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1
Pipeline Current MapperPCM
Radiodetection PCM
Electromagnetic AC attenuation and ACVG
2
PCM Application
• PCM will find:
– Coating defects (holidays)
– Shorts to other structures
Radiodetection PCM
3
Transmitter
• High power output
(150 Watts)
• Very low frequency to – increase range– reduce coupling to other
services– reduce field distortion
Radiodetection PCM
4
Transmitter
• Powered from a transformer/rectifier site.
• From either rectified DC (20 – 50 V) or 110/240 VAC.
Radiodetection PCM
5
PCM Receiver• Identifies signal
from Transmitter• Converts to Current• Log to 400 records
and download to PC
• Connect to GPS
Radiodetection PCM
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A-frame
• Pinpoint holidays
• Known as ACVG
• ...but SAME results as DCVG.
Radiodetection PCM
7
Transmitter Connection• Typical Transmitter
to pipe connection• Provides a perfect
pipe connection point
• Anode provides perfect ground connection point
Radiodetection PCM
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Transmitter Connection
• Disconnect Rectifier
• Use same connections to connect the PCM transmitter
Radiodetection PCM
9
Transmitter Connection
Radiodetection PCM
• 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.
10
Radiodetection 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.
11
Setting the Transmitter• Three settings
available– ELF (4+98 Hz)– ELF + CD (8 Hz)– LF (512 H z) +
CD
• Normal set to ELF + CD
Radiodetection PCM
12
Setting the Transmitter
• Set Current switch to desired current
Radiodetection PCM
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Taking Current Readings
• If ELF and arrows selected on Tx then select ELF on the RX
• Locate pipe in conventional way
Radiodetection PCM
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Taking Current Readings• Hold the
Receiver Steady on the ground and press the PCM Key.
• Current is displayed after ~ 4 s
Radiodetection PCM
15
Taking Current Readings
Radiodetection PCM
• 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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Current Direction• Indicates which direction the Current is flowing
– Aids fault analysis
Radiodetection PCM
Transmitter
short
target line
17
18
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
19
Datalogging
• 400 records can be stored.
• Records can be:– reviewed on PCM – downloaded to a PC
• Records can be viewed on Excel
Radiodetection PCM
20
Datalogging
Radiodetection PCM
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TransmitterA-Frame
A-frame
Radiodetection PCM
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A-frame
Radiodetection PCM
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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
25
ACVG Methodology
Radiodetection PCM
• 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!
26
Radiodetection PCM
Graphing in Excel and Data Interpretation
Corpoven Tacoa
0
500
1000
1500
0 200 400 600 800
Distancia (m)
Co
rrie
nte
(m
A)
27
Radiodetection PCM
Tramo II - K 0+510 al K 0+
0
100
200
300
400
500
600
700
800
0 200 400 600 800 1000 1200 1400 1600 1800
Distancia en mts.
Co
rrie
nte
PC
M (m
A/d
B)
Datos de campo Variación en dB
Graphing in Excel and Data Interpretation
28
Radiodetection PCM
Graphing in Excel and Data Interpretation
Current Attenuation & Depth
0
100
200
300
400
0 200 400 600 800 1000
Distance (m)
PC
M C
urr
ent
(mA
)
0
100
200
300
400
De
pth
(m
)
29
Radiodetection PCM
Gas Industrial de Monterrey
0
50
100
150
200
250
0 50 100 150 200
Distancia (m)
Co
rrie
nte
(m
A)
Graphing in Excel and Data Interpretation
30
Radiodetection PCM
Graphing in Excel and Data Interpretation
31
Radiodetection PCM
AC Current Drop
0
500
1000
1500
0 20 40 60 80 100 120
Distance (yd)
PC
M C
urr
ent
(mA
)
Graphing in Excel and Data Interpretation
32
Radiodetection PCM
Graphing in Excel and Data Interpretation
333”
1” copper water service
2” Gas Main
3”
2”
350ma
35m
a32
5ma
201m
a
95ma 265 ma
358ma
561m
a
Pipeline Current Mappertransmitter with an output of 600milliamps set-up across a gasmainline insulator
16
0m
a95
ma
Wa
ter
Ma
in
N
location of gasmain andwaterline short
Pa
ve
d S
tre
et
Pa
ve
dS
tre
et
Paved Street
Paved Street
Typical PCM Mapping Survey
Radiodetection PCM