Reconnaissance Pig
This pig is currently used in the Frigg Transportation System from the North Alwyn Bravo Platform to St Fergus Gas Terminal. Pigs are probably so-called because of the screeching sound made by early pigs when travelling through a pipeline.
Rather than having its own motor, the pig is propelled by the moving gas in the pipe. As well as being used to clean the pipeline, this pig can also detect dents and areas of debris build-up.
This innovative pig has a special multi diameter design and weighs approximately 0.7 tonnes. It takes 40 hours to travel the 286 mile distance, including 68 miles of 24 inch pipe before joining the Frigg 32 inch pipeline where it also has to navigate junctions and the MCP-01 bypass.
Total own two of these pigs and this one has already travelled along the pipeline. It also spends time being modified and tested in an onshore test loop. To make sure that the pipes can continue to transport gas for many years, it is likely that this pig will also be used to tow thickness inspection equipment behind it to inspect both the 24 inch and 32 inch pipe wall thickness.
Front module
The front module consists of the bumper nose, two seal packs and two suspension systems. The bumper nose has a steel bar across its nose to help it to be retrieved. The suspension systems seen on the front and rear modules are used to centre the pig in the pipeline. Within the front module is a Weatherford Smart Acquisition Analysis Module (SAAM). This is a battery powered unit that senses and records its environment so that it can locate and assess areas of debris, dents in the pipeline, record pressure and temperature.
Seal packs
Sealing discs or ‘seal packs’ are used to create a seal within the pipeline. The yellow disc is used to help guide and centre the pig in the pipeline, the red disc is used to create a seal in the 24” section of the pipeline system, while the blue disc creates a seal in the 32” section of the pipeline.
When the pig is in the 24” section of the pipeline the blue 32” seal folds into a clover type shape, eased into this form by 5 buckle inducers moulded into it. Once into the 32” section the blue disc expands and recovers to its original state to create a tight seal in the pipeline.
Rear module
The rear module on this pig is attached by a ball joint assembly and has a seal pack containing a red 24” seal and a blue 32” seal with buckle inducers. The rear module of this pig has ‘by-pass’ ports to allow gas to flow through it towards the front seal pack where it pushes the pig along the pipe. The rear module also houses large magnets that are used to gather ferrous material whilst the pig traverses the pipeline.
The rear module also houses a Nautronix EM Transmitter unit which is used to detect and track the pig when it is in the pipeline. If the pig became stuck, a receiver unit could be used by a diver or remotely operated vehicle to locate the pig. The transmitter works by emitting a pulsed, electro-magnetic field that can be detected through the pipe wall, and to an extent through soils. The unit extrudes from the rear of the pig so the field is not restricted by any magnetic material.
