Over the last number of years several models have been developed that are now all grouped under the one heading, Piglab. These models are in various states of development, some are fully coded as usable computer programs, others are spreadsheets and still others are manual calculations.
Verification of the models is ongoing and extensive. When used in specialist pig design, the philosophy has been: –
- Use the tools to compare various pig designs, focusing in on the one most likely to work over the whole pipeline;
- When this is achieved, vary some of the more estimated parameters (eg Youngs Modulus) to make sure the pig still works over a range of inputs, homing in on the worst case. This is similar to the approach adopted by engineers designing a pipeline.
In this respect, Piglab is similar to performing tests on pigs using a loop to develop the optimal configuration. However, much more scenarios can be evaluated quickly and cost effectively.
Pipeline Research Limited’s future aim is to code all these models using Delphi and Pascal, into four tools that can be used to aid pig design processes: –
This looks at a single component, for example a disc seal, and determines factors such as distributed and net force exerted on the pipe wall, differential pressure, flip pressure and buckling. Currently sealing discs, guiders, and butterfly discs and the FTL Seals Technology Limited linked wheel suspension module can be examined.
This module examines the behaviour of a complete pig in a number of pipeline components such as straight pipe with ovality, bends with ovality and reducers. The program allows the user to check the extent of pig nose down, loss of seal, or by coupling with Piglab Module 1, the likelihood of seal flip-over. The aim of the model, in addition to dual diameter work, is to help avoid pigs getting stuck in pipelines by ensuring correct configuration and seal size.
Along with the compressible module, this is the most developed of the models and is coded as a usable computer program. This allows the user to examine the effects of distance and velocity on the behaviour of the pig in terms of differential pressure, wear and leakage. This has been successfully used to design a High Friction Pig and a Bypass Pig in past projects, and has proved a very useful tool in predicting pig behaviour.
The figure shows model output of pig differential pressure (dP) against distance. Seal wear causes the dP to drop. The pig velocity influences lubrication and therefore the seal wear.