1. Development Background
With more and more focus paid on the metal corrosion and protection measures, the cathode protection technology is given with guidance standards on the national level especially for the buried steel pipeline and port engineering facilities, also, some mandatory requirements are made for cathode protection of ships and other equipment during construction.
However, the anti-corrosion measures are not much satisfactory during the true operation. Due to the undeveloped technology of testing equipment, the current testing data system is not complete, objective, or scientific, which hinders the effective work of the cathode protection to the metal structures.
The system mainly consists of the following parts:
ⅰ.Intelligent potential detector
ⅱ.Electronic test pile
ⅲ.Long effective reference electrode
ⅳ.Cathode protection test piece
ⅴ.Connection cable 2. System Principle
The tester is provided with modern micro-electronic technology, together with the outage potential measurement technical to eliminate the impact of the IR reduction to the measurement of the cathode protection potential.
The intelligent ester can work and keep many parameters like power-on/off potential, and AC interference voltage and measurement time automatically, and discovery the stray current in advance so as to solve some problems.
The tester is simply and conveniently operated, featuring accurate and reliable measuring results and strong anti-interference capacity, capable of storing and playing back 200 groups of measuring data. 3. Cathode Protection Intelligent Detection System
3.1 Intelligent potential detector
3.1.1 Measurement scope
ON potential -3000 ~ 3000mV, OFF potential -3000 ~ 3000mV, AC inference 0 ~ 50V
3.1.2 Measurement accuracy
ON potential 1mV，OFF potential 1mV，AC inference 0.1V
3.1.3 Measurement parameters
ON potential，OFF potential，AC inference，natural potential，measurement time
3.1.4 Other parameters
Anti-AC inference: 50V，Storage groups: 200 groups，Charging voltage: 5V，Working current: 500mA，Use time: >10h，Automated OFF time: 2 min if no operation
3.1.5 Measurement method
The detector is used to for polarization and depolarization of the test piles as per the 3s-on and 1s-off method as specified in NACE RP-0169.
According to NACE TM0497, the best measuring time for OFF potential is 0.5~3s after power outage. Considering the potential of the polarization test pile is damping, the OFF potential at 0.5s after power outage shall be measured.
When the tester is connected with OFF potential, the AC inference shall be shielded to reduce the impact of AC inference to the measurement results and guarantee the accuracy of measurement data.
Significance of measurement of OFF potential and judgment criteria
The cathode protection potential is an important parameter of the anti-corrosion system. The ON potential is used for daily maintenance and measurement of the pipeline while the OFF potential is used as the judgment criteria of catholic protection principles. The OFF potential apparently shows whether the pipeline is under sufficient catholic protection.
The standard that the OFF potential is negative to -850mv and positive to -1200mv is one of the standards to judge whether the pipeline is under good cathode protection.
If the above standard cannot be met, the standard that the cathode protection potential is negative to the natural potential for over 100mv is another standard to judge if the pipeline is under good cathode protection.
3.1.5.1 The detector can realize the daily detection for the pipeline true protection potential, which eliminate the difficulty of measuring the pipeline true protection potential and also the high cost. Therefore, the operator can rapidly know the true condition of the pipeline, handle the pipeline without proper protection, as a result the pipeline service life is extended and the accidents caused by poor protection can be avoided.
3.1.5.2 The simple and rapid detection of pipeline true potential is realized, breaking the shortcomings of the existing detection method.
3.1.5.3 The information of detection data, time and pile No. is stored automatically, the manual copying is not necessary, meanwhile the data fraud made by the inspection worker is eliminated.
3.1.5.4 The ON potential, disturbance voltage and true potential are measured at the same time, which shows the protection status of the pipeline truly.
3.1.5.5 The data is imported into computer and encrypted automatically, reducing the time and cost of manual copying and eliminating the data fraud.
3.2 Electronic test pile
LK-004 RFID is a kind of new device used for standard detection port of the cathode protection system and information storage of electronic test pile, and it is mainly used for detection of cathode protection potential.
Steel test pile is an important auxiliary facility for data and anti-corrosion detection during daily maintenance.
3.3 Long effective copper sulphate reference electrode
The reference electrode is an important part of the cathode protection system, which can be used not only for the potential of the protected structures, but also as the signal source for automatic control of potential, the saturated copper sulfate is widely applied for the cathode protection of buried pipeline, underground cable and other metal structures.
3.4 Cathode protection test piece
The cathode protection test piece is the metal test piece representing pipeline at the testing position for the cathode protection detection. An insulation test wire connecting with the test piece is introduced to the ground and connected with the pipeline testing wore during the normal operation period. The test pile receives the cathode protection current, and the testing position here refers to the pipeline.
The connection is available to be cut off for detecting the polarization potential of the test piece. In order to detect the OFF potential, the time for disconnection shall be as short as possible in case of excessive depolarization.
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