Laying and Jointing of Asbestos Cement Pressure Pipe

Reading time: 1 minute

Asbestos cement pressure pipe is used for the transmission of water under pressure. It contains asbestos fiber instead of reinforcing steel, making the pipes lighter in weight and providing adequate strength.

Asbestos cement pressure pipes have good resistance to hydrogen sulfide corrosion and aggressive soils. They have low operating costs as the smooth walls of the pipe impart low friction factors.

 The other three types of asbestos cement pipes are:

1. Non-pressure pipes for sanitary sewers
2. Storm drain pipes for carrying storm drains
3. Transmission pipes for use as water mains

1. Storage of Asbestos Cement Pipes

1. The stack shall be in a pyramid shape, or the pipes laid lengthwise and crosswise in alternate layers.
2. The pyramid stack is advisable for smaller diameter pipes to conserve the space required to store.
3. The height of the pipe stacks shall not exceed 1.5 m.
4. Cast iron detachable fittings and joints shall be stacked under cover and separated from the asbestos cement pipes and fittings.
5. Rubber rings shall be kept clean and away from grease, heat, oil, and light.

2. Trenches for Laying Asbestos Cement Pipes

1. The width of the trench above the pipe level shall be as small as possible but shall provide sufficient space necessary for joining the pipes.
2. The trench width shall be to provide a space of 300 mm on either side of the pipe.
3. The pipes shall have a minimum soil cover of 750 mm when laid under footpaths and sidewalks, 900 mm, when laid under roads with light traffic, and 1.25 m when laid under roads with heavy traffic.
4. When the soil has a poor bearing capacity and is subjected to heavy traffic, the pipes shall be laid on a concrete cradle.
5. An extra trench depth of 100 mm shall be provided for each jointing pit.

3. Jointing of Asbestos Cement Pipes

Before commencing jointing, the pipes, joints, and ends of the pipes shall be cleaned with a hard wire brush to remove all the loose particles.

3.1 Cast Iron Detachable Joints

1. The joint shall consist of a central collar, two rubber rings, two flanges of cast iron, and the required number of bolts and nuts, as shown in Figure 1. 
2. One flange and rubber ring shall be placed on the end of the pipe already laid, and the other flange, rings, and central collar shall be slipped onto the pipe to be assembled.
3. The rubber ring shall be positioned at half the collar width from the end of the pipe already laid.
4. The other pipe shall be brought nearer, leaving a gap of 5 mm between the two pipe ends.
5. This gap will facilitate maneuvering of deflection at joints after assembly and will take care of expansion in the pipeline.
6. The collar shall be slid to sit square around the rubber ring to pipe no. 1, and the rubber ring shall be rolled on pipe 2 to sit around the collar.
7. The flanges shall be moved on both ends to enclose rubber rings.
8. The fastening bolts shall be inserted through the holes of the flanges, and the bolts shall be tightened alternately and evenly for proper sitting of the joint.

3.2 Asbestos Cement Coupling

1. This joint shall consist of three rubber rings and an asbestos cement coupling machined inside.
2. The rubber rings shall be seated in respective grooves after cleaning the coupling and rubber rings.
3. The machined ends of the pipe cleaning the coupling shall be suitably lubricated, which is not detrimental to rubber rings or drinking water.
4. The assembly shall be made by pushing with a crowbar (as shown in Figure 2 ) or using a pipe puller.
5. The joints shall be made by keeping the pipes in one line.
6. Any permissible deflection at the joint shall be made after completing the joint only.
7. Wherever necessary, change over from cast iron pipe to asbestos cement pipes, and vice versa shall be done with the help of a suitable adapter shown in Figure 2.

4. Laying of Fittings

Normally, when a pipeline is laid, a certain number of cast iron fittings such as tees, bends, reducers, and special fittings such as air or sluice valves are required.

1. All cast iron fittings shall be plain-ended to suit the class and diameter of the pipe manufactured.
2. Cast iron fittings are jointed by cast-iron detachable joints only.
3. Cast iron specials having flanges are jointed in the pipeline, with cast iron flange adapters having one end flanged and the other plain ended.

5. Anchorages for Asbestos Cement Pipe

Care shall be taken while joining cast iron pipes, as the joints do not hold the pipe ends firmly. During working or testing pressure, there will be the tendency for the pipe ends or specials ends to slip out the joint, more so in case of a blank end cap used for closure of pipeline and in case of degree bends and tees. 

In order to keep them firmly in the pipeline, anchoring these pipe ends and special ends is necessary against the direction of thrust. 

1. The anchorage shall consist of either concrete cast-in-situ or masonry built-in cement mortar.
2. The anchors shall be extended to the firm soil of the trench side.
3. The shape of the anchors will depend on the kind of specials used. 
4. They shall be spread to the full width of the trench and carried vertically by the side and over the special to about 15 cm.
5. The bearing area on the sides of the trench shall be proportional to the thrust and the bearing capacity of the sides of the trench.

FAQs

Read More

How to Install Reinforced Concrete Pipe (RCP)?

How to Lay and Join Stoneware Pipes?

What are the Important Types of Pipe Appurtenances?