1. General
This specification covers the material, manufacturing, testing, and quality assurance requirements for Ductile Iron (DI) pipes and fittings intended for use in pressurized water and wastewater mains. The pipes shall be centrifugally cast and shall have a high tensile strength, ductility, and resistance to corrosion, suitable for conveying water under pressure. All work and materials shall conform to the latest edition of IS 8329:2018 (Ductile iron pressure pipes for water, gas and sewage) and other relevant standards such as IS 5531:2009 (Ductile Iron Fittings for Pressure Pipes), ISO 2531:2009 (Ductile iron pipes, fittings, accessories and their joints for water applications), and ISO 8179 (Ductile iron pipes - External zinc coating).
2. Materials and Production
2.1 Ductile Iron:
The pipes shall be manufactured from spheroidal graphite (SG) cast iron, commonly known as ductile iron. The raw materials used shall be of high quality to produce iron with a graphitic structure that is predominantly spheroidal, ensuring the required mechanical properties. The chemical composition shall be controlled to achieve the specified properties and to prevent the presence of harmful elements.
2.2 Manufacturing Process:
- Centrifugal Casting: The pipes shall be manufactured by the centrifugal casting process, which ensures a dense, uniform, and concentric wall thickness. The iron shall be cast in a metal mold or a sand-lined mold.
- Annealing: Following casting, the pipes shall be heat-treated (annealed) in a furnace to transform the as-cast iron structure into the desired ferritic-pearlitic matrix. This annealing process is crucial for achieving the required ductility and toughness.
- Machining: The spigot end (plain end) and the socket end (bell) of each pipe shall be machined to precise dimensions to ensure a proper fit and a secure joint.
2.3 Mechanical Properties:
The finished ductile iron pipes shall possess the following mechanical properties, as verified through standard testing:
- Tensile Strength: Minimum 420 MPa.
- Proof Stress (0.2%): Minimum 300 MPa.
- Elongation at Fracture: Minimum 10%.
- Hardness: Shall not exceed 230 HB (Brinell Hardness).
3. Pipe and Joint Classification
3.1 Class of Pipe:
The pipes shall be supplied in different classes (e.g., K9, K12) as per IS 8329:2018 or ISO 2531:2009, based on their nominal wall thickness and intended working pressure. The class of pipe shall be clearly specified for each diameter.
3.2 Jointing System:
The pipes shall be provided with push-on type joints with an elastomeric gasket. The joint shall be capable of accommodating angular deflection and linear expansion/contraction without leakage. The joint design shall be as specified (e.g., Tyton, push-on) and shall comply with the relevant sections of IS 8329:2018.
4. Corrosion Protection and Linings
4.1 External Coating:
The external surface of the pipes shall be protected against corrosion by a layer of metallic zinc, applied by a process such as thermal zinc spray, followed by a finishing coat. The zinc coating mass shall be not less than 200 grams per square meter (g/m2). The finishing coat shall be a suitable bituminous paint or synthetic resin, with a minimum thickness of 70 micrometers (µm).
4.2 Internal Lining:
The internal surface of the pipes shall be lined with a suitable material to prevent corrosion and maintain water quality.
- Cement-Mortar Lining: The standard internal lining shall be a cement-mortar lining, applied centrifugally, conforming to IS 8329:2018 and ISO 4179:2005. The lining shall be smooth, dense, and free from cracks or voids.
- Special Linings: For aggressive waters or specific applications, special linings such as high-alumina cement, epoxy, or polyurethane may be specified.
5. Dimensions and Tolerances
The dimensions, including nominal bore, wall thickness, length, and socket and spigot dimensions, shall conform strictly to the tables provided in IS 8329:2018. Tolerances on dimensions shall be as specified in the standard. The standard length of the pipes shall be as specified in the standard, unless otherwise noted.
6. Testing and Quality Control
Each pipe shall be subjected to a hydrostatic pressure test at the factory to a pressure not less than 1.5 times the nominal working pressure or as specified in the standard. There shall be no leakage, sweating, or other signs of failure.
6.2 Mechanical Tests:
Representative samples from each batch of pipes shall be tested for tensile strength, elongation, and hardness to ensure compliance with the specified mechanical properties.
6.3 Coating and Lining Tests:
The thickness and integrity of the external zinc coating and the internal cement-mortar lining shall be checked through visual inspection and measurement. The lining shall be tested for soundness and adhesion.
6.4 Dimensions:
The dimensions of the pipes and fittings shall be checked to ensure they are within the specified tolerances.
7. Marking and Identification
Each pipe shall be clearly and permanently marked on its exterior with the following information:
- Manufacturer's name or trademark.
- Nominal diameter in millimeters (mm).
- Class of pipe (e.g., K9).
- The year of manufacture.
- The mark of the certifying authority (e.g., ISI mark).
8. Fittings and Accessories
All fittings (e.g., bends, tees, reducers) shall be made of ductile iron and shall conform to the relevant standards (e.g., IS 5531:2009). The fittings shall have the same internal and external protection as the pipes. The jointing gaskets shall be made of a suitable elastomeric material (e.g., EPDM) and shall conform to IS 5382:1985.
9. Measurement
Measurement shall be on a linear basis in running meters (m) for pipes and on a per-unit basis for fittings, as laid and jointed in position. The measurement shall be taken along the center line of the pipeline. The cost of all accessories, gaskets, and jointing materials shall be considered incidental to the cost of the pipes and fittings unless specifically itemized.
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