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Chasing pigs

Company:

Tay Communications is an electronic engineering firm headquartered in Dundee, Scotland. The company was contracted by a global energy and petrochemical company to provide telemetry services for the cleaning of a gas pipeline located near Norwich in the UK.

Issue:

Gas pipelines require daily cleaning and maintenance through a process called ‘pigging’. Critically this cleaning process needs to be achieved without stopping the flow of the gas in the pipeline. This is achieved by inserting the Pipeline Inspection Gauges, or pig, into a Y-shaped kicker line section in the pipeline known as the 'pig launcher'. When this launching station is closed the pressure-driven flow of gas in the pipeline is harnessed to push the pig down the pipe until it reaches a receiving station known as the 'pig catcher.' Each pig is equipped with plastic disks which rub against the inside of the pipe as they pass through, removing sedimentation and build up of scale. The pigs also carry magnets which then attract any loose metal objects in the pipe for removal.

In the case of the Norwich pipeline, up to five pigs would be run daily through the pipeline. The system is designed to send the pig through the pipeline in either direction, but must be able to track the dispatch and arrival of each pig, as a blockage in the pipeline may require the pigs to be pushed back to the launcher.

The pipeline operator needed to automatically track these pigs, requiring telemetry operating at ranges of up to a quarter of a mile to the pipeline control centre. To achieve this through a hardwired system would be extremely complex, so the company approached Tay Communications to supply a simple and cost effective wireless based system.

As the system is used to transport gas, Tay Communications needed to ensure any wireless components used would be intrinsically safe to avoid catastrophic damage to the pipeline.

Solution:

Tay Communications, sought a license exempt radio link which could be used for a SCADA (Supervisory Control And Data Acquisition) system and which would be intrinsically safe. It chose wireless specialist Wood & Douglas and its Sentinel range of telemetry radios.

Tay Communications selected the ER450 Digital Outstation, which is designed specifically for data transmission applications within Point-to-Point SCADA systems. Crucially, the ER450 is intrinsically safe, and when built into a special housing by Tay Communications became ATEX approved for use in potentially explosive atmospheres.

Deploying a UHF SCADA radio system enables Tay Communications to use a ‘polling’ method for monitoring the movement of the pigs. The Master radio in the control centre transmits requests to the ER450 outstation locations and receives responses containing the current Remote Terminal Unit (RTU) values. The RTU is a monitoring device which interfaces with the physical world, in this case by detecting the passage of the magnet on the pig as it passes in and out of the gas pipeline.

If the RTU detects a pig entering the pipeline, but not exiting, an alert will immediately sound in the control centre and a crew can be dispatched to investigate or clear the blockage, providing early warning of potential problems and minimising any cessation of transport of gas through the pipeline.

  • Intrinsically safe license exempt radio link for potentially explosive environment
  • Replaces expensive fixed line alternative

Visit: www.tay-comms.co.uk

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