Page 421 - Pipeline Pigging Technology

Pipeline Pigging Technology

There were also five tests performed with a misaligning flange installed in
the transit spool. The VetcoLog intelligent pig was tested once with a 5° offset
in the misaligning flange, and twice with a 10° offset. The TDW dual-diameter
(14x10) scraper pig and the Knapp Polly Pig dual-diameter (14x10) gauging
pig were also tested once each, with a 10° offset.

CONCLUSIONS

The test results showed that all of the pigs tested can pass through the
symmetric wye fitting geometry without problem and without damage to the
pig or the fitting. Moreover, the successful passing of each type of pig was
demonstrated under a wide range of flowing conditions, i.e. pig velocities and
flow conditions in the opposite inlet.
The tests using air with the short, light pigs, such as the foam pigs and
spheres, show that concerns over stalling pigs with high by-pass potential can
be eliminated by simply undercutting the inside of the fitting. For these types
of pigs, it is recommended that the ID of the fitting be enlarged to remove at
least one-half of the pig squeeze just prior to the crotch area. This generally
amounts to approximately a 2-4% increase in the wye fitting ID in the
undercut region.
The test results presented in this paper are exclusively for 10-in pigs and
for dual-diameter (14x10) pigs passing through a lOin x lOin x lOin piggable
wye. Additional testing is required over a range of other sizes before the
results can be generalized for all sizes.
There are a large number of pigs used routinely in pipeline construction
and production operations that have not been tested. Therefore, additional
tests are recommended to extend the conclusions to other pigs. Specifically
of interest are the other large, heavy, intelligent pigs, such as the British Gas
On Line Inspection pig and the Tubescope Linalog pig.

ACKNOWLEDGEMENTS

The authors wish to thank Transcontinental Gas Pipe Line Corporation,
HydroTech Systems, Inc, Conoco, Inc, and their joint interest owners in the
Jolliet Project, Oxy USA Inc, a subsidiary of the Occidental Petroleum Corp,
and the Four Star Oil and Gas Company, a subsidiary of Texaco Inc, for their

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