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1.6 Water Conveyance

1.6.1 Water Conveyance by Pipelines

Humans have used pipelines for water conveyance throughout the ages. However, the materials used in manufacturing pipelines, as well as knowledge of the properties and manufacturing these materials, has improved over time. Originally made of such materials as burned mud and clay, they are now made of such materials as iron, concrete, plastic and fiberglass.

Pipelines are used throughout the countries of the West Asia region in all types of water projects, including water, irrigation, various industries and sanitary drainage projects.

Technology Description

Water pipelines are laid in trenches excavated along the pipeline route, and subsequently backfilled with soil after the pipeline is installed. Pipelines typically consist of pipes (joints) and special parts (fittings), joined together by several methods on the basis of the pipeline material. The water pipes used in the region can be separated into eight different categories, as described in the following sections.

Reinforced Concrete Pipes

Reinforced concrete pipes were first manufactured in 1894, and they are still used to convey potable and irrigation water. Two types of these pipes are currently used, including:

• Concrete reinforced with a steel cylinder, with steel bars spirally- coiled around the cylinder;
• Concrete reinforced with a steel cylinder and spiral bars, as well as straight prestressed bars.

The steel cylinders ensure the water tightness of the pipe. The pipes are joined together through fittings with rubber seals to ensure no water leakage at the joints.

Advantages of the reinforced concrete pipes are as follows:

• Suitable for conveying all types of water;
• Easy to install and with flexible joints;
• Can withstand backfill pressure, as well as vehicle traffic loads taking place above it;
• Because of the smooth inner surface, there are small friction losses;
• They are available in different diameters ranging (300-1,500 m for the first type of pipe; 1,000-4,000 mm for the second type);
• They are water tight and durable, even with cracks in the inner and outer coating layers;

The disadvantages of reinforced concrete pipes are as follows:

• It is necessary to conduct detailed studies regarding the pipe fittings, based on the specific project requirements;
• They are heavy, with this feature being reflected in their transportation and installation costs;
• It is difficult to re-establish the inner and outer pipe coating if it is damaged during repair works;
• They require special care in its manufacturing, transportation and installation;
• They may require grounding measures in some cases.

Asbestos-Cement Pipes

These pipes have been in use throughout the world since 1913. They are made of a mixture of 82-90% cement and 10-18% asbestos fibers. They are available in diameters ranging between 60-2,000 mm, and can withstand pressures ranging between 6-20 atmospheric pressures.

These pipes are connected with separate special fittings. The use of asbestos pipes to convey potable water over the last two decades, due to increasing concern with their health hazards. However, they are still used to convey irrigation and sanitary drainage water.

The advantages of asbestos pipes are as follows:

• They are resistant to wear and corrosion, thereby being useful in situations involving corrosive water or soil;
• They have smooth internal surfaces, resulting in low friction losses;
• They are easy to install and maintain;
• The major raw material (cement) required for their manufacture is usually available locally.

The disadvantages of asbestos pipes are as follows:

• The asbestos material used in manufacturing the pipes represent a carcinogenic health hazard when used to transport water for human consumption. It also is a hazard during the manufacturing, installation and maintenance of the pipes;
• The pipes have a low resistance to vibrations from vehicular traffic passing over them;
• They have a low resistance to shocks, facilitating their breakdown during their loading, transportation, unloading and installation;
• It is difficult to secure precise measurements of the thickness of the cylinder during the manufacturing process, as well as difficult to determine the required resistance to pressures;
• There is a poor availability of fitting of the same material as the cylinder;
• They cannot be used in loamy soil that expands, or in liquid soils.

Steel Pipes

The most popular steel pipes used to convey water are black steel pipes and galvanized steel pipes. Steel pipes are manufactured by longitudinal or spiral welding, or by soldering. They can be used without outer layer protection in visible places, in places where it is covered with concrete, or protected with a polyethylene layer or cement mortar lining.

Steel pipes are widely used in all the Arab countries of West Asia to convey water, primarily because of their availability in a wide range of diameters (6-2,500 mm). They also are easily connected with welding, flanges or threading (for relatively small diameters).

The advantages of steel pipes are follows:

• They are resistant to high pressures;
• They are easy to connect, install, operate and maintain;
• They are ideal for extension work in reservoirs and pumping stations, and at riverbanks and steep-slope crossings;
• They can withstand shocks and traffic vibrations.

The disadvantages of steel pipes are as follows:

• The internal and external coatings are susceptible to welding damage during installation;
• They are susceptible to wear and corrosion in sub-surface lines, reducing their lifespan compared to other types of pipes;
• They have low resistance to acidic or highly-salinity soils;
• They require grounding measures.

Ductile Iron Pipes

Ductile iron pipes are made of cast iron to which magnesium has been added to give it flexibility. They are widely used for potable water supply projects, with diameters generally ranging between 60-2,000 mm or even larger. Ductile steel pipes are lined with cement mortar on the inside, and zinc and bitumen on the outside. There are few available methods for connecting the pipes, requiring fittings of appropriate diameters.

Ductile steel pipes are used in all the Arab countries of West Asia to convey potable water from water sources to distribution tanks and through the potable water distribution pipeline networks.

The advantages of these pipes are as follows:

• They have high resistance to rust, corrosion and shocks;
• They can withstand high working pressures;
• They have smooth internal surface, reducing their friction losses;
• The needed fittings are available in the same material as the pipes;
• They are suitable for potable water conveyance;
• They are easily installed and maintained, and have a high sustainability.

The disadvantages of ductile steel pipes are as follows:

• Pipes with diameters exceeding 1,000 m are very expensive, since they require special technology only available with a few manufacturers;
• They require a protective polyethylene casing in areas with corrosive soils.

Prestressed Concrete Pipes

These pipes are made of concrete, reinforced longitudinally and transversely with prestressed reinforcement bars. The prestressed bars give the pipes the advantage of high resistance to internal and external pressures.

Prestressed concrete pipes had been used since 1937, and are available in diameters ranging between 300-2,000 mm. They require a two-stage manufacturing process. In the first stage, the prestressed steel is placed in molds in which concrete is poured, using a centrifugal method to ensure high-quality concrete. In the second stage, an external layer of prestressed steel is rolled around the hardened cylinder, and another layer of concrete is then poured over it to cover the steel. The pipe fittings are made in the same manner as the pipe.

The advantages of prestressed reinforced concrete pipes are as follows:

• They are resistant to rust and corrosion;
• Because the steel is covered with concrete, there is no need for grounding measures;
• They can withstand backfill pressure and static loads;
• It is possible to construct manufacturing factories locally or within the proximity of the site at which they will be used, reducing transportation costs.

The disadvantages of these pipes are as follows:

• They have a heavy weight and high transportation costs;
• They are difficult to install and maintain;
• It is difficult to implement diversions after their installation;
• Manufacturing the pipes requires high precision;
• They are subject to leakage under high water pressures.

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