Page 263 - Pipeline Pigging Technology

Pipeline Pigging Technology

4. the gels can support a large volume of debris, without plugging or
sticking or depositing their load in dynamic or static environments;
5. all of the gels can be chemically altered to affect the viscosity and
adhesive nature of the pig for any particular application.

Gelled fluids can be pumped through any line capable of accepting liquids
and can be used in conjunction with mechanical pigs to improve their
performance. Typical gelled fluid applications can be briefly summarized as
follows:

1. Cleaning debris from the pipeline: Where long pipelines are required
to be commissioned, and debris build-up ahead of the cleaning pigs is
considered to be a problem, gels can be used to suspend and distribute the
accumulated debris along the body of the cleaning train, allowing large
volumes of material to be suspended and removed from the line in a single run.
In the past one has often had to rely upon a large number of pig runs, usually
in combination with high-velocity flushing, requiring, in many cases, high-
horsepower pumping capability to overcome friction and ensure particle
suspension.

2. Dewatering the pipeline: Gel pigs are also used to assist in the removal
of water from the walls of a pipeline and can be manufactured to be
compatible with, and be able to contains methanol or LPA between either
high-viscosity polymer pigs or mechanical pigs. It has been found that certain
types of gels are affected by these chemicals and care has to be taken in their
selection; therefore full laboratory compatibility between the dewatering
components and the product is recommended.
Nowsco also usually proposes running a dewatering fluid and a hydrocar-
bon gel to leave the hydrocarbon pipeline oil-wet; the hydrocarbon gel can
be altered to lay down an inhibitor coat if required at the same time.

3. Acting as product-separation pigs: Gel can be used when two fluids are
to be kept apart, e.g. water and oil. Here a viscous gel pig is placed in the line
between the product. The gel system can be readily diverted on arrival and
the lack of a mechanical pig may be preferred in a production line. The type
of gel and length of gel plug are specifically designed for a particular ©Deration
depending on:

(a) type of fluid to be separated;
(b) temperatures to be found in the line;

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