VariPig for pipeline cleaning case study
The range and number of VariPig systems in use continues to grow. FTL Technology designed their next-gen multi-diameter pipeline system to accommodate a large diameter change in operation.
Among the challenges to successfully pass through the pipeline system is the initial requirement for VariPig to be launched within the small diameter pipeline, then increase into the larger diameter pipeline, before subsequently re-entering into a smaller diameter section of pipeline. The inclusion of 3D bends within the smaller diameter pipeline provided additional design challenges for the VariPig system.
Whilst the operational features of VariPig, which include multi-diameter capability, true centreline running and low differential drive pressure, are well established, this new application provided fresh challenges in seal design to ensure that the large diameter discs did not wear out during prolonged operation within the smaller diameter pipeline and that the total seal and guider package would be capable of passing through 3D bends without compromising operation.
Due to features present within the pipeline system positioning of the seal package was also vital so as to ensure sealing and drive past full bore off-takes. However, this requirement conflicts with the need to negotiate 3D bends. Detailed modelling using FTL's in-house 3D CAD software was utilised to predict how these conflicting requirements would affect operation of VariPig.
Additional Pipeline Runs for 36" VariPig
During 2003 a VariPig system was supplied to an operator to undertake a complex progressive cleaning operation in a gas pipeline. This initial operation was further complicated as the mechanical condition of the pipeline was unknown, and it was suspected that significant levels of contamination including liquid were present within the pipeline system. to record conditions within the pipeline the VariPig was equipped with a comprehensive suite of onboard electronics and sensors.
The VariPig system was selected due to its low differential drive pressure, true centreline running and ability to cope with large and varied changes in pipeline geometry. VariPig successfully completed a series of assessment and inspection runs for the operator.
Using the information gathered during 2003, a pigging strategy for 2004 was established to include additional inspection and assessment runs in both the onshore and offshore pipeline sections. To allow a more detailed assessment of pipeline conditions it was decided to install a series of enhanced sensors onto the VariPig.
FTL has completed the design changes to the VariPig system to accommodate the new sensors. Following completion of this new series of runs, VariPig will have successfully completed in excess of 1,250km with just basic routine field maintenance required to maintain operational reliability.