Page 461 - Pipeline Pigging Technology

Pipeline Pigging Technology

SURFACE PREPARATION

The objective of surface preparation is to remove all deposits, including
rust, scale, and salts that could interfere with the coating bond, from the line.
It is highly desirable to create a deep, angular anchor pattern to which the
coating will best adhere. After cleaning, the line should also be completely dry
and blanketed by an inert gas to prevent flash rusting. All of these conditions
can be achieved by SANDJET, the abrasive blasting procedure used in the
InnerCure Pipeline Renewal Service developed by UCISCO (Union Carbide
Industrial Services Co).
The SANDJET process involves scouring the inside of the pipeline with an
abrasive material, such as flint, which is propelled in a high-velocity stream of
nitrogen. The cleaning particles impinge upon the wall of the pipe at a low
angle of incidence, gouging and/or chipping away at the deposit. All waste
material is carried through the line with the nitrogen, and can be collected at
the outlet. Because the pressure drops and the velocity increases as the
nitrogen flows through the line, cleaning is more efficient in the outlet half of
the line. Therefore, cleaning is typically performed in both directions to
provide optimum surface preparation. After abrasive cleaning, pigs and/or
solvents are used to remove any remaining dust. Erosion is minimized by
tightly controlling the velocities of the nitrogen and cleaning material. The
process can clean around any bends or elbows.
The equipment needed for the cleaning process consists of:

1. a mobile nitrogen pumping unit, usually a pumper truck (which
vaporizes liquid nitrogen) or a tube trailer (which contains high-
pressure gaseous nitrogen);
2. a trailer-mounted cleaning unit consisting of a feed pot and all
equipment to accurately control the nitrogen flowrate and velocity
and the feedrate of the cleaning material;
3. an injection device which is connected to the pipe's inlet by a
standard flange;
4. a dust-suppression/waste-collection system, usually a vacuum truck
or covered dumpster. All waste material is dry and easily disposed of
by the customer.

Occasionally, SANDJET cleaning may uncover very thin, hard deposits,
such as magnetite, which are more economically cleaned with chemicals. If
this is the case, the line is abrasively cleaned again after chemically cleaning
to re-establish the desired anchor pattern and remove chemical residue. Also,

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