A new generation of reference electrode: pl2 polarization probe

1、 Functional features and advantages

1. When the polarization test probe is placed in the same soil medium as the buried pipeline, close the switch K, and the steel plate at the bottom of the probe will pass through the wire and connect with the buried pipeline through the test pile and introduce polarization, so that the steel plate 9 and the buried pipeline have the same polarization potential. That is to say, steel plate 9 is equivalent to the simulated test piece, which solves the problem that the pipeline can not be measured without exposed iron.

2. Through the salt bridge hole 6, the polarization potential of steel plate (also buried pipeline) can be easily measured by high resistance voltmeter with copper / copper sulfate or zinc reference electrode built in cylinder 1. Because the pipe wall of Yanqiao hole 6 is very thin and the distance between semi permeable membrane microporous ceramics and steel plate is very close, the IR drop caused by this is very small, which can be completely ignored in engineering, that is, the measured electrode potential is the real polarization potential on the pipeline. In order to make the reference electrode as close as possible to the research electrode, so as to eliminate the IR drop and make the potential measurement as real as possible. So pl2 polarization probe can effectively suppress IR drop.

3. Because the salt bridge hole is very small and surrounded by steel plate, when the ratio of steel plate area to salt bridge hole is large enough, the stray interference current will be completely shielded by the steel plate without affecting the potential measurement. This structure makes the measured value of pl2 polarization probe very stable, smooth and accurate in serious interference area, and is not affected by interference.

4. Disconnect the connection switch K between the steel plate and the pipeline, that is to say, the input of polarization current is cut off. At this time, it is very convenient to carry out "power off measurement" on this device. Because pl2 can effectively eliminate the IR drop, whether the power is cut off has little effect on the measurement results. This function of pl2 is mainly used for research.

It should be pointed out that when copper sulfate electrode is used for internal reference of polarization probe, the potential drift may be caused by the chemical adsorption of copper ion. However, after years of continuous improvement of pl2 structure and repeated consideration of the size of each part, and the actual use of many domestic users, universities and scientific research institutes, this problem has little impact on the buried pl2 polarization probe, but it has no effect on the portable probe. Of course, zinc electrode and calomel electrode can be selected for internal reference. In order to meet different requirements, pl2 also has calomel reference type and zinc reference type polarization test probe. Customers can choose according to design requirements and needs.

2、 Main parameters (taking copper sulfate type as an example)

1. Working current density of electrode: < 5 μ A / cm 2;

2. Potential drift: < 10 MV;

3. Electrode internal resistance: < 100 Ω;

4. Electrode temperature coefficient: 1.0mv / ℃;

5. Electrode material: high purity electrolytic copper;

6. Design life: 20 years.

3、 Typical application analysis

Corrosion was found in the operation of a pipeline with impressed current cathodic protection in CNPC. Through field measurement of portable copper sulfate reference electrode (without simulation test piece), it was found that the protection potential was greatly higher than-0.85v, including charged potential of -1.62v and power-off potential of -0.94v. Stray current interference was judged on site, and IR drop was superimposed in the data. The results showed that the polarization potential was only - 0.76 to - 0.78 V, which did not reach the minimum protection potential.

1. When k of the polarization probe is disconnected (i.e. the steel plate is powered off), the potential difference between the internal reference and the portable reference is 0, which indicates that both of the reference devices work normally and have good consistency. The test data will be reliable and comparable.

2. The result of portable reference charged measurement is obviously superimposed with a large IR drop and is not correct.

3. No matter whether the pipeline is cut off or not, the data hardly changes. This fully shows that pl2 polarization probe has a strong ability to resist stray interference and eliminate IR drop, and the measurement results are true and reliable. This result also reveals that the cathodic protection of the pipeline is not up to standard, which is not up to - 0.85v, which may be the main reason for the pipeline corrosion.

4. The measured value is -0.94v by portable reference power-off, which shows that the off potential still contains about 0.2 (0.18) V IR drop component. This is basically consistent with the result of measurement item 5, that is, the data displayed in measurement 5 is the superimposed IR drop in the off potential of the portable reference electrode. The cause of IR drop of off potential needs further study. This example once again vividly shows that in some cases, the measurement may not get correct results even if the power is cut off by using the common reference electrode. It seems to be up to standard, but in fact it is false. If we accept these data, it will mislead the normal operation of cathodic protection.

4、 Impact

Compared with the similar products abroad, pl2 has the advantages of novel structure, good stability, firmness and reliability, long service life, easy to carry and field application. The reference potential is measured and marked by CSE (copper / copper sulfate reference electrode), which is commonly used in soil cathodic protection projects in China (SCE is commonly used in imported polarization probes), so pl2 is a new generation of reference electrode more suitable for China's national conditions 。 In order to adapt to the rapid development of pipeline coating technology progress, solve the problem of difficult to find the leakage point, at the same time, to effectively suppress the stray current interference, the maximum elimination of IR drop. It will be an inevitable trend to replace the traditional reference electrode with a polarization probe.

Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing corrosion protection, cathodic protection technology, engineering design, installation and technical services.