Electrical Probes EMT-CP

Description

The Electrical Probes use the principle that the resistance increases due to the reduction of the cross section during the corrosion thinning of the metal sample. It calculates the corrosion rate by measuring the resistance change of metal samples in the corrosion process.

The Electrical Probes, like the corrosion coupon, is a corrosion monitoring technology during intervention. It is different from the weight-loss coupon method. Resistance probe technology does not require excavation and weighing. Because the temperature has an effect on the test resistance value. Therefore, the resistance probe test principle uses the reference element to compensate the temperature of the elements of the test piece. This refers to the protection of components against corrosion with anti-corrosion materials such as coatings. The resistance probe exposed to corrosive environment is the test piece element.
The resistance probe is generally filiform or flake. Among them, the sensitivity of filiform is higher than that of flake. When we apply a constant current to a wire. Or when the metal resistance wire has corrossion. The cross-sectional area of the wire is reduced. The length of the wire remains unchanged. The change of wire diameter is obtained by the change of voltage at both ends of the wire. In this way, the corrosion rate of the resistance probe can be calculated. In resistance probe measurement, temperature compensation is an important factor affecting the monitoring accuracy.

The advantages of  Electrical Probes are:

1. Resistance probe has a wide range of applications, including gas phase, liquid phase, solid phase and flowing particles;
2. It is simple and fast, without sampling in the monitoring process, and can realize real-time data collection and real-time data analysis;
3. Compared with the weight loss method, the response speed is faster.

The disadvantages of  Electrical Probes are:

1. Due to the non-uniformity of actual pipeline corrosion. For a single probe, its corrosion characteristics are inconsistent with the amount of corrosion on the inner wall of the monitored pipeline to a certain extent. This difference is more obvious under the conditions of high-speed fluid and solid impurities;
2. Under the existing technical conditions, the cross section of the probe is processed very thin. This results in a short service life of the probe. Especially under the condition of high corrosion rate, it is not suitable to use resistance probe;
3. We cannot monitor local corrosion;
4. Compared with inductive probe, the sensitivity is low. Therefore, it cannot respond to the rapid changes of external corrosion conditions;
5. Corrosion products or oxide scales with conductivity gather on the surface of the probe. This will affect the measurement results of the probe. For example, in the medium containing sulfide, ferrous sulfide (FES) produced by corrosion has conductivity. This will also affect the actual corrosion rate;
6. The material of the probe shall be consistent with that of the pipe.

Principle introduction:

In corrosive media, the metal wire as a measuring element has corrossion. The wire length remains unchanged, the diameter decreases, and the resistance increases. The corrosion thinning amount of metal wire can be converted by measuring the change of resistance. When the material of the metal wire used is the same as that of the measuring equipment. The corrosion rate of metal wire can approximately represent the corrosion rate of equipment. The Electrical Probes measurement technology are based on the above principle. The establishment of resistance probe measurement method can timely display the corrosion of equipment and pipelines. Operators shall find abnormal corrosion in time. In this way, safety production caused by equipment corrosion can be avoided. Therefore, it is an effective means of corrosion detection.
The corrosion rate measured by resistance probe is based on the linear relationship between the cross-sectional area and the resistance at any time under the premise of constant length of the resistance probe wire. At the same time, in order to eliminate the measurement error caused by temperature, a temperature compensation element is added to the measurement structure.

For example, the cross-sectional area of metal materials with a certain length decreases and the resistance increases after corrosion thinning. So we only need to know the change value of its resistance. We can calculate the thinning amount.

Measuring System:

The resistance probe corrosion monitoring system includes: corrosion resistance probe, fastener, corrosion data collector, connecting cable, data converter, computer and online monitoring software system

High temperature resistance probe probe includes protective cap, measuring element, probe rod and signal interface

Resistance probe

Because the resistivity of metal materials changes with temperature. Therefore, in order to avoid measurement errors caused by medium temperature changes. We usually put a temperature compensation element in the probe rod. Then connect it with the measuring element in series in the circuit. At this time, it can completely eliminate the influence of temperature. The protective cap is sleeved outside the probe to slow down the impact of high-speed medium flow on the probe measuring element. The card slot works to connect and fix with the disassembly device when installing and disassembling the probe.

The key to the development of high temperature Electrical Probes are the sealing of the probe and the insulation of its internal leads. Glass ceramic works as sealing material and sintered at high temperature above 1000 ℃. Then use porcelain bushing to insulate the lead wire in the probe rod. Its connecting parts are all welded by laser. Install the sealed probe in the self-made simulated working condition device. Its condition is 450 ℃, 2.0MPa, sulfur-containing diesel oil. After 72 hours, there was no leakage. The sealing and high temperature resistance of the probe can meet the design requirements.

In addition, in order to improve the pressure resistance, the sealing packing part of the probe a spiral inner sleeve base. The measuring elements are filaments.

Compared with the sheet probe, it has the following advantages:

First, it has a long service life. Second, the surface of the filiform measuring element is relatively uniform. Therefore, it is not easy to produce edge effect like sheet measuring elements. From the perspective of use and installation, the probe has two forms: pressure removable and flange. Generally speaking, the former is applicable to the environment where the pipeline pressure is less than 2.0MPa. The latter is applicable to the environment where the pipeline pressure is greater than 2.0MPa.

Monitor

1. Remote acquisition, amplification and digital conversion of weak signals: petrochemical equipment operating above 300 ℃ has potential dangers due to corrosion, and the on-site test should be far away from the dangerous area. Resistance probe tester known to people in the past. (including er8000 imported in the early stage and domestically developed). The lead between it and the probe is very short, only 1~2m. In order to avoid operating in high temperature area, rpm-1511 instrument is designed with independent differential amplification and filter noise reduction technology of measuring element and temperature compensation element. This makes the measuring lead more than 50m. It also makes it possible for one instrument to measure multiple probes. The original signal is collected and amplified for analog-to-digital conversion, and the single-chip microcomputer completes the operation, display and storage.
2. Long distance transmission of digital signals, design of computer software system: to carry out real-time online measurement, the monitor must have the functions of automatic signal acquisition and transmission to the monitoring room at the same time. It equips the computers with RS-232 standard communication interface. But its transmission distance is only 15m. This cannot meet the requirements for industrial sites.

Note:

In order to extend the transmission distance, the RS-485 interface module is connected between the field monitor and the RS-232 of the computer in the monitoring room. The corresponding circuit max487 is also designed in the monitor. This makes the original signal transmission in the form of potential into the form of current loop transmission. Therefore, the transmission distance reaches 1200m, which meets the needs of the site. The design of computer software system also need for online measurement. Visual basic software platform is work to compile the monitoring program of corrosion online monitoring system. This realizes the requirements of clear interface, simple operation and standardized data management.

Application Prospect

Electrical Probes measurement can track the corrosion behavior of metal surface in real environment. It can also master the corrosion rate and corrosion condition. In this way, we can take in time the corresponding process anti-corrosion measures . The operator shall take measures in time to control the corrosion rate within the required range. The establishment of resistance probe measurement method enables us to timely display the corrosion of equipment and pipelines. At the same time, it can quickly find the abnormal corrosion conditions. This can avoid safety production caused by equipment corrosion. This is an effective means of corrosion detection. The design of data processing software for resistance probe measurement is simple and practical, which can effectively manage probe data. It improves the efficiency of data processing and facilitates the query of corrosion data.
The development and application of resistance probe measurement system enriches the means of corrosion monitoring. It fills this gap and provides favorable technical support for the safe operation of the equipment.

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