Pipes for Conveyance of Water | Water Conveyance | Water Engineering

Following types of pipes are commonly used for conveyance of water: 1. Cast-Iron Pipes 2. Wrought Iron Pipes 3. Steel Pipes 4. Concrete Pipes 5. Cement-Lined Cast-Iron Pipe 6. Asbestos Cement Pipe 7. Copper and Lead Pipes 8. Wooden Pipes 9. Plastic Pipes 10. Vitrified Clay Pipes.

Type # 1. Cast-Iron Pipes:

Cast-iron pipes are mostly used in water supply schemes. These are highly resistant to corrosion; therefore have long life-about 100 years. Cast-iron pipes are manufactured from best grey pig iron by two methods. First method is ordinary sand moulding in which pipes are moulded in horizontal position. Horizontal casted pipes are also called Mcwane Pipes.

Sometimes in sand moulding pipes are moulded in vertical position, which are called Pit Cast Pipes. In the sand moulding, after casting, the pipe is cleaned, and dipped in a pot of coal tar and oil, after heating to about 300°F.

This coal tar coating is done to protect it against corrosion. Centrifugal casting is the second method, which is sometimes called as Delov and process. In this method, the molten metal is poured in water cooled cylindrical metal mould, which is rotated at high speed. Due to centrifugal force a homogeneous pipe is cast. The pipe is taken out from the mould and sent to another process for annealing. Then it is tested under hydrostatic pressure and coated with coal tar as in the case of sand moulding.

Practically, it has been noted that horizontal cast pipes are 100% strong in tension and 50% stronger in rupture than vertically cast iron pipes.

Cast-iron pipes are manufactured in lengths of 2.50 m to 5.50 m. The fittings of these pipes are also manufactured in sand moulds having core boxes. These fittings are also weighed, coated with tarcoal and finally tested. Cast-iron pipes are joined together by means of Bell and Spigot, threaded or flanged joints.

These pipes have the advantages of easy jointing withstanding high internal pressure, long life and less corrosion. But these are very heavy and difficult to transport, because due to brittleness they break or crack easily. Therefore, these are most suitable as distribution pipes.

Centrifugally cast-iron pipes are generally available in India in three categories.

I.S. 1536-1967 designates their categories as under:

Table 7.2 gives the test pressure for vertically C.I. pipes as for I.S.:1537

Type # 2. Wrought Iron Pipes:

Wrought iron pipes are manufactured by rolling the flat plates of the metal to the proper diameter and welding the edges. If compared with cast iron, these are more lighter, can be easily cut, threaded and worked; give neat appearance if used in the interior work.

But it is more costly and less durable than cast iron pipes. These pipes should be used only inside the buildings, where they can be protected from corrosion. Wrought iron pipes are joined together by couplings or screwed and socketed joints. To increase the life of these pipes sometimes these are galvanized with zinc.

Type # 3. Steel Pipes:

The construction of these pipes is similar to wrought iron pipes, it is occasionally used for main lines and at such places where pressures are high and pipe diameter is more. Steel pipes are more strong have very light weight and can withstand high pressure than cast iron pipes. They are also cheap, easy to construct and can be easily transported than cast iron pipes.

The disadvantage of these pipes is that they cannot withstand external loads, if partial vacuum is created by emptying a pipe rapidly, the pipe may be collapsed or distorted. These pipes are much affected by corrosion and are costly to maintain. The life of these pipes is 25 to 50 years which is much short as compared with cast iron pipes. Steel pipes are not used in distribution system, owing to the difficulty in making connections.

The joints in steel pipes may be made by welding or riveting. Longitudinal lap joints are made in riveted-steel pipes up to 120 cm diameter. In case thickness of steels plate exceeds 15.87 mm, but joints are provided. If the diameter of the pipe is very large, two longitudinal seams may be provided. When the pipe has to be more stiffer it can take more earth load without collapsing. Welded steel pipes can be used for large diameters upto 2.43 m or even more.

Type # 4. Concrete Pipes:

These pipes may be precast or cast-in-site. Plain concrete pipe may be used at such places where water does not flow under pressure. These pipes are jointed with Bell and Spigot joints. Plain concrete pipes are used up to 60 cm diameter only, above it these are reinforced.

R.C.C. pipes are manufactured by the following methods:

(i) Pipes having steel bar and mesh reinforcement, and by pouring concrete by usual methods, tamping and curing.

(ii) Pipes having fabricated reinforcement and cast by centrifugal methods and curing in tanks.

Precast pipes are manufactured in factories and then transported to the site. The reinforcement of R.C.C. pipe consists of a welded steel cylinder with high tension wire wound over it. The concrete is placed around the reinforcement by centrifugal process.

Sometimes mesh reinforcement is provided, but pipes with cylinder pipe reinforcement are more water tight and strong. Normally 1:2:2 concrete mix is used in the manufacture of concrete pipes. Larger diameter pipes are jointed together by means of collar joint with a rubber gasket or fibre filled lead gasket placed between the two ends of the pipes.

In difficult areas pipes can be constructed at the site by using local materials. These are not corroded by the water, therefore, have long life, above 75 years. The surface of these pipes is not affected with the time; therefore, the carrying capacity does not reduce. The maintenance cost is low. But they are very heavy and difficult to handle and transport. They cannot withstand high pressure and are difficult to repair.

Normally R.C.C. pipes are made from 1:2:2 cement: sand and aggregate. The maximum size of the aggregates is kept as 7 mm. For carrying tension they are provided with circumferential reinforcement. 0.25% longitudinal reinforcement is provided in the pipes. Thickness of the pipes varies from 25 mm to 65 mm for pipe diameters varying from 10 cm to 120 cm.

Now a days prestressed concrete pipes are also available in the market, but these are not common. Various available standard sizes of the concrete pipes are: 80, 150, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100 and 1200 mm. These diameters are internal diameters of the pipes.

Table 7.4 gives specifications of ordinary R.C.C. pipes as per I.S.: 458-1971:

Type # 5. Cement-Lined Cast-Iron Pipe:

When the water contains corrosive elements, the cast-iron pipes are lined with cement to protect them against corrosion. Lining of 1:2 cement mortar is applied centrifugally inside the pipe. The thickness of lining varies from 3 mm to 6 mm.

After lining, it is properly cured. Cement lined pipes have very small coefficient of friction than unlined cast iron pipes. Cement lining is not injured by cutting or drilling the pipe. Sometime after long use cast iron and steel pipes of large diameter are given cement lining by means of centrifugal machine. Table 7.5 gives the specifications of steel cylinder R.C.C. pipes as per I.S. 1916-1963.

Advantages of R.C.C. Pipes:

(i) Their life is more-about 75 years.

(ii) They can be easily constructed in the factories or at site.

(iii) They have least coefficient of thermal expansion than other types of pipes. Hence they do not require expansion joint.

(iv) Due to their heavy weight, when laid under water, they are not affected by the force of buoyancy, even when they are empty.

(v) Under normal traffic loads, when laid below roads, they do not collapse or fail.

(vi) They are not affected by atmospheric actions or by ordinary soil under normal conditions.

Disadvantages of R.C.C. Pipes:

(i) They are affected by acids, alkalies and salty waters.

(ii) Their repairs are very difficult.

(iii) Due to their heavy weight, their transportation and laying cost is more.

(iv) It is difficult to make connections in them,

(v) Porosity may cause them to leak.

Type # 6. Asbestos Cement Pipe:

These are manufactured from a mixture of cement and asbestos fibre. The mixture of cement and asbestos is first placed over a rotating steel mandrel in uniform thickness and then is pressed by means of steel pressure rolls. The steel rolls compact the mixture into a dense and homogeneous mass.

These pipes are manufactured from 5 cm to 130 m in diameter and in five different grades to withstand internal pressure from 3.5 kg/cm². These pipes are not affected by salts, acids and other corrosive materials and remain smooth.

Asbestos cement pipes are very light, therefore, can be easily handled and transported. They can be easily cut, fitted, drilled, trapped and jointed. These pipes are very smooth (Hazen Williams co-efficient being 140) and are not affected by corrosive materials, therefore have good carrying capacity. But these are costly and break or crack during transport because they are very brittle. These pipes are suitable for small size distribution pipes.

A.C. pressure pipes are becoming more and more popular. These pipes are classified according to the best pressure as given in Table 7.6.

The nominal diameter of these pipes are 50,80,100,125,200,250,300,450,600,900 and 1000 mm. The nominal effective length (length between extremities for pipes with plain ends and effective length for pipes with socket) is not less than (a) 3 m for pipes of nominal diameter 100 m or less, and (b) 4 m for pipes of nominal diameter greater than 100 mm.

The maximum working pressure should not exceed half the test pressures given in Table 7.6. The variation of the internal dia. shall not be more than 10% of the nominal internal diameter.

Type # 7. Copper and Lead Pipes:

Copper pipes are not liable to corrosion, even if water contains some traces of acids. These pipes can be easily bent and also do not sag if used for hot water supply. These pipes are only used in making gouseneck in the house connections and carrying hot water inside the buildings.

Lead pipes are not used in India, because they cause lead poisoning. But they can be given bends easily and also can withstand high pressure. These pipes are mostly used in sanitary fittings. In water-supply these are used in chlorination and alum dosing. These pipes cannot be used for hot water supply, because they sag under such circumstances.

Type # 8. Wooden Pipes:

Wood is being used since long for the construction of pipes. Modern wood pipes are manufactured from staves and are of two types. First type is machine banded pipe which is manufactured in small lengths at the factory. Second type is continuous pipe which is assembled on the job itself.

The staves are manufactured from selected pine, fir, redwood, and cypress, free from loss knots and other defects. Wooden pipes are manufactured up to 7 metres diameter. These pipes are designed to bear minimum 11.0 kg/cm² internal pressure. The life of wooden pipes is 30-50 years and they have low friction coefficient due to which their carrying capacity is more. The carrying capacity of wooden pipes does not decrease with age.

Wooden pipes can be easily repaired; have light weight; are not damaged by corrosive water; can be cheaply and easily laid. But they leak under varying pressures, cannot bear high pressure and may collapse under heavy external loads. These pipes are not suitable for intermittent water supply system, because under such circumstances they are decayed by wet rot.

Type # 9. Plastic Pipes:

Now a days plastic pipes are becoming more and more common, due to their properties of corrosion resistant, light weight and economy. The plastic materials have their own merits, and therefore the plastic pipes have limitations and advantages for a particular application under conditions of use.

Following types of plastic pipes are available in market:

(а) Low density polyethylene pipes are flexible and this material is used up to 63 mm diameter pipes. These pipes are recommended for use in long runs e.g. for point to point conveyance of water. Due to flexibility; the LDPE pipes required supports at closer intervals for horizontal and vertical runs. These are not suitable for installation of internal water supply system.

(b) High density polyethylene pipes are tougher as compared to LDPE pipes. Pipes up to 1600 mm diameter manufactured, but in India pipes from 16 mm to 400 mm diameter are available.

Due to practical difficulties in site jointing and taking out of various connections, these pipes in small diameter are not commonly used. These pipes in large diameter for conveyance of water effluents and in long runs form point to point have been found very suitable and accepted by various P.H E. Deptts.

(c) Ployethylene pipes are normally available in black colour. These pipes are resistant to most chemical, except nitric acid, and very strong acids, fats and oils and certain solvents particular chlorinated ones. There is a phenomenon called environmental stress cracking which means that if polyethylene is stressed at normal temperatures and comes into contact with certain materials then it will crack and eventually fall. The materials include detergents, organic acids, esters, aldehydes, ketone, amides, nitro-compounds, and alcholos (but hot bear). The HDPE is worse than LDPE in this respect.

(d) Rigid (unplasticized) PVC pipes are widely used for cold water services internal/ external water supply systems, water mains, rain water system, soil waste piping system. Rigid PVC is three times as rigid as polyethylene. It is stronger and can withstand much higher pressure for a given wall thickness. Joints can be easily made in rigid PVC pipes by solvent welding, and a whole range of injection moulded matching fittings and specials are available in the market.

Rigid PVC pipes are normally available in the following shades:

(i) White/cream,

(ii) Light to dark grey, and

(iii) Black.

Generally rigid PVC is resistant to most inorganic acids, alkalines and salts, as well as many organic chemicals. It is quite resistant to most effluents, salt water and plating solutions, corrosive fumes, soils and the like which lead to its application over a wide field. This material is also safe with potable water, whether hard or soft.

With hard water, it tends to retard the formation of scale, concentrated, oxidizing acids, esters, ketones, aromatic and chlorinated hydrocarbons, organic compounds, organo-amino compounds, liquor solvents and acetic anhydride do attack the rigid PVC materials, and should be protected from them.

These pipes are designated by external diameter and shall conform to IS: 4985-1968 (revised). Tables 7.7 and 7.8 give the dimensions of rigid PVC pipes.

Type # 10. Vitrified Clay Pipes:

These are not commonly used for carrying water under pressure. These are extensively used for carrying sewage and drain water. These pipes provide smooth surface and are free from corrosion. These are manufactured in common lengths from 60 cm to 120 cm or so. These are not commonly used in conveying water.