Ductile Iron Spun Pipes (disp) and Cast Iron Spun Pipes (cisp)

General

Ductile iron spun pipes (DISP) and cast iron spun pipes (CISP) both find usages in water supply, sanitation and housing. Cast iron spun pipes have traditionally been the major mode of potable water supply. Other materials have not been able to meet the requirements of this particular sector in a satisfactory way. Steel pipes offer greater strength, but are more susceptible to corrosion, in addition to being costlier.

Grey cast iron contains graphite in the form of flakes, resulting in discontinuities in the matrix. Moreover, the pointed ends of the flakes act as regions of stress concentration, making the material brittle and weak. To overcome this limitation, ductile cast iron has been developed.

Ductile cast iron or spheroidal graphite (S.G.) cast iron is produced by the addition of magnesium or cerium to molten iron, which results in the spheroidization of graphite. This results in the removal of discontinuities and improvement in machinability and abrasion resistance. Ductile iron spun pipes offer mechanical properties similar to that of steel pipes, in addition to good corrosion and wear resistance and the processing and economic advantage of cast iron spun pipes.

In view of the anticipated spurt in demand for DI/CI spun pipes, M/s KIOCL envisages installing a DI spun pipe plant. Thus, it was thought prudent to examine the market scenario of DI spun pipes, as deliberated in the following paragraphs.

A comparison of mechanical properties of CISP, DISP, and steel pipes is illustrated in fig-1.

Fig-1

Advantages of D.I. spun pipes:

The advantages of using ductile iron pipes are as follows:

 Better physical and mechanical properties compared to other pipe materials:

* High tensile and beam strength

* Withstands severe crushing load

* Extremely high impact resistance

 More water carrying capacity, as internal diameter is greater than nominal diameter. The wall thickness of ductile iron pipes can be upto 33% less than that of cast iron pipes and as such it is lighter per unit length.

 Highly corrosion resistant due to smooth inside cement mortar lining

 The ISO, BS, DIN and IS specifications are identical

 Offers high working pressure and safety against water hammer. Ductile iron pipes can withstand about double the hydraulic pressure than cast iron pipes of the same thickness.

 Speedy Laying / Installation procedure.

 Ease in handling - Lightweight and superior mechanical property makes DI pipe easier to handle. Greater torque can be applied while tightening the connections and drilling and tapping do not require any special technique.

 Welding is possible.

Ductile iron pipes possess all the advantages of cast iron pipes and they surpass the limitations of cast iron pipes because of their greater strength, elongation, impact resistance etc. As such, these pipes find application in areas like water supply, sewerage, tubewell casings etc. They have replaced grey cast iron pipes in the field of water supply in developed countries. They have also replaced steel pipes in certain applications due to economic considerations.

The major consumers of DI/CI pipes in India

The major consumer of DI/CI pipes are:

1) Public health engineering departments of various states & statutory bodies including MES, Railways etc.

2) Statutory bodies in charge of urban development including JNNURM (Jawaharlal Nehru National Urban Renewal Mission), Mega City Projects, Bharat Nirman Project, BSUP (Basic Service for Urban Poor) etc.

3) Water supply systems of different industrial projects.

4) Water treatment plants for public and industrial use.

5) Industrial effluent and sewage treatment plants.

6) Housing projects.

7) Irrigation schemes.

8) Sewerage and drainage schemes.

Demand drivers for iron spun pipes

In India water supply is mainly met through monsoons. As a result the focus has been more towards surface water resources. Schemes of holding water in reservoirs for meeting domestic, agricultural and industrial water demand have increased. This has translated into a huge demand for reliable and durable pipes.

Water supply projects in the county are partly funded by the Central Government through various water supply schemes viz. Jawaharlal Nehru National Urban Renewal Mission (JNNURM), Urban Infrastructure Development Scheme for Small and Medium Towns (UIDSSMT), Basic Services for Urban Poor (BSUP), Accelerated Rural Water Supply Programme (ARWSP), Mega Cities Project, Bharat Nirman Project etc. while the rest of the funds are raised by the respective state governments. In addition, the number of water supply & sanitation projects funded by World Bank and other foreign agencies are also increasing in the county. Further, it is expected that the flow of private funds in water supply would increase.

Although, other pipes viz. Asbestos cement pressure pipes, PVC pipes, Pre-stressed cement pipes, Hume steel pipes, Galvanized steel pipes, RCC pipes etc. are used in water supply and sanitation sector, barring the steel pipes which find application in rising mains and special terrain and field conditions, all other types of pipes are used only when the DI/ CI spun pipes are not available or on account of cost considerations. The spun pipes are preferred due to their ability to sustain high pressures, long life span and also because of the fact that whenever corrosion occurs, the corrosion products are strongly adherent to the parent metal and form a protective barrier which checks further corrosion and inhibits further attack. By virtue of good lasting qualities and satisfactory service, the spun pipes had been in the use for water supply and sanitation schemes for more than a century.

The total consumption of water in India is expected to rise by 20-40 per cent over the next