Maintenance of Water Supply and Drainage Systems

Factors Governing Selection of Pipes 

The broad term 'pipe'  covers a variety of tubular materials which differ in size and composition. A first hand knowledge of different pipes are useful for replacement of damaged pipe. Each lung of pipe has its purpose or is suggested as being best for a specific use. For in house plumbing work the most commonly used are cast iron, galvanized iron, galvanised steel. Polyethylene and unplasticized PVC pipes also are used now a days. Copper pipes are used particularly in hot water installations provided water is not capable of dissolving an undue amount of copper. Cast iron finds use in water pipes, soil pipes, vent pipes, sewers and traps. All these are used for fittings in water drainage and vent systems. 

Although iron and steel pipes are subject to corrosion, their strength, and versatility make them suitable for structural purposes. Polyethylene and U PVC pipes are best suited for carrying hard waters and in areas subjected to corrosion. Even for building drainage rigid PVC pipes and fittings (known as SWR pipes meaning soil, waste and rain water pipes) are becoming very popular because of their lower cost and ease of handling compared to CI Soil pipes and fittings. This also contributes for better aesthetics. 

Although air always contains oxygen, and carbonic acid, perfectly dry air will not rust iron. Moisture may invalidly be present and this may absorb the carbon dioxide, sulphur dioxide and other acidic agents from the air. These gases react with the water to form carbonic acid, sulphuric acid or other acids. Acid water tend to attack iron or steel while alkalies tend to check their rusting. 

Soft waters are more corrosive than hard water.  Soft water, such as rain water, corrodes, then washes away the corrosion and the action continues.  Waters known as temporarily hard (those containing carbonates in solution), protect the metal by depositing an insoluble coating. while permanently hard waters, (which includes sulphates) do not form a permanent coating. 

Water must contain dissolved oxygen and an acid to corrode iron. While aeration reduces the carbonic acid in water it adds dissolved oxygen which will cause rusting if any acid is present.  Saline waters are very corrosive, chiefly on account of the chloride. 

Heat increases the rate of corrosion. That's the reason why other things being equal, hot water lines become clogged before cold water lines, and cast iron water-backs produce red water and clog. It is also the reason why brass pipes are used on hot water lines, while iron or steel is used on the cold water lines to reduce initial cost. Like soft waters, hard waters also affect a plumbing system. Usually ground water sources found to be harder than surface water sources. 

The acceptable limit for hardness in drinking water is 300 mm. Beyond this limit encrustation in water supply pipes and structures is observed. Even though reduction in hardness by softening is desirable, in many instances. it is not possible to provide softening  for domestic water supply. especially for signalling communities. In such situations, use pipes instead of nonmetallic pipes for water supply is desirable,  to prevent in pipes. 

Vertical soil. drain or water supply pipes do not corrode as rapidly as horizontal lines. In general, soap and grease deposits have a tendency  to protect iron, but where these deposits are small and they decompose forging org[mic acid and this acid will attack the iron. Hypochlorite of line of bleach used to sterilize water rapidly corrodes iron. 

Cast iron resists corrosion better than wrought iron or steel. It makes a better drainage system them iron pipe and will depend on the quality of water it conveys and the soil in which it is laid. It is reported that some cast iron pipes in Paris, France have been in service since 250 years and are still in good condition. It is usually to assume the life of good cast iron pipe to be more than 50 years. 

But corrosion and the length of life of pipe are not the only considerations in choosing the kind 01  pipe. either for repair or for initial building.  Cost of pipe and fittings, ease of installation and availability are other important factors to be considered.  Still another point that sometimes must be considered is local buildings  or plumbing codes which vary from one extreme to the other. In cities the whole plumbing system must be built or repaired by a licensed plumber. This is insisted on to  safeguard the hygiene of the entire community as a cross connection between the protected water supply system [and the waste-water disposal system is possible due to bad plumbing. It is therefore necessary that all works relating to plumbing within and outside the premises are properly executed under the supervision of the authorities at all stages.