The difference is in the micro-structure of the iron. Cast iron pipe for water transmission has been around since the 17th century. Cast iron pipe has great strength but lacks malleability so it is subject to mechanical damage in transit and handling which can be in the form of visually imperceptible hairline cracks. The development of ductile iron technology in 1948 led to a revolution in the iron pipe and fitting industry. Ductile iron is produced using more refined raw material. To the molten iron batch is added a highly controlled amount of magnesium alloy. This produces a drastic change in the microstructure causing the graphite to form spheroids rather than flakes, and a finer grain iron, giving the iron the ductility – making it much stronger, tougher, and resistant to mechanical damage in the form of cracks and outright shattering.