The pipeline is the arrangement of the closed conduit to flow and transport any fluid (both gas and liquid) from one destined place to another with a minimum amount of loss. Different types of pipelines are used for a different purpose.
Both pressure flow and non-pressurized flow can be achieved in pipelines. The pipe is generally made of cylindrical shapes as they have optimal hydraulic and mechanical efficiency.
Generally, two-three types of stress, i.e. longitudinal, radial and hoop stress are created in a (thin thickness) pipeline. Thus they are designed according to this so that they can withstand the pressure created by the flowing liquid.
The inner surface of a pipeline is responsible for hydraulic efficiency. Sometimes for hydraulic efficiency and other purposes, the pipelines are of oval or other cross-section. This is generally adopted for the non-pressure flow in the sewer system.
Most of the pipeline also had to withstand the external pressure or a load of backfilling and hill outcrops.
Thus different types of the pipeline are available accordingly to their use, location to be used, exposure conditions, hydraulic efficiency and structural design requirements.
Moreover, the selection of type pipeline also depends upon ease in construction, joint mechanism of pipes, serviceability and durability and their maintenance.
Types of pipelines
A) On basis of material of construction
1) Steel pipeline
These pipes are generally used for water transport as well as gasoline liquid transport flowing at high pressure. They have an extremely large diameter and can be of very long extension in length.
They are basically adopted for hydropower water conveyance system as headrace pipe. They can withstand a large amount of pressure and also doesn’t get rusted.
They are fabricated by rolling the mild steel plates and joined by riveting or welding. However, they can’t withstand high external pressure. The welded steel pipe can be made up to 2.4 m in diameter and 12 m in length.
2) Cast iron (C.I.) pipes
These types of pipelines pipes are relatively thicker than steel pipe and are not much larger in diameter compared to steel pipeline. They are generally manufactured from cast iron and cast with the inner lining synthetic polymer fibre for better hydraulic efficiency and resistance against corrosion.
Moreover, they are painted outside in order to prevent rusting. They are very durable and have a life span of 100 years. However, these pipes are heavy and brittle to handle. These pipes can be joined by the bell and spigot joint, threaded or flanged joints.
They are used for water transmission but of lesser discharge like water supply scheme for town or city. Also, they are popularly used for the transmission of sewage and gases.
3) Galvanized iron pipes(G. I.)
These are also. Mild steel or Wrought iron pipes but with a protective layer of zinc on both inner and outer surface. These pipelines are generally used for house pumping and after service connection in the home.
Their life span is 20 years. They are sensitive to acidic or alkaline water which leads to early corrosion. But they are cheap and easy to handle for the general household pipelines.
4) Plastic pipelines
They are the cheapest and alternative method of pipeline construction. Moreover, they have high resistance against corrosion, abrasion and chemical attacks.
The only drawbacks are it cannot withstand a large amount of pressure, are susceptible to temperature and are not eco friendly. Thus they are used for low-pressure fluid transport like normal sanitary and water supplies works, gaseous transport, etc.
They are generally weak so, heavier loads are not allowed over them. Their lightweight and easy joining techniques make them very familiar and high demand in use.
Different types of synthetic polymer plastic have been developed which are used accordingly to need. Some the examples are;
Polyvinyl Chloride pipes (PVC): These pipes are rigid, strong in resisting pressure, easy to join and light in weight and can withstand temperature up to 60°C. So they are adopted popularly for indoor sanitary pipelines.
Polypropylene Random copolymer pipes (PPR): These pipes have multi-layers of synthetic plastic. They can withstand temperature up to 70°C so, can be used to hot water supply too.
They are highly used for drinking water transport. They are an excellent alternative for GI pipes. For drinking purpose, they are generally available from 10mm to 75mm.
HDPE (High-density polyethene) pipes: These are pipe which can withstand relatively high pressure both internally and externally. So used when the pipe is needed to be laid on the high-pressure zone (like beneath road) for drinking water transmission and sometimes gaseous transmission too.
5) Concrete pipeline
These types of pipelines pipeline is made of reinforced or plain concrete. The circular stirrups and longitudinal bars are used and cast with concrete. They can withstand a large amount of external and internal forces.
PCC pipeline is used for head up to 7m, RCC pipeline for heads up to 60m and if higher heads than that are required then pre-stressed concrete pipeline are used. So the places where there is a large amount of external force they are preferred. They are generally used for drainage system beneath the road, for culverts etc.
Precast Concrete pipes are also popularly known as Hume pipes. Different types of home pipes named NP2, NP3 and NP4 are available accordingly to their strengths and surface finish in Nepal and India.
B) On the basis of purpose
1) Water supply pipeline
These pipelines are solely used for the supply of drinking water directly from the reservoir or inlet opening of the reservoir.
The pipeline diameter gets reduced as it gets distributed to a different branch. In such pipeline, different kind of valves is arranged at different locations for control of water discharge.
2) Sanitary pipeline
These pipelines are also called sewer system. In such pipeline normally, non pressurized open flow is created. Here, the pipe doesn’t need to be structurally strong to withstand internal pressure.
But rather they need to be hydraulically efficient for the flow. So different shapes of sewer-like oval horseshoe-shaped, parabolic are created.
3) Petroleum and gas pipeline
Mild steel pipes were used during the 1940s and then replaced by HDPE in the 1970s. The pipeline used these days are made of steel along with external coating and cathodic protection.
This pipeline must be leakproof so they are preferred to be joined by welding rather than the use of bolts and joints. And the flexible plastic pipe is also popularly used for the distribution of gasoline to houses from definite points.
This pipeline must need to be cleaned regularly as the oily and greasy residue stuck in pipelines. The process of cleaning is called “pigging” and the mechanical brush used to clean inside the pipe is called “Pig”.
4) Conveyance in hydropower (Penstock and headrace pipeline)
Penstock and headrace pipeline are usually of larger diameter, the only difference is their thickness and supports, made up of steel (rarely concrete) which is used for conveying water from reservoir or forebay or surge tank to the turbine unit.
They must be designed as the high-pressure pipeline and withstand static and water hammering pressure created during a sudden change in power demand (closer and opening of valves). They are usually a very expensive part of the entire hydropower project.
C) On basis of functions
1) Transmission pipeline
The conveyance of fluid through the conduit from intake to treatment plant and treatment plant to the reservoir is called transmission pipeline. This transmission pipeline sometimes transports fluid from one station to another in the case of gas and petroleum plants.
2) Distribution pipeline
These pipelines, the main purpose is to distribute the fluid or gas from the main station r reservoir to the utilizers o consumers. The distribution pipe diameter ranges from ½ inch to 6 inches. The distribution pipeline is arranged in different layout systems.
- Dead end/tree system
- Iron grid system
- Circular or ring system
- Radial system
- Collection pipeline
These Types of pipelines are used to collect fluid from different sources to intake part. In the case of oil and gasoline products, the fluid is pumped out from underneath the surface and then collected.
For water, there is the more popular use of open channel rather than pipeline as sedimentation of heavier particles cause problems.
I hope this article on “Types of pipelines” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rajan Shrestha