Hydraulically activated pipeline pigging (HAPP) is a pigging technology applied for pipeline cleaning. The basic principle is that a pressure drop is created over a by-passable pig hold back against a pipeline’s fluid flow. The pipeline fluid passing through the pigs cleaning head is accelerated by this pressure drop forming strong cleaning jets. These jets are directed onto the inner wall in front of the pig removing all kind of deposits. Generally this technology transforms kinetic energy of the pipeline fluid into a locally available differential pressure which in this case is used to create cleaning jets but can also be used otherwise.
Pigs used today can be divided into three categories (Fig. 2):
Generally for cleaning pigs, the cleaning force applied is the mechanical force between the pipe inner wall and the cleaning pig itself. This force is determined by the pig travel speed as well as by the hardness and shape of the cleaning edge: The faster the pig, the higher the cleaning impact on the deposits but at the same time only the surface of debris is scratched away. Therefore several, sometimes quite many, pig runs are required to clean a pipeline.
Hydraulic activated pigs apply high pressure liquid jets either supplied by high pressure hoses (depended) or made available by the kinetic energy locally available. Depended hydraulic activated pigs are limited in reach due to the hose which needs to be inserted into the pipeline and guides the cleaning head.
All units have openings that allow the entire fluid flow through the pipeline to bypass. The brake unit ensures that a hydraulically activated pig is held back against the fluid flow in the pipeline. The fluid pushes against the following seal unit, which channels it into the openings of the cleaning head. Seal unit and cleaning head pose a flow restriction resulting in a pressure difference across the pig. Thus the fluid is accelerated in the cleaning head's nozzles creating extremely powerful liquid jets. These jets are directed onto the pipe inner wall and remove any kind of deposits.
The brake unit ensures that the travel speed of the pig is many times slower than the fluid velocity thus allowing it to entirely remove deposits from the pipe wall before it travels across the cleaned surface. The deposits removed are immediately flushed downstream the pipeline with the main jet of the cleaning head which is directed in the middle of the pipeline. With all deposits removed from the pipe wall and transported downstream by the fluid flow there remains no risk of the pig getting stuck in debris accumulated in front of it.
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