What is pigging?
Pigging is the process used to clean large pipelines during maintenance and installation, using devices called as ‘Pig’ which is inserted into a pipeline and which travels freely through it, driven by the product flow.
Early purpose-built mechanical pigs were made without any consideration of possible damage to tlie pipeline and comprised Iiardened steel scraper blades, steel spur wheels and leather driving cups.
Use of the correct type of pig and a proper pigging program will help to maintain the integnty and optimum efficiency of the pipeline
Why Pig a Pipeline?
Pigging helps to maintain continuous operation by:
removing any substance which might damage the pipeline process systems
They provide maximum efficiency by monitoring the operating and/or physical conditions of the line.
helping to prevent the formation of corrosion cells
providing timely information of any developing problems
providing data on any perceived problems to enable informed decisions to be made
providmg an alternative to shutting down for statutory periodic testing
Gauging pigging working:
During the construction phase, pigging with a pig can be one of the most significant inspection instruments available to confirm that the pipeline is laid as indicated.
In the early days of pipelining the gauging plates were made of steel. They also required some machine connected to the pig to create a sound so that the pig could be walked to where it stopped.
The noise maker may have been a drag chain, or different roller, gear or sprocket kinds and sizes. This was a means of discovering places where material left at the bottom of the ditch or material back-filled onto the pipe caused damage to the pipe.
When steel gauging flanges were used they were almost always placed on the front of the pig so that the flange would push any construction debris out of the pipeline, or the pig would stop if it encountered an obstruction.
Most contemporary gauge flanges are produced of aluminum so that indoor surfaces are not damaged by contact with the pipe. The aluminum gauge plate is generally mounted between the seals of the pigs so that the gauge plate is protected from any harm other than that caused by a diameter decrease within the pipeline.