.
Compliments of
5a+-
Flowmore Services
19515 FM 149 Box 150 Houston, TX 77070
-
Product Application
Pigging outhow one millrestored
capacity to its treatedeffluent pipeline*
f)
3
1-800-FLOWMOR
The capacity of a 13-mile-long effluent
pipeline at Champion International’s
mill in Sheldon, Tex. had dropped from
25 million gallday to 17 million gal/day
during the course of its 20-year lifespan.
With an effluent flow of 16-18 million
gallday, the shrinking capacity of the 42in.-diam. reinforced concrete pipeline
was a matter of concern. During periods
of high flow, treated effluent was backing up into the final clarifiers, hydraulically overloading t h e liquid-solids
separation process. Heavy rains in June
1985caused floodingall the way up to the
aeration basins and tripped the fixed
aerators. With the aerators dut of service, there was no no way to transfer oxygen to the effluent. Consequently, the
BOD (biochemical oxygen demand) of
the mill effluent exceeded maximum limits for three consecutive days. The mill
informed the EPA and the state water
commission of what had happened. After
meeting with these agencies, the mill
decided t o install an oxygen-injection
system along with floating mixers. This
was a short-term solution that would
allow the mill t o stay within the BOD
limits during flooding conditions. The
long-range plan was to inspect the pipeline and find out what was restricting the
flow. The pipeline, which runs underground at depths of 5-20 ft, has 11 manholes spaced unevenly along its 18mile
length. T h e mill installed p r e s s u r e
gauges at t h e various manholes and
developed a correlation between the flow
being pumped and the drop in pressure
across t h e pipeline. The results indicated a problem in the central portion of
the line. A shutdown of the entire mill
provided Tanwir Badar, Champion’s
environmental services manager, a fourday window to arrange for a three-man
team to enter the line to inspect it and
collect samples. The inspector crawled
into the pipe with a self-contained air
*B;wetl on a paper presented at the 1988 Environmenhl Conference by ‘Idnwir A. Radar, manager of
environmental xervicesat Champion International.
supply. The two members ofthe support
team stayed at the manhole, where they
monitored the pulse rate and blood pressure of the man in the line. Radio contact
was maintained at all times. In one particularly inaccessible portion of the pipeline, the inspector was underground for
14 hours. Food, water, and a i r were
passed through two holes bored into the
pipe. Inspection revealed a buildup of
soft sludge on the walls ranging in thickness from 0.25 in. a t the beginning of the
line to 5 in. at the discharge point. The
sludge buildup reduced the effective
diameter of the pipeline t o 36 in. This
was sufficient to explain the reduction in
flow-through capacity. Having established the cause of the reduced flow, the
mill had to find a method of cleaning the
pipeline without shutting the mill down.
In addition, the state water commission
made it clear that the sludge could not be
discharged from the pipeline all a t once.
The mill chose t o remove t h e sludge
buildup by forcing a bullet-shaped projectile through the pipeline. The projectile, commonly referred to as a “pig,”
s c r a p e s t h e s l u d g e off a s i t moves
through the line. Flowmore Service
Corp., a Houston-based company specializing in pipeline cleaning, was hired
to complete the pyoject. They opted t o
use a “progressive pigging” strategy
that involved running successively fatter
pigs through the pipeline, with a one-day
interval between each of six runs. This
approach fulfilled the state’s dictum for a
gradual discharge of the sludge buildup.
I t also minimized the chance of hanging a
pig up in the pipeline. Management was
concerned that a stuck pig might force a
mill shutdown. nansmitters embedded
in the pigs allowed the mill to track their
progress through the pipeiine. The pigs
used to clean water pipelines are made of
polyurethane. The length of a poly pig is
about twice its diameter. This prevents
the pig from turning or tumbling while it
is inside the pipe. Frictional drag is created by using a pig with a diameter that
is 2%larger than the inside diameter of
the pipe. This drag is enhanced by the
pressure of the propelling media, which
compresses the pig longitudinally and
expands it radially. Poly pigs vary in density and design, depending on the job for
which they are intended. Flowmore used
three types of pigs in Champion’s pipeline. A low-density (2 lb/ft’) pig was used
for the first pass. This pig-designed for
light wiping and cleaning-is made of
foam that will shred easily in the event of
a pipe hangup. A heavier-density (5 lb/
ft:) pig with a urethane rubber coating
was used f w the second pass. This pig is
designed to remove soft buildup. In later
runs, a 5-lb/ft1pig with a criss-cross patt e r n of wire brushes was used. This
design provides maximum scraping and,
brushing action. The first two runs were
made with 36-in.-diam. pigs. The diameter was increased to 40-in. for the next
two runs and to 42-in. for the final two
runs. Since completion of the progressive pigging operation in June 1986, the
mill has been pumping effluent at rates
of 2 Z 2 3 million gallday. The waste treatment plant has not experienced any
flooding since restoration of the pipeline’s design capacity, nor have there
been any BOD excursions caused by an
inability t o t r a n s f e r oxygen t o t h e
treated mill effluent. The mill ran two
more poly pigs in November 1987to keep
the line clean. This procedure will be
repeated annually as part of the mill’s
preventive maintenance program.
LDoug Burke
Freelance editor
specializing in the pulp
and paper industry
Reprinted from Focus on Predictive Maintenance, A Tappi Journal Publication, August 1988.
Copyright 1988 by TAPPI, and reprinted by permission of the copyright owner.