EXTERNALCORROSION DIRECT ASSESMENT (ECDA)
SURVEYS & MONITORING TECHNIQUES
AN OVERVIEW
CLEARLY THE BEST
PROTECTION FOR YOUR
INVESTMENT
External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Close Interval Potential Survey (CIPS)
These surveys are carried out to validate the
overall effectiveness of the Cathodic Protection
system and involve taking potential readings along
the whole pipeline route at equidistant spacing. On
Impressed Current systems, On and Off potentials
are usually recorded, taking both readings every
metre. Current interrupters are set up in
synchronization with the datalogger commonly at a
switching ratio of 4 : 1 On : Off to prevent pipeline
depolarisation. A timing cycle of 0.8 seconds On
and 0.2 Off is also commonly adopted.
Specialist Dataloggers and Current Interrupters
are utilised for the survey and all collected data
is downloaded to allow interpretation and
presentation. This can be done in specialist
database type programs or using typical
spreadsheet applications (Excel, Lotus etc.)
To ensure correct interpretation of CIPS data,
particularly in areas of stray current interaction,
a simultaneous "static" pipe to soil potential is
always recorded. This is done utilising a second
Datalogger at a representative test location
during the survey
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Direct Current Voltage Gradient (DCVG)
DCVG is a method developed to determine and
evaluate the condition of pipeline coatings. As
the coating is the prime corrosion defence
mechanism it is important to be able to assess
its effectiveness particularly in situations where
the status of the secondary corrosion
prevention system (the Cathodic Protection
system) is in question.
A common method uses a highly accurate and multi
ranged centre zero voltmeter in conjunction with half
cells and current interrupters. Voltage gradients in
the soil are measured along the pipeline route and
localised changes in gradients measured. This
indicates increased current flow and by deduction
usually means a coating defect is present. The
accuracy of the instrument and the skill of the
operator allows detailed investigation of the location
and the collected data can be interpreted to
categorise all defects along the route and prioritise
on coating repairs. When used in conjunction with
CIPS surveys, accurate comparisons can be made to
determine areas of the pipeline with a combination of
defects and a lack of cathodic protection and is an
accepted ECDA methodology.
TYPICAL DCVG GRAPH
300
OL/RE in Millivolts to Cu/CUSO4
250
200
150
100
50
0
1
2
3
4
5
Defect Number
2
6
7
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Routine Monitoring
We work with operators worldwide to help
them manage CP systems and pipeline
infrastructure.
CP
inspections
include
functional, interim and major inspections and
are completed by monitoring Transformer
Rectifiers, Test Points, Bonds etc. This provides
the necessary information, however, without
proper management this information is
ineffective.
We have worked for many years with the AI Ltd
range of PCS Software modules to manage
large data quantities including test station,
rectifier, galvanic anode, foreign bond, isolated
services and tank CP performance, compliance,
and repair data as well as hundreds of other
related data fields across the pipeline.
Testing and monitoring of cathodic protection systems
The most significant test used in the monitoring of CP
systems is the structure-to-electrolyte potential. Generally
this is taken by connecting the structure to a calibrated
reference electrode through a voltmeter and measuring the
potential difference.
Typical reference electrodes for use in soil and water are
copper/copper sulphate, silver/silver chloride or zinc. The
reference electrodes can be permanently installed with or
without coupons (a bare area of metal) or portable. The
measurement of potentials will ideally be “IR free” which
removes the effect of applying a voltage (the CP system)
onto the structure.
Other common CP measurements are:
• integrity of isolation flanges and joints using an “IF
tester”
• current monitoring with clamp or swain meters
• measuring the voltage and current flow from the power
source with multimeters
• measuring soil resistivity prior to the design of a
cathodic protection system. This is critical in the sizing of
anodes and ground beds. It can be achieved with
speciality earth testers for surface measurements and
application of the Wenner or Schlumberger 4 pin
methods of analysis. Other techniques, such as Geonics,
can achieve greater depths in higher resistance
environments.
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Protection
Protection Criteria
Criteria
Typical protection criteria for structure-to-electrolyte
potentials (in contact with soil / water) are as
recommended within industry standards and are in
summary:
•
•
•
•
-850 mV vs. Cu|CuSO4 reference electrode for steel in
aerated soils / water.
-950 mV vs. Cu|CuSO4 reference electrode for steel in
anaerobic soils confirmed presence of active sulphate
reducing bacteria.
All above potentials are IR free or “off” potentials.
Alternative criterion – a minimum of 100 mV of cathodic
polarisation between the structure and a stable
electrode contacting the electrolyte. The formation or
decay of polarisation can be measured to satisfy this
criterion.
Equipment
Choosing the right equipment with which to perform your monitoring and survey work is crucial. CPCL
work with the leading companies in the field to ensure that all equipment is fit for the site conditions
and will enable the operator to perform the survey accurately and in good time
Field Computers
The Allegro MX is the newest generation of field data
PC and features a faster than ever processor
operating on the latest Windows Mobile® 6.1 Classic
operating system (including Microsoft Office®,
Outlook® and Explorer® suite). Colour and B&W
display options are available. It works with standard
and GPS synchronized current interrupters and is
100% compatible with Version 6 and 7 of AI’s
Pipeline Compliance System Software (PCS).
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Data
Data Loggers
The CP Logger is a small, rugged device ideal for
taking cathodic protection measurements using a
high impedance, filtered input. Potential applications
include:
•
•
•
•
•
•
Pipe-to-soil readings for depolarization
studies.
Stray current interference studies.
Verify polarization during interruption surveys.
Log rectifier output current, voltage or bond
current.
Any logging application that requires multimeter type DC input characteristics.
The CP Logger is easy to use and setup. It
has adjustable input ranges (1-100mV, 110V, and 0-100V) with excellent resolution
and accuracy. Battery life is sufficient for up
to ten days.
Current Interrupters
American Innovations offers two flexible, fully
programmable, GPS synchronized current
interrupters as part of i-series Survey
Solutions—the MicroMax® GPS200 and
MicroMax® GPS80. These interrupters offer
a number of benefits and functionality, such
as:
• Relay independent.
• GPS timing synchronization.
• Auto-resume of selected interruption
schedule upon return of power after
power loss, so it is not necessary to
travel to the field to reset the
interrupter.
• Interrupt multiple rectifiers with one
MicroMax.
• User-defined interruption schedules:
up to 4 in the MicroMax GPS80 and
up to 9 in the MicroMax GPS200.
• MicroMax GPS80 in conjunction with
a Bullhorn ICP+ remote monitoring
unit can provide a remote GPS
synchronized current interruption
option.
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Accessories
CPCL offer a full range of accessories for corrosion
and cathodic monitoring activities including
•
Reference Electrodes
•
Survey Back Packs & Poles
•
Survey Wire
•
Clips, Leads & Spares
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
Projects
Sonahess
A major Oil operator in Algeria is completing an
upgrade project to its existing facilities. Oil
production in the fields started in the 1960’s and
much of the infrastructure has been in place since
that time with additions and upgrades made in the
1970’s and latterly in the 1990’s. The prime
present objective is to upgrade and add to these
facilities to increase production from c. 30,000
BOPD to c. 80,000 BOPD. A major part of the
upgrade project is a Gas Compression & Reinjection (GCR) project and the installation of new
Infrastructure Pipelines & Manifolds (IPM) to
provide the means to interface with or ‘tie-into’ the
already upgraded facilities. CPCL have been involved
with this project since October 2004, primarily as a
sub supplier working with a local contractor acting
as their project manager installing more the $1M
US worth of equipment. During this period we have
steadily formed a relationship with the client and
this resulted in them appointing us to supply ad-hoc
technical support to their operations and projects
department for the completion of the new works.
Owing to the success of our team working on
Lot "A" of the BTC Pipeline, we have now been
awarded a CIPS Survey for Lot "B". This section
is 465 KM long and runs through the Eastern
Mountains of Turkey close to the Cities of
Erzerum, Erzincan and Sivas. Our Multinational
team are working 7 days a week to meet the
clients objective, which is completion before the
Winter snow arrive. To date we have completed
over 150 KM in 10 days and expect to
complete in a further 20 days
BTC Pipeline
We are completing a CIPS Survey to 278 km of
the Baku-Tiblisi-Ceyan pipeline in Turkey for the
operating company. This work is ongoing and
data is being regularly collected at a rate of 1015 KM per day. This survey is being scheduled
for completion before mid October as the winter
weather conditions in the region will prevent
access to the high altitude areas of the route
after this date.
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External Corrosion Direct Assessment (ECDA) Surveys
& Monitoring Techniques
This survey records Pipeline "ON" and "OFF"
potentials at regular intervals of 1 metre which
are achieved by the installation of our
CATH_TECH GPS synchronised current
interrupters at the Transformer Rectifiers on a
cycle of 0.8 seconds "ON" and 0.2 seconds
"OFF". Readings are recorded along the pipeline
route with our own HEXCORDER Graphica
instrument which gives full synchronisation via
the GPS network with the interruption cycle of
the current interrupters. A second HEXCORDER
is installed as a Static Logger to correlate any
stray current interference found on the pipeline.
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HEAD OFFICE
Cathodic 6pp - Single Pages
3/3/08
10:18
Page 6
Cathodic Protection Co. Limited
Venture Way
Grantham
Lincolnshire
NG31 7XS
United Kingdom
Tel: + 44 (0)1476 590666
Fax: + 44 (0)1476 570605
UK BRANCH OFFICE
Email: cpc@cathodic.co.uk
Cathodic Protection Co. Limited
Electra House
Crewe Business Park
Crewe
Cheshire
CW1 6GL
United Kingdom
ABU DHABI OFFICE
Tel: + 44 (0)1270 500440
Cathodic Protection Co. Limited
Abu Dhabi Branch Office
P.O. Box 52937
Abu Dhabi
United Arab Emirates
Tel: + 971 2 671 6895
Fax: + 971 2 674 2342
Email: cathodic@emirates.net.ae
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