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Technologies Laboratories developed a system to assess the effectiveness
of cathodic protection in dynamic stray current conditions (called
“Coupon Monitoring for Cathodic Protection Optimization”
(CMCPO)). The approach consists of optimizing the performance
of the CP system in response to the real-time changes in the
IR-drop-free potentials of the protected structure. Monitoring
the IR-drop free polarization potentials is accomplished through
the use of multiple Coupon
Test Station (CTSs), buried in close proximity to the buried
pipeline. At the heart of the system is an algorithm which processes
the data collected from each CTS and stored in the data storage
module similar to CM
3400. On the basis of the data and the chosen protection
criterion (100 mV of polarization), the CMCPO categorizes the
conditions as those with ‘no protection’ or ‘minimal,
insufficient, adequate protection’; another category is
the ‘overprotection’. Based on the assessment, the
system (if used in active (‘control’) mode) issues
a command to the remotely controlled rectifier to change the
output according to the corrosion conditions. This system provides
the ability to monitor pipelines in stray current areas more
accurately than ever before. Monitoring can be performed on
a periodic basis or setup as a continuous system with remote
access.
The monitoring system has an option of being
used as a fully automated remote control system to achieve
CP optimization via controlling the output of specially equipped
rectifiers. The CMCPO system was tested for a period of almost
two years in the field under conditions of dynamic DC currents
of significant magnitudes. Upon completion of the trials,
the analysis of the CMCPO operation has shown that the benefits
of the CMCPO system were tremendous. Shown in Figure 2 are
the changes in the CP categories before and after the installation
of the system (the operation of the system and the in-depth
analysis of the data are given in the article
presented at NACExpo 2002).
Click graphic to expand
to full size
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Figure 2. CMCPO BENEFITS: Cathodic protection
efficiency before (round bars) and after (square bars) installation
of CMCPO system
A semi-quantitative evaluation of the extension
of service life of the monitored structure (based on a real-life
corrosion data) shows that is some instances the operation
of the CMCPO in active mode (‘remote control’)
would reduce the wall penetration from 90% over a 30-year
span to a mere 2%, a 45-fold reduction!
The US Patent Office has approved the application
for a patent by the developers of the system (Mark
Yunovich and Neil
Thompson).
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