Measures against Fluid Corrosion in Flow Measurement

Measures for fluid corrosion in flow measurement (regular replacement of instruments) Corrosion of metals by corrosive media is varied. Some corrosion speeds are very fast, that is, general corrosion, and some corrosion is slight and the speed is very slow. That is, localized corrosion. When selecting an instrument, it should be analyzed according to the specific situation, and then make a decision. For example, compressed air and water are generally considered to be corrosion-free, but in fact they are not. Since the concentration of nitrogen oxides in the urban atmosphere is generally high, when After it is absorbed by the condensate in the compressed air, the condensate is acidic, which has mild corrosion on carbon steel materials. This situation is more serious in sulfuric acid plants, nitric acid plants, chlor-alkali plants and other plant areas. Of course, At this time, in addition to dilute nitric acid, there may be sulfuric acid, hydrochloric acid, etc. in the compressed air. The situation of water is similar, especially river water, because it contains a variety of ions, it also corrodes carbon steel. Under this condition The used instrument will also show signs of corrosion after a few years. For example, it is found that the surface of the carbon steel ring chamber in the flow throttling device that is in contact with the fluid is corroded and becomes pitted. Great changes. And the inner wall of the front and rear straight pipe sections has also become uneven. This situation does not meet the requirements of the verification regulations, and it is difficult to guarantee the accuracy of the original instrument. At this time, a proposition arises, that is, whether the design and selection should be throttling The annular chamber and the front and rear straight pipe sections in the device are also made of stainless steel? Of course, if the material is changed to stainless steel, the corrosion problem of the annular chamber and the straight pipe section will definitely be solved, but at the same time the investment will increase. And the increase in investment is related to the diameter of the pipe. If If the nominal diameter is large, the increase in investment is not a small number. Therefore, the decision-making should be based on the measurement accuracy requirements of specific measurement points, corrosion severity, expected life expectancy, and budgetary capacity. Measurement accuracy requirements are not high (such as for process monitoring and control), mild corrosion, carbon steel material life expectancy of more than 10 years, after changing to stainless steel, the investment will increase more, then, it is better to wait for the ring chamber to be corroded and cannot continue When in use, replace the whole or damaged part of the throttling device. Avoiding the heavy and the light is to choose the measurement plan reasonably on the basis of a deep understanding of the process flow and the characteristics of the relevant media, and the purpose of measuring or controlling the production process can also be achieved. , avoid highly corrosive parts, and choose less corrosive parts, or even change the type of adjusted parameters. For example (if feasible) adjust the flow constant value adjustment system with liquid level adjustment or other suitable variable adjustments Instead, so as to avoid the problem of corrosion resistance of flow measuring instruments. For example, the flow of sewage entering sewage treatment plants is generally measured in order to control the total amount of pollutant discharge. Sewage is generally acidic or alkaline, and correspondingly Add an appropriate amount of alkali or acid to neutralize. Then, considering the corrosion of the sewage on the flow meter, of course it is better to choose the flow detection point after neutralization. The flow measurement of raw gas in steel plants is similar. Raw gas often contains A certain amount of sulfur dioxide, this gas is not very corrosive when it is dry, but after the raw gas leaves the kiln, with the increase of the transportation distance, the temperature of the gas gradually decreases, the humidity increases correspondingly, and soon condenses It is highly corrosive. When considering the installation location of the gas flow measuring instrument, it should of course be selected before the gas condenses. Choose a gauge with corrosion-resistant properties

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