Various types of pipelines

Pipelines vary mostly by the material they are built from; steel, cast iron, cement,

polyethylene.

Indeed, the material dictates for instance:

- the diameter and pressure,

- the weight and the length of the components to be joined

- how to make curves and take-offs,

- the trench preparation,

- the lowering-in technique,

- the backfilling,

- the anti-corrosion system,

- the testing.

Obviously, the environment will dictate the material:

- high pressure + big diameter will require steel,

- low pressure + big diameter will be concrete of cast iron,

- Small diameters can be any of those and also accept polyethylene (HDPE) and ABS.

This guideline deals with welded steel pipelines for the long distance transportation of:

- liquid hydrocarbons such as crude oil or refined products (diesel, gasoline, jet fuel,…),

- gaseous hydrocarbons such as natural gas (methane) or refined products (ethylene,

propane, etc…)

- water (drinking, raw or sea)

- slurry (a mixture of water and coal or ore powder)

 

Pipeline Components

A pipeline is not just an assembly of pipe joints welded together. It is a system that constitute

a functional transportation system, like a road or railway network.

Many fittings, accessories and facilities are installed on a line for the operations of this

transportation equipment:

- flanges, bolts, gaskets, casings,

- valves, vents, relief devices,

- thrust blocks

- cleaning facilities: scrapper traps or pig traps,

- metering stations,

- compressor or pumping stations

- cathodic protection, insulating joints,

- line markers,

- monitoring and metering stations

 

Pipes

Pipelines can measure anywhere from 6 to 60 inches in diameter, although certain component pipe sections can consist of small diameter pipe, as small as 0.5 inches in diameter. However, this small diameter pipe is usually used only in gathering and distribution systems.

Mainline pipes, the principle pipeline in a given system, are usually between 16 and 48 inches in diameter. Lateral pipelines, which deliver product to or from the mainline, are typically between 6 and 16 inches in diameter. Most major interstate pipelines are between 24 and 36 inches in diameter. Pipelines are produced in steel mills, which are sometimes specialized to produce only

pipeline. There are two different production techniques, one for small diameter pipes and one

for large diameter pipes. For large diameter pipes, from 20 to 60 inches in diameter, the pipes

are produced from sheets of metal which are folded or rolled (spiral) into a tube shape, with

the ends welded together to form a pipe section. Small diameter pipe, on the other hand, can

be produced seamlessly. This involves heating a metal bar to very high temperatures, then

punching a hole through the middle of the bar to produce a hollow tube. In either case, the

pipe is 100% tested before being shipped from the steel mill, to ensure that it can meet the

pressure and strength standards for transporting natural gas. Line pipe is also covered with a specialized coating to ensure that it does not corrode once placed in the ground. The purpose of the coating is to protect the pipe from moisture, which causes corrosion and rusting. Coating can also be applied on the inside of the pipes to protect them against corrosion and to reduce the friction loss. There are a number of different coating techniques. In the past, pipelines were coated with a specialized coal tar enamel. Today, pipes are often protected with what is known as a fusion bond epoxy, which gives the pipe a noticeable light blue colour. 

In addition, as the coating is never totally perfect and will deteriorate with time, cathodic

protection is often used. This is a technique of running an electric current through the pipe to

ward off corrosion and rusting.

 

Valves

International pipelines include a great number of valves along their entire length. These valves work like gateways; they are usually open and allow the product to flow freely, or they can be used to stop the flow along a certain section of pipe. There are many reasons why a pipeline may need to restrict flow in certain areas. For example, if a section of pipe requires replacement or maintenance, valves on either end of that section of pipe can be closed to allow engineers and work crews safe access. Some valves are equipped with actuator that can be triggered by a sudden drop of pressure resulting from a major leak. These large valves can be placed every 10 to 30 km along the pipeline, and are subject to regulation by safety codes.