中文(简体) Although there are many methods to measure the metal plate corrosion of brazed plate heat exchanger, few methods can be used in the production process. At present, resistance method, linear polarization method, chemical method and ultrasonic thickness measurement method are widely used.
Resistance method is a method to measure metal corrosion. Its principle is that the change of cross section of metal components after corrosion leads to the increase of resistance. The measuring instrument manufactured according to this principle is called resistance probe. It consists of probe and measuring instrument. After the sample is processed and contacted with the probe, the corrosion rate can be directly read out on the measuring instrument.
The advantages of resistance method are not affected by corrosive environment, simple operation, continuous measurement and recording of corrosion rate, and high sensitivity. The disadvantage is that the processing requirements of the test piece are strict, and the local corrosion characteristics cannot be measured. If the corrosion product is a conductor, there will be great error.
The basic principle of linear polarization method is, Near the free corrosion potential of metal (in the range of about 10-20 MV) there is a linear relationship between the applied current and the generated potential change, and the linear slope is inversely proportional to the corrosion current. The linear polarization method can sensitively measure the instantaneous corrosion rate and can be used for continuous detection and field monitoring. Its measurement range is very wide. Its disadvantage is that it is only suitable for the corrosion system composed of metal electrolyte and the measurement accuracy is not high.
Except ion selective electrode method and hydrogen probe method, chemical method is basically solution analysis method.
Solution analysis is to estimate the corrosion rate by measuring the change of the concentration of corroded metal ions in the corrosion medium. The commonly used chemical analysis methods are volumetric method, colorimetry and polarography. This method is not applicable when the corrosion products are insoluble or the corrosion rate changes with time.
Ion selective electrode method is a method that uses ion selective electrode to determine the change of ion content. Ion selective electrode is an indicator electrode for determining the activity of specific ions in solution by potentiometry. As long as there is a suitable ion selective electrode, the content change of corrosion ions in corrosion medium can be determined. This method has the advantages of convenient operation, simple instrument, fast and continuous determination.
Hydrogen probe method is a method to calculate metal corrosion rate by measuring the hydrogen content of corrosion products. Generally, it is only applicable to the corrosion system in which the cathode process is hydrogen evolution.
Ultrasonic thickness measurement is to measure the wall thickness of equipment with ultrasonic thickness gauge to understand the corrosion. It can detect the running equipment at any time without damaging the equipment, but the accuracy of the instrument has a great impact on the measurement accuracy.
