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Introduction
Pipeline
Pigs
are dispatched through
pipelines to perform
various functions:
1: To
clean the
inner wall of the pipeline.
2.
To swab
the line free of liquids.
3.
To fill
the line during testing
stages.
4.
To
internally gauge the line
geometrically.
5.
To
inspect the line for internal
corrosion.
6.
For
product separation - in
multi-product lines.
7.
Miscellaneous
operations utilizing
connection
with on line maintenance programs.
Pigs
may take
the form of two, three, or
four urethane
cups which are mounted on a mandrel.
Multi-section mandrels - for
inspection
purposes, poly pigs, cast urethane pigs, or
spherical pigs.
Anytime
that a
pig is introduced into a
pipeline, there
are uncertainties as to its whereabouts. Many
of the problems
associated
with pipeline operations, or maintenance may
be attributed to pigging
operations.
When a
pig
becomes lost, or jammed, the
major problem
is the location of the pig with a high degree
of accuracy.
During
the
last decade, there have been
many companies
who have produced devices which are intended
to assist in tracking pigs
in both land and marine operations. These
devices take various forms:
a.
Acoustical
b.
Radio
transmitters
c.
Radioactive
material
d.
Noise
makers
e.
Magnetic
Each
of these
devices will work given
the correct circumstances.
The
Acoustic
Device
is usually
called a "pinger" as this
emits interrupted
acoustic signals. It has many benefits
in offshore pipelines for
defining
the pig's passage through a general
area. Its success has been limited
for the following reasons:
- Unit
is battery operated, and
therefore has a limited
operational
life.
Poor
position accuracy.
Acoustics echo in all directions,
and is therefore very difficult to
pinpoint.
- Requires
a liquid interface and
therefore cannot be utilized
in a dry line i.e. gas pipeline.
- Cannot
be utilized in land
lines.
- Large
physical size.
- Hazardous
environment,
vibration / shock
- Must
use correct frequencies.
The
amount of overburden over the
pipeline will prevent
the passage of audio signals.
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The
Radio Transmitter
is a
battery operated unit which is
attached to the pig.
In order to
penetrate the pipe wall,
which is a natural
screen against radio signals, the
chosen frequency has to be extremely
low. The resultant signal through the
pipe wall is minute, and in
consequence
the receiving unit has to be ultra
sensitive.
The main
difficulties with this
device are:
- Unit
is battery operated
therefore has a limited
operational
life.
- Very
limited range.
- Impossible
to operate in high
electrical interference areas.
- Requires
continuous monitoring
/ leap froging.
- No
remote signaling facilities.
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Radioactive
Materials
are
encapsulated in a small container
housed within the
body of the pig.
This
method is not recommended for
the following reasons:
- Possible
health hazard.
- Possible
contamination of the
pipeline.
- Requires
a high level of
material to be effective, handling
difficulties.
- Does
not allow for remote
monitoring, or systemization.
- Not
acceptable in most
countries in the world.
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Noise
Makers
are
probably the earliest form of pig
tracking. This
requires either a cam type device or a
metal chain which makes a noise
as the pig travels through the
pipeline.
This
method cannot be recommended
for the following reasons:
- The
device is primitive, and
not conductive with modern
engineering
practices.
- In
order to detect its passage,
it requires labor to lay
with an ear to the ground or vent
post to listen for the pig
- In
the event that the pig does
become stuck, it cannot be
located.
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The
StarTrak
Pigging Magnetic Pig Systemconsists
of
four
elements:
1.
Pipeline Magnetic Pig
2. Station
Magnetometer or Static.
3. Flux
gate Gradiometer - Search
Instrument.
4.
Port-a-Sig
Magnetic
Pig:
The pig is designed as a magnetic
circuit with a field strength
sufficient
to saturate the wall of the pipe
through which it is traveling. The
pig
normally comprises of a steel body
which houses the magnetic section,
four
urethane cups, urethane spacers, a
nose plate designed to take shock,
and
a rear locking plate. The Magnetic
circuit may take the form of the
entire
pig body, as in small size pigs or a
collar in larger diameter pigs.
The
collar is made up of two mild steel
discs with independent magnetic
modules
around the center-line of the
circle. The magnetic circuit may be
used
in conjunction with cast urethane
pigs, poly pigs, or spherical pigs.
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Station
Magnetometers:
The station or static magnetometers are remote
field passage indicators
which allow the operator to track the pig
through sections of line.
These
units not only indicate the pig's arrival at
that point, but indicate
also
the time of the event. An output from the unit
can also give a relay
closure,
thus providing for any number of ancillary
devices, i.e. radio
telemetry,
sona-alert (audio alarm), or input into the
clients' SCADA network.
Normally,
indication is facilitated by high intensity
strobing beacon which can
be
seen from long distances especially from the
air, and at night. The
station
indicators may take the form of either
portable or permanent
installations,
or in marine applications, be sub sea or buoy
mounted. Add to this
Satellite
communications and this unit will give our
clients all the flexibility
they need.
Flux
Gate
Gradiometer: This
instrument provides a very essential part of
the total system, it is
used
to locate the whereabouts of a pig should it
become lost in a line. The
gradiometer may take the form of a portable
hand held unit, a "fish"
for
offshore location of pipelines or magnetic
pigs, or be used in
conjunction
with an R.O.V. or with an airborne vehicle .
The Flux Gate Gradiometer
is designed to sense magnetic fields which
exist around all magnetic
objects.
These steady magnetic fields penetrate soil
and water, and so indicate
the presence of magnetic objects which may be
buried, or hidden from
view.
Two
flux gate
sensors are contained within
a sensor tube
with a spacing of typically of one half meter
and are aligned
mechanically
to within two seconds. The sensor tube can
either be detached, or
mounted
directly to an electronics housing which also
consists of a display.
The
difference in the magnetic field between the
two sensors is presented
on
the display which may take the form of either
a meter movement, or a
digital
display, and also can be used to drive a
remote display or recorder.
The
device lends itself to interfacing with
various computers.
Port-a-Sig:
Launch
and receive alert. This instrument complements
the system as it was
designed
to be used with or without the other station
devices and is sold as a
pig
alert device which will respond to the arrival
or departure of a pig
containing
a small magnetic collar or spacer. The unit,
as its name suggests is
completely
portable, and can be used on any line size. It
has the unique feature
of
being intrusive free, and not prone to
corrosion either internally or
externally
as are other signaling devices. This
instrument not only signals the
arrival
or departure of a pig, but can count the
number of pigs and times.
A
manual mode
will ensure that the unit
continues to
be activated, recording the times of the
event, until it is physically
turned off. In the auto re-set mode the unit
will re-set itself
normally
20 seconds to await the arrival of further
pigs. Port-A-Sig signals, by
high intensity strobing beacon and also
provide a relay closure for
integration
into automatic systems i.e., opening /closing
valves.
The
unit is
powered by 12 volts and can be
used with
lithium batteries or solar power.
Operations:
On
Land:
Prior
to the
operation, alignment sheets
should be studied
in order to choose the best practical location
of the static
magnetometers.
Where possible, areas of accessibility are the
obvious location to site
the stations. However, vulnerable places such
as road crossings, bends,
rivers, and railroad tracks should be
addressed. The static
magnetometers
are normally spaced at intervals of typically
one mile or convenient
locations.
From alignment sheets one can obtain the exact
linear location of
stations.
Dependent on whether the propellant is a
liquid, gas, or air, it should
be possible to work out an estimated time for
the pig's arrival at each
location.

The
installation
of the static
magnetometers is a very
simple operation. The line is located using a
pipe locator or
gradiometer,
and a depth measurement noted. A small 2" hole
is augured just off the
line of pipe, as it is not necessity to make
direct contact with the
pipe.
The sensor tube is installed normally 2-4 ft.
above the line, and made
firm, then the static head is attached and the
unit turned to the on
position.
It
must be
noted that in areas where the
line is buried
deeply it is not practical to use the static
magnetometers, and these
areas
should be monitored by the Gradiometer.
When
all static
magnetometers have been
positioned, the
pig may be launched. It will first pass the
Port-a-Sig which is sited
at
the pipe directly before it enters the ground.
This ensures a
satisfactory
launch. The Port-a-Sig will immediately
respond by signaling the
passage
of the pig.
The
operator
will then keep constant
recordings of line
pressure at both ends of the line. As the pig
passes each static,
indication
will be given allowing the ETA of the pig's
arrival at the next station
to be up-dated.
In the
event that
the pig becomes stuck,
the first indication
will be an increase in pressure at the launch
trap and a decrease in
pressure
at the receiving trap. By timing the operation
accurately, and
correlating
this against known speed of the pig, it is
possible to calculate the
location
of the obstruction to within 100 ft.
At
this point,
an operator using a flux
gate gradiometer
will go to the area, locate the line, and
conduct the search for the
pig.
The Gradiometer will respond both on the
visual display and by its
in built
audio system. By excavation, the defect
usually becomes apparent and
can
be corrected.
Offshore:
Marine
operations
more skill on the part of
the operator
both during setup procedures, and positive
location of the defective
area.
The operation is basically the same for
offshore as it is on land.
The
line
should be buoyed at strategic
locations, and
the marine magnetometer sensors installed with
weights.
In
order to
obtain valuable information
on how the pig
is running, it is advisable to set up two
points near to the launch.
This
will provide a key as to how the pig is
traveling which may be used to
assist in the event the pig gets jammed.
In
the event
the pig does stick, a diver
equipped with
a marine gradiometer can be used to determine
the exact location of the
pig. In deeper water, an R.O.V. mounted with
gradiometer can be used to
locate the pig.
StarTrak
Pigging
Technology Inc.,
Pipeline Systems & Servicein
Katy Texas. U.S.A.
We
specialize in
a unique brand of services
to the World-Wide
Pipeline Industry. The uniqueness of StarTrak
stems from its in-house
development
of equipment, the specialist training of
employees, the quality control
of work and the sheer desire to provide
clients with a higher standard
of workmanship than any of the competition.
StarTrak
has
provided services and
engineering consulting
throughout many parts of the world for both
land and marine pipeline
facilities.
As a
result of
the extensive field
services combined with
research and development, which has been
carried out by StarTrak's
engineering
staff, the company is able to present a line
of products which will
bring
a new technical dimension to the industry.
Services
:
- Location
-
Profiling - Computerized
mapping of all buried
pipeline and utility networks on land and
offshore
- River
Crossing
Surveys - Full Profile
- Electronic Utilizing
StarTrak "One-Pass" system
- Detectable
Pigging
Operations - Land
and Marine. StarTrak
"Pathfinder" magnetic pigging system
- Detection
of
pipeline intrusions and
leaks.
- Pipeline
Wrapping
Evaluation -
Computerized System Location
of areas with poor wrapping
- Pipeline
Engineering
Efficiency
Studies
Products
:
·
Urethane
Scraper Cups
·
Pipeline
Pigs - Cleaning - Gauging
- Detection
Equipment
·
Electromagnetic
Location
Instruments - Magnetic
Sensing Equipment - Flux gate
Gradiometer
·
Permanent
Pig Monitoring Systems
·
Port-a-Sig
Non intrusive Pig
Monitoring Units
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