Manual of CPHEEO ( Water Supply)

TRANSMISSION OF WATER

6.4 CAST IRON PIPES

6.4.1 General

Most of the old Cast Iron pipes are cast vertically but this type has been largely superceded by spun iron type manufactured upto a diameter of 900 mm. Though the cast iron pipe has the disadvatages of heavy weight, and consequent high transport costs, short length, leading to higher laying and jointing cost, low tensile strength, liability to defect of inner surface, it is widely used because of its good lasting qualities. There are many examples of cast iron mains in this country which continue to give satisfactory services even after a century of use.

Cast of Iron pipes and fittings are being made in this country for more than a century. The production capacity exceeds more than 3,00,000 tons per annum. Due to its strength and corrosion resistance , C.I pipes can be used in soils and for water of slightly aggressive character. They are well suited for pressure mains and laterals where tapping are made for house connections. It is preferable to have coating inside and outside of the pipe.

Vertically cast iron pipes shall conform to IS 1537 -1976. The pipes are manufactured by vertical casting in sand moulds. The metal used for the manufacture of this pipe is not less than grade 15. The pipes shall be stripped with all precautions necessary to aviod wrapping or shrinking defects. The pipes shall be such that they could be cut, drilled or machined.
Cat Iron flanged pipe and fittings are usually cast in the larger diameters. Smaller sizes have loose flanges screwed on the ends of double spigot spun pipe.

The method of Cast Iron pipe production used vniversally today is to form pipes by spinning or centrifugal action. Compared with vertical casting in sand muulds, the spun process results in faster production, longer pipes with vastly improved metal qualities, a smoother inner surface and reduced thickness and consequent light weight.

Centrifugally cast iron pipes are available in diameters from 800mm to 900 mm inclusive and are covered with protective coatings. Pipes are supplied in 3.7 m to 5.5 meters lengths and a variety of joints are avialable including socket and spigot and flanged joints.

The pipes have been classified as LA,A and B according to their thicknesses. Class LA pipes have been taken as the basis for evolving the series of pipes.

Class A allows a 10% increase in thickness over Class LA.

Class B allows a 20% increase in thickness over Class LA.

The pipes are either spigot and socket type and available with a nominal diameters ranging from 80mm to 900mm. When the pipes are to be used for conveying potable water the inside coating shall not contain any constituent soluble in water or any ingradient which could impart any taste or odour whatsoever to the potable water after sterilisation and suitable washing of the main.

Experinments in centrifugal casting of iron pipes were started in 1914 by a French Engineer which ultimately resulted in commerical production of spun pipes. Spun pipes are about 3/4 of the weight of vertically cast pipes of the same class. The greater tensile strength of the spun iron is due to close grain allowing use of thinner wall than for that of a Cast Iron pipe of equal length. It is possible by this porcess to increase the length of the pipe whilst a further advantage lies in the smoothness of the inner surface.