undergo “catastrophic” failures, with little or no corrosion. They undergo a phenomenon referred to as “graphitisation”, whereby the ferritic matrix “dissolves” and leaves a graphite-cementite remnant, which retains the exact shape and size of the parent metal, and although structurally weaker than uncorroded iron, can withstand modest levels of hydrostatic loading.
Ultimately this material was replaced by spheroidal graphite cast iron, commonly referred to as Ductile Iron.
Spun Grey Cast Iron Tubemakers Yennora.
Installation in Versailles, France
Delavaud centrifugal casting
Cast Iron pipes used in Sydney to supply water from local swamps
Factory cement lining.
Spun Cast Iron AIS Port Kembla.
Cast Iron Microstructure