Page 187 - Pipeline Pigging Technology

Pipeline Pigging Technology

were used for Phase 1 and Phase 2, respectively. This is enough gel to
potentially entrain 36,400 and 18,2001bs of debris, respectively.
Originally, the service proposed for each phase included two trains, one
for crude oil removal and one for the removal of debris. These two trains were
incorporated into a single pig train; this eliminated certain components
which performed the same task, reducing service time, and ultimately
increasing the efficiency and feasibility of the service. The gellypig train
design utilized comprised several parts (see Fig.2.).

GELLYPIG TRAIN COMPONENTS

The major components of the train and a general description of their
functions are listed as follows:
1. Separator gels - these are a very thick, viscoelastic polymer with strong
cohesive properties. The separator gels help to keep the pig train intact,
acting as one large cohesive plug in the front and rear of the train. The
separator gel in the front helps to prevent runaway pig trains and keep the
debris gels in full contact with the pipe walls, without the rigidity of a
mechanical pig, which could become stuck. In the rear, the separator gels
help maintain a better seal and displace other fluids in the pipeline more
efficiently.
2. Debris gels - these are a very sticky polymer with strong adhesive
properties. The debris gels entrain loose debris into the gel slug, with a
"tractor motion", as it moves down the pipeline. The debris is then suspended
in the gel. Typically, a "design" value of Igall of debris gel is used for each
pound of debris in the pipeline. A mechanical (or foam) pig is mandatory
behind the debris gel, for the proper dynamics to occur within the gel slug.
Excessive debris "ploughed" up by the mechanical pig is carried away from
the pig and entrained throughout the debris gel slug.
3. M289/F05 7 degreaser- this is a water-based caustic degreaser, compris-
ing a mixture of four DS chemicals, including a surfactant. A volume of
approximately 20,000gal of degreaser was used for each of the two phases.
This was a considerably lower volume than the calculated amount from the
laboratory analysis (see Table 2).
The lower volume was used to reduce costs and simplify logistics. This
volume (20,000gal), would be appropriate to maintain 1 hour of contact time
at Ift/sec. The gellypig train would utilize the degreaser to "loosen" hydrocar-
bons dynamically, as opposed to completely dissolving them statically. The

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