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 pipes Mild steel pipes

Reinforced concrete pipesAsbestos cement pipes Prestressed pipes PVC 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/m 2 to 1400 kN/m 2 as per IS 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.No Category of pipes in the order of increasing thickness for the same diameter Test Pressure in kN/m 2 Working Pressure in kN/m 2 1Class LA Class A Class B

2. Test Pressures in Vertically Cast Iron Pipes as per IS S.NoDiameter Test pressure kN/m 2 using socket and spigot joint Class AClass B 1 Upto and including 300 mm Over 300 mm and upto and including 600 mm Over 600 mm and upto and including 1000mm Over 1000mm and upto 1500mm

3. Ordinary R.C.C pipes as per Category Dia available (mm) Test pressure in kN/m 2 Places where used Class P 1 80 – Used on gravity mains, design pressure not exceeding 2/3 of test pressure Class P 2 80 – Used on pumping mains, the design pressure not exceeding ½ of the test pressure Class P 3 80 – do-

4. Steel cylinder R.C.C pipes as per IS Category Test pressure in kN/m 2 Working pressure Class 1500 In general, working pressure for pumping mains is taken as 50% of the test pressure; and for gravity main is taken as 2/3 rd of the test pressure. Class Class Class Class Special class Above 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