How GAS PIPELINES and Compressor Plants work, maintenance with Smart Pig

0:00 Intro
0:26 Natural Gas Pipelines
2:31 Compressor Station
3:02 Compressor
4:18 Pipelines
4:40 Maintenance with PIG

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In our previous videos, we have seen how gas is extracted, and how it is transported by gas carriers using liquefaction and regasification processes.

In this video, we will see what gas pipelines are; ducts used to transport natural (or artificial) gas from the production facility to consumers.

When natural gas is extracted from the reservoirs (and treated to remove substances that can give it negative characteristics for transport, distribution, quality and safety), it has to be inserted into pipelines, which are successions of steel pipes.

The total length of pipelines around the world amounts to approximately one million kilometres or 622.000 miles, more than 25 times the circumference of the Earth, and most of them are gas pipelines for the transport of natural gas, consisting primarily of methane, in fact they are also called methane pipelines.

Before choosing where to place the pipeline, in-depth geological studies are carried out to try to follow the geology of the ground or seabed, in order not to subject the pipeline to risks due to earthquakes, landslides, sea currents, excessively high pressures due to the depth, ice, changing temperatures, etc.. So as to preserve the structure over the decades, but also to safeguard the environment because methane, when dispersed in the atmosphere, is a gas which causes the greenhouse effect dozens of times more than carbon dioxide.

The initial diameter of a pipeline can be as much as 1,400 millimetres or 55 inches and then it becomes tighter gradually.
Their inner surface is polished so as to have a low internal friction coefficient as the gas passes through, while externally they are covered with a special anti-corrosion and shock-resistant coating.

Pipelines are very resistant, in fact gas can be transported by compressing it up to 70 bar in the case of land pipelines, and up to 100 bar in the case of submarine pipelines. These process is obtained by special machines called compressors.

The gas is moved in an gaseous state (unlike LNG ships that transport LNG i.e. liquefied natural gas at -163 degrees Celsius or -261 Fahrenheit) and it is pushed by a compressor station at the beginning of the pipeline, and if necessary, also by several intermediate compressor.

These are important structures, both in size and complexity, consisting essentially of gas turbines driving centrifugal compressors.

The gas turbine is an internal combustion engine that uses part of the extracted methane as fuel.
It is initially composed by an axial compressor, it includes rotors (blades that rotate together with the shaft) and stators (vane discs fixed to the frame). They create various stages, which gradually increase the pressure of the incoming air.

In the combustion chamber, the methane is added to the air, and the mixture burns.

The large expansion of hot gases that is generated make the two turbines to turn, one connected to the compressor shaft to turn its rotors;
And another, separated on a second shaft, now runs a multi-stage centrifugal compressor connected to the pipeline.
The multistage centrifugal compressor is a turbo-machine where several bladed disks called impellers, placed in rapid rotation, supply energy to the gas, which increases its pressure due to the centrifugal force.
In this way, the methane is pushed into the pipeline and can begin its journey.

Pipelines are usually placed at ground level in desert and sandy areas or where the ground is too hard to dig because of ice; or they are placed on the seabed, in this case they are called submarine pipelines. In urban areas on the other hand, they are buried about one metre deep (3 ft) below the surface

Pipelines must be constantly monitored and protected, and that is why maintenance is very important.
The most common phenomena that can occur are corrosion and build-up of deposits, which can cause pipeline deterioration and reduced flow velocity. To ensure the pipeline integrity, cleaning pigs are used to remove deposits, and then smart pigs with smart sensors are used to inspect the interior of the pipeline to detect defects.