Pipe Materials and Types of Joints

Types of pipe materials• Metallic Pipes : – Unlined metallic pipes – • Cast Iron(C.I)• Galvanized Iron(G.I)• Mild Steel(M.S)• Ductile steel (D.I)

– Metallic pipes lined with cement mortar or epoxy lining• Non metallic pipes– Reinforced Concrete, Pre-stressed Concrete, Bar

Wrapped Steel Cylinder Concrete, Asbestos Cement– Plastic pipes: PVC, Polyethylene, Glass Reinforced

Plastic, UPVC etc.

Cast Iron pipes Galvanized Iron pipes

Ductile Iron pipesMild steel pipes

Reinforced concrete pipes Asbestos cement pipes

Prestressed pipesPVC pipes

HDPEPolyethylene pipes

Bar wrapped Steel cylinder pipes

CAST IRON (C.I) PIPES• Widely used for city water supplies• Sufficiently corrosion resistant• Available in lengths of about 3.7 and 5.5m and

diameters of 50 – 900mm• Manufacturing methods:– Sand moulding • Casting in Horizontal position – “McWane” pipes• Casting in vertical position – “Pit cast pipes”

– Centrifugal process• Sand spun pipes – made in sand moulds• Delavaud pipes – made in metallic moulds

Advantages and Disadvantages of C.I pipes

• Advantages– Cost – moderate– Economical– Strong and durable– Corrosive resistant if coated– Easy to join– Resists impact without damage

• Disadvantages– Interior of pipe becomes rough with age – discharge carrying

capacity is reduced– Large dia pipes are heavy and hence uneconomical– Likely to break during transportation or jointing

GALVANIZED IRON PIPES

• GI pipes with circumferential corrugations are much more stronger than ordinary one.

• Hence they are used where large dia pipes of smaller thickness is required.

• Widely used for internal connections in buildings.

• GI pipes are not cast but made by riveting or welding steel plates

• Advantages– Cheap– Light – easy to handle and transport– Easy to join– Less Frictional losses

• Disadvantages– Life is short – 7 to 10 yrs– Easily affected by acidic and alkalic waters –

incrustations form easily inside the pipe

DUCTILE IRON PIPES

• Manufacturing process:– Addition of magnesium into molten iron of low

sulphur content– Mg causes graphite in the iron to precipitate in the

form of microscopic spheres. This improves the properties of ductile iron

– Generally manufactured by centrifugal cast process.

• DI pipes have excellent properties of– Impact resistance– High wear and tear– High tensile strength– High ductility– Corrosion resistance

• DI pipes are strong, both inner and outer surfaces are smooth.

• Diameter: 80mm to 1000mm • Length : 5.5 to 6 m

CEMENT CONCRETE PIPES

• Plain cement concrete pipes – small sizes ( dia 0.6m)• Reinforced cement concrete pipes – large sizes (dia 1.8

m upto 4.5m)• Manufacturing Methods (based on location)– Cast in-situ– Precast

• Manufacturing process of RCC pipes– Ordinary methods of concrete pouring and tamping– Centrifugal type– Cylinder type

• Mix used – 1:2:2 with max. aggregate size as 6mm• Diameter : 0.1m to 1.2m• Thickness : 2.5cm to 6.5cm• For head greater than 30m, Prestressed pipes are

used.– Laid with a welded steel cylinder to ensure water

tightness.– High tensile wire is wound around it to cause

prestressing of the core.– Concrete is laid by centrifugally.– Available in dia ranging from 80 mm to 1800 mm.

• Advantages– Inside of pipe is smooth hence friction losses are low.– Durable.– Low maintenance cost.– Life is at least 75 years.– Resist external compressive loads and do not collapse

under nominal vacuums and traffic loads.– Easy to construct at site or at factories with local

ingredients– No need of expansion joints when laid above the

ground.– If laid under water, empty pipes do not float because

of their heavy weights

• Disadvantages– Heavy and difficult to handle.– Likely to crack during transportation.– Repair work is difficult.– Likely to corrode by ground water due to the

presence of acids, alkalis or sulphur compounds.– Cannot withstand very high pressures.– Difficult to join– Tend to leak due to shrinkage cracks and porosity

VITRIFIED CLAY PIPES

• Used for carrying sewage and drainage at partial depths.

• Not used as pressure pipes for carrying waters since clay is very weak in tension and formation of watertight joints becomes difficult.

• Free from corrosion• Provide a smooth hydraulically efficient surface.• Available in lengths of about 0.6m.

ASBESTOS PIPES• Asbestos, silica and cement are converted under

pressure to a dense homogeneous material – Asbestos cement possessing high strength.

• Asbestos fiber serves as reinforcement• Diameters: 10 to 90 cm• Length : 4m• Made in 4 different grades to withstand pressure of 350

kN/m2 to 1400 kN/m2 as per IS 1592 -1989.• Used as distribution mains in India.• Can withstand pressure from 50 to 250m head of water

depending on the type and class of manufacture.

• Advantages– Light and easy to transport– Easily assembled without skilled labour– Highly corrosion resistant– Highly flexible and allows 12° deflection in laying them around

curves.– Expansion joints are not required – Used as small size distribution pipes

• Disadvantages– Costly– Not much strength, brittle and soft.– Liable to get damaged by excavation tools or during transportation

or transits.– Rubber joint seals may deteriorate if exposed to gasoline or

petroleum products.– Cannot be used for high pressure.

POLYETHYLENE PIPES • Rigid PVC and High Density PolyEthylene pipes(HDPE) – water

distribution systems • Dia ranges from 15 to 150 mm and sometimes upto 350 mm.• Advantages– HDPE pipes are rigid and tough.– These pipes can be joined with detachable joints and can be detached at

the time of shifting the pipeline.– Easily bent in installation– Eliminates the use of specials like bends, elbows etc.,– Easy to carry and install.– Lighter in weight and can be carried to heights– Has excellent free flowing properties– Non-adherent surfaces so that it rejects the foreign materials– Anti-corrosive– Friction and pressure loss is less

CLASSIFICATION OF PIPES BASED ON PRESSURE

1. Types of cast iron (spun) pipes as per IS 1536:1976

S.NoCategory of pipes in the order of increasing thickness for the same diameter

Test Pressure in kN/m2

Working Pressure in kN/m2

1 Class LA 3500 1200

2 Class A 3500 1800

3 Class B 3500 2000

2. Test Pressures in Vertically Cast Iron Pipes as per IS 1537 -1976

S.No Diameter Test pressure kN/m2 using socket and spigot joint

Class A Class B

1Upto and including 300 mm 2000 2500

2 Over 300 mm and upto and including 600 mm 2000 2500

3 Over 600 mm and upto and including 1000mm 1500 2000

4 Over 1000mm and upto 1500mm 1000 1500

3. Ordinary R.C.C pipes as per 458 - 1988

CategoryDia available (mm)

Test pressure in kN/m2

Places where used

Class P1 80 – 1200 200Used on gravity mains, design pressure not exceeding 2/3 of test pressure

Class P2 80 – 600 400Used on pumping mains, the design pressure not exceeding ½ of the test pressure

Class P3 80 – 400 600 -do-

4. Steel cylinder R.C.C pipes as per IS 1916 -1989

Category Test pressure in kN/m2 Working pressure

Class 1 500

In general, working pressure for pumping mains is taken as 50% of the test pressure; and for gravity main is taken as 2/3rd of the test pressure.

Class 2 1000

Class 3 1500

Class 4 2000

Class 5 2500

Special classAbove 2500; to be specified by purchasers

JOINTS IN PIPES• Categories of joints depending upon their capacity of

movement– Rigid joints - No movement• Flanged

– Requires perfect alignment– Close fittings are frequently used– Gaskets – compressed fiber board or natural or synthetic rubber

• Welded and turned– Produce continuous line of pipes

• Bored joints– Semi rigid joints• Spigot and socket with caulked lead joint

– Flexible joints• Comprises mechanical and rubber ring joints or tyton joints• Allows some degree of deflection – able to stand vibration and movement

Types of joints in cast iron pipes• Socket and spigot joint• Flanged joint• Mechanical joint• Flexible joint• Expansion joint

Socket and Spigot Joint• Also known as bell and spigot

joint.• Enlarged end – bell or socket• Normal end – spigot• Quantity of lead needed per

joint – 3.5 to 4 kg for 15cm dia pipe, to about 45 to 50 kg for 1.2m dia pipe.

• Somewhat flexible joint• Allows the pipes to be laid on

flat curves without any specials.

Flanged joint

• Rigid and strong • Cannot used where

deflections or vibrations are expected.

• Expensive and mostly used for indoor works – pumping stations, filter plants.

Mechanical joint or dresser coupling

• Used to join the plain ends of CI pipes

• Strong and rigid• Can withstand

vibrations - useful for pipes to be carried over bridges or below bridges in hangers.

Flexible joint

• Used where large scale flexibilities are required. – Ex: River with uneven

beds, on curves.• Socket – spherical• Spigot – plain end

having bead.

Expansion joint• Provided at suitable intervals

in the pipeline – to counteract the thermal stresses produced

• Socket end is cast flanged• Spigot end is plain• On expansion, socket end

moves forward, the gap (equal to L. α. T) just closed.

• On contraction, the socket end moves backward creating gap.

Joints in Galvanized steel pipes

• Generally, steel pipes of different lengths are connected by riveted or welded joints.

• Expansion joints are not required in steel pipes which are buried under the ground, because they are not subjected to large temperature stresses

• Pipes which are exposed to atmosphere may require expansion joints to minimise temperature stresses.

Typical expansion joint for steel pipes

Joint in Hume steel pipes

Joint in Asbestos Cement pipes – Simplex joint

Reference

• Environmental Engineering(Vol. I) – Water supply Engineering – Santhosh Kumar Garg – Khanna Publications