Transcript Pipeline Current Mapper - West Virginia Corrosion Control

Radiodetection
PCM
Pipeline Current Mapper
PCM
Electromagnetic AC attenuation
and ACVG
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Radiodetection
PCM
PCM Application
• PCM will find:
– Coating defects (holidays)
– Shorts to other structures
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Radiodetection
PCM
Transmitter
• High power output
(150 Watts)
• Very low frequency to
– increase range
– reduce coupling to other
services
– reduce field distortion
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Radiodetection
PCM
Transmitter
• Powered from a
transformer/rectifier
site.
• From either rectified
DC (20 – 50 V) or
110/240 VAC.
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Radiodetection
PCM
PCM Receiver
• Identifies signal
from Transmitter
• Converts to
Current
• Log to 400 records
and download to
PC
• Connect to GPS
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Radiodetection
PCM
A-frame
• Pinpoint
holidays
• Known as ACVG
• ...but SAME
results as
DCVG.
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Radiodetection
PCM
Transmitter Connection
• Typical
Transmitter to
pipe connection
• Provides a
perfect pipe
connection point
• Anode provides
perfect ground
connection point
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Radiodetection
PCM
Transmitter Connection
• Disconnect
Rectifier
• Use same
connections to
connect the PCM
transmitter
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Radiodetection
PCM
Transmitter Connection
• Always direct connect
• Always use an independent ground
- Anode Bed
- Ground Stake
- Across an insulator?
• Always have a map of the facility
• Never use another utility as the ground
return.
• Never assume anything.
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Radiodetection
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PCM
Locating Shorts
- First signal loss may not be the short.
- There may be more than one short.
- There may be an unknown source.
Locating Coating defects
- Take readings at the same intervals.
- Make sure PCM and boot is perpendicular to the
pipe.
- Hold unit steady and upright when reading
current.
You do not always have to connect closest to the
suspected short or coating defect.
More is not always better.
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Radiodetection
PCM
Setting the Transmitter
• Three settings
available
– ELF (4+98 Hz)
– ELF + CD (8 Hz)
– LF (512 H z) +
CD
• Normal set to
ELF + CD
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Radiodetection
PCM
Setting the Transmitter
• Set Current switch
to desired current
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Radiodetection
PCM
Taking Current Readings
• If ELF and
arrows selected
on Tx then
select ELF on
the RX
• Locate pipe in
conventional
way
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Radiodetection
PCM
Taking Current Readings
• Hold the
Receiver Steady
on the ground
and press the
PCM Key.
• Current is
displayed after ~
4s
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Radiodetection
PCM
Taking Current Readings
•
Unit automatically performs steps:
1. narrow band signal processing measures
4 Hz signal (magnetometer);
2. proceed to calculate depth (twin aerials);
3. calculate current;
4. determine CD (using 4 Hz + 8 Hz shift).
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Radiodetection
PCM
Current Direction
• Indicates which direction the Current is flowing
– Aids fault analysis
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Radiodetection
PCM
Methodology using PCM for
Current Surveys
• Use an independent ground and try to mimic your CP circuit when
possible
• Make sure rectifiers are not influencing the signal (turn off AND
disconnect if necessary)
• Isolate your circuit whenever possible (disconnect bonds for better
surveys)
• Take readings at equal distances and record your distances
• Every 50 feet is a good standard (others can be used dependant on
location)
• Use it as a macro tool and depth of cover tool (use A-frame for micro)
• Look for anomalies with more than a 5% change normally
• Make sure unit is upright and perpendicular to the pipe
• Use the peak mode. Check peak and null readings and verify depth
when readings are suspect.
• Take multiple readings in one location if you suspect the accuracy.
• Know what is in the area of your pipe and what it is connected to it
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Radiodetection
PCM
Datalogging
• 400 records can be stored.
• Records can be:
– reviewed on PCM
– downloaded to a PC
• Records can be viewed on
Excel
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Radiodetection
PCM
Datalogging
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Radiodetection
PCM
A-frame
A
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Radiodetection
PCM
A-frame
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Radiodetection
PCM
PCM with A-frame for
Alternating Current Voltage Gradient Surveys
• Used as a micro and a macro survey tool
• Can be used in various soil conditions but ground contact of the probes
will affect the readings
• Rectifiers generally do not influence the ACVG survey
• In areas of high interference or where current survey does not give you
answers, ACVG can still be used with more success
• Know what is in the area of your pipe and what is connected to it
• Larger holidays can mask smaller ones until the larger holidays have been
repaired
• PCM displays A-frame readings in db or decibels. Remember every 10 db
higher is twice as large
• Metal to dirt contact and soil resistance (not necessarily size of holiday) is
what affects the db readings
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Radiodetection
PCM
ACVG Methodology
• Use an independent ground and try to mimic your CP circuit when possible
• Take readings parallel and along the pipe. When you see an arrow reversal
go perpendicular to the pipe and make sure arrow reverses over pipe
• You do not have to be right on top of the pipe when surveying
• On concrete and asphalt use wet sponges or rags on the probes or wet the
ground around the probes.
• Take readings at equal distances usually about every two to three steps
• Use the largest db reading seen around the anomaly for you records
• Record all faults seen with db readings and footages or GPS coordinates.
• Once done, anomalies can generally be categorized into 4 areas
–80db – 100db – large
–65db – 80db – medium
–50db – 65db – small
–50db and below – very small
LOCAL CONDITIONS DETERMINE WHAT IS A DIG!
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Radiodetection
PCM
Graphing in Excel and Data Interpretation
Corriente (mA)
Corpoven Tacoa
1500
1000
500
0
0
200
400
600
800
Distancia (m)
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Radiodetection
PCM
Graphing in Excel and Data Interpretation
Tramo II - K 0+510 al K 0+
800
700
Corriente PCM (mA/dB)
600
500
400
300
200
100
0
0
200
400
600
800
1000
Distancia en mts.
Datos de campo
Variación en dB
1200
1400
1600
1800
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PCM
Graphing in Excel and Data Interpretation
400
400
300
300
200
200
100
100
0
0
0
200
400
600
800
1000
Distance (m)
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Depth (m)
PCM Current
(mA)
Current Attenuation & Depth
Radiodetection
PCM
Graphing in Excel and Data Interpretation
Corriente (mA)
Gas Industrial de Monterrey
250
200
150
100
50
0
0
50
100
150
200
Distancia (m)
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Radiodetection
PCM
Graphing in Excel and Data Interpretation
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Radiodetection
PCM
Graphing in Excel and Data Interpretation
PCM Current (mA)
AC Current Drop
1500
1000
500
0
0
20
40
60
80
100
120
Distance (yd)
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Radiodetection
PCM
Graphing in Excel and Data Interpretation
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Radiodetection
PCM
Paved Street
2” Gas Main
Water Main
Typical PCM Mapping Survey
35ma
160ma
N
1” copper water service
95ma
265 ma
location of gas
main and
waterline short
561ma
590ma
358ma
3”
350ma
95ma
Paved Street
201ma
2”
325ma
Paved
Street
3”
Paved Street
Pipeline Current Mapper
transmitter with an output of 600
milliamps set-up across a gas
mainline insulator
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