This paper from Pipeline Research Limited examines the issues associated with dual diameter, bi-directional pigging specifically for pipeline pre-commissioning. The technique can be used to flood and subsequently dewater a pipeline without the need for temporary subsea traps or additional support vessels.
An example is the Alve Pipeline in Norway. This 16km flow-line from the Norne Platform to the Alve Manifold includes 10” and 12” pipe section. The line was flooded from Norne using the pig with oxygen scavenge seawater and then dewatered using produced gas from the well. The pigs needed
to have a high efficiency since very low velocities were used to flood the line and in order to avoid hydrates on dewatering. Dual diameter wheel pigs were employed
with non-buckling disc type seals. This paper describes the design of the pigs and the seals to achieve the required functionality. The test facility and testing performed
to verify the pig performance is also described. Finally, an overview of the offshore pigging operation is provided.
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