The following points should be kept in mind while selecting pipe for a certain water supply system,

• Carrying capacity.
• Durability.
• Fire cost.
• Maintenance cost.
• Type of water to be conveyed.

1 - Cast Iron Pipes (C.I)

• Most widely used for the city water supplies.
• Average life is 100 years.
• Corrosion my reduce its capacity by 70%.
• Must be lined with cement or bitumen.
• C = 130 for new pipe.
• C = 100 for old pipe (Selected for Design).

"C" is the Hazen Williams Coefficient known as HWC. It is the important term used in the design of water distribution system.

2 - Steel Pipes

• Contains less carbon than Cast Iron pipes.
• Frequently used for trunk mains.
• Difficult to make connections hence seldom used for water distribution systems.
• Much Stronger and lighter than Cast Iron pipes.
• Cheaper than Cast Iron pipes.
• Cannot withstand vacuum, hence collapse.
• Highly susceptible to corrosion, hence high maintenance charges are required.

3 - Ductile Pipes

• Similar to Cast Iron pipes except increased ductility.
• Ductile iron is produced by adding a controlled amount of Mg into molten iron of low sulphur and phosphorous content.
• Stronger, tougher and elastic than Cast Iron pipes.
• More expensive than Cast Iron pipes.

4 - Galvanized Iron (G.I) Pipes

• Manufactured by dipping Cast Iron pipe in molten zinc.
• Resistant to corrosion.
• Mainly used for plumbing.

5 - Concrete Pipes

• Usual size of Reinforced Cement Concrete pipe is 400mm dia. and above.
• Not subjected to corrosion.
• Manufactured at or near site.
• Average life is 75 years.
• C = 138 to 152.

6 - Asbestos Cement Pipes (A.C)

• Sizes are 100mm to 600mm dia.
• Average life is 30 years.
• Immune to actions of acids, salts, soil and corrosion.
• Less cost for laying and jointing.
• Less plumbing cost due to less friction.
• C = 140.

Asbestos Cement pipes are economical and are generally preferred to use in the design of water supply systems.

7 - Poly Vinyl Chloride Pipes (PVC)

• Mainly used for domestic plumbing.
• Easy to install and easy to handle.
• Cheaper in material cost
• Weak to sustain load.
• Only available 350mm dia size.
• Expected life is 25 years.

What is D-class pipes?

Not sure about D-class pipes, but in sewerage system A, B and C are letters representing wall thickness of RCC pipes used.

A (Min. t), B (Medium t) and C (Max. t). These letters are used with 5 available classes (1-Class being weakest to 5-Class being strongest). e.g normally RCC pipes of Class II with wall thickness B are used. This is the correct way of describing pipe category.