Page 389 - Pipeline Pigging Technology

Pipeline Pigging Technology

they pass through the junction. The wye piece has external stiffeners, and the
web between the incoming bores is cut back and rounded off. This design has
been successfully manufactured by two routes: both by casting and machin-
ing the bores, and also by forging components, welding them together and
then machining.
The Ula pipeline has been pigged regularly, at intervals of about every two
weeks, for wax removal. Cupped pigs with elongated bodies are used such
that there is always at least one set of cups sealing to provide the drive as the
pig negotiates the enlarged bore at the wye.
Statoil has now connected the Gyda pipeline to the spare branch of the
Ula wye, and has installed a second wye of the same design in the Gyda line
still leaving a connection available for further entrants. This combination of
two wyes in series has been successfully pigged on a regular basis for wax
removal since Gyda started exporting oil in June, 1990.
Statoil has installed a third wye junction, connecting the 16-in Vestefrikk
and Oseberg C pipelines to OsebergA. This reinforces the marked trend for
those, such as Occidental and Statoil, who already have wye junctions, to
install more. Two further operators are to install wyes, both of them large-
diameter. One is to be inserted in the 32-in Frigg to MCP-01 gas pipeline for
the Total Bruce project, and the other in the 30-in Beryl pipeline by Mobil. As
shown in Table 1, these latter are significantly larger than the 16 to 20-in wyes
presently in service.

RESEARCH AND DEVELOPMENT

A comprehensive testing programme was carried out to develop the Statoil
wye design and prove its piggability. The tests were carried out by
A.R.Reinertsen AS for the Statoil Ula project in 1983-85. They were based
initially on a 6-in acrylic plastic water-driven loop, where a variety of types of
pig were observed passing through a convergent wye [ 1 ]. In the course of 450
runs, a preferred concept for the wye was selected and the branch angle
optimized. A further 100 runs were then carried out on a full-scale 20-in water-
driven loop with a translucent glass fibre wye, demonstrating that conven-
tional pigs, spheres, welding bladders, and inspection vehicles would all pass
though successfully. This bore design was used for Statoil's wyes, and has
demonstrated itself to be reliably piggable in operation.
Testing programmes of wyes have also been carried out by BHRA at
Cranfield and British Gas, believed to be 4 and 8-in scale model tests and full-
scale pull-through tests of on-line inspection vehicles respectively.

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