1. University of Bristol, Cleaning and separation in fluid flow conduits, UK Patent Application No GB 2358229 A, Published 18.07.2001
2. A good Web source for general pigging and its background: www.pigsource.com
3. J.L. Cordell, Pigging research, Pipeline Pigging and Inspection Technology Conference, Houston, February 1991
4. A. Vingerhagen, J.L. Cordell, The design and development of multi-diameter pigs for pipelines and flexible risers, Pipeline Pigging and Inspection Technology Conference, Houston, February 1997