How to Select a Right Magnetic Flow Meter?
Nowadays, the magnetic flow meter (electromagnetic flow meter) has been widely applied to measuring of industrial sewage or wastewater. With a high precision and a long service life, the magnetic flow meter is the top choice for the environmental measuring industry. To choose the correct magnetic flow meter can five fuller play to the magnetic flow meter for specific purposes. Generally, the selection of the magnetic flow meter is based on the following factors including chemical attributes of the fluid medium, pipeline diameter, flow range, lining material, electrode material and output signal.
Measurable fluid medium
According to the working principle of the magnetic flow meter, the fluid measured by the magnetic flow meter must be conductive. To be strict, any fluid whose conductivity is larger than 5μ/cm, excluding the high-temperature fluid, can be measured by the magnetic flow meter. Therefore, the non-conductive gases, including steam, oils, and acetone, should not be measured using the magnetic flow meter.
Integrated or split type mag flow meter
The magnetic flow meter can be divided into the integrated type and the split type. The integrated type is generally applied to favorable environments. The sensor and converter of the integrated electromagnetic flow meter are integrated, while the sensor and converter of the split type are separated from each other. And the split type magnetic flow meter is generally applied to conditions which are not suitable for reading. For example, when the environmental temperature is too high, the pipe vibration is huge, the onsite environment can cause corrosion, and the magnetic flow meter is installed at a high altitude, the split magnetic flow meter will be a better choice. ATO split type magnetic flow meter is equipped with 10m cable line to connect the converter to ensure the converter at a suitable environment.
Under general conditions, the reducing pipe is not selected under the prerequisite that the acceptable flow rate within the flowmeter pipe falls within the range of 0.3m/s to 10m/s. The setting is applicable to the newly-designed project. Selection of the flow rate should consider not only the current working situations but also the operation of the equipment at a full load. However, the diameter of the mag flow meter to be selected might be different from the processing pipe diameter under the following two conditions.
The flow rate within the pipe is slow, but the processing flow is relatively stable. In order to satisfy the meter’s requirement of the flow range, the flow rate is accelerated partially in the flowmeter. The flow meter diameter is smaller than the processing pipe caliber, and the reducing pipe in the front and at the back of the reducer.
In terms of the magnetic flow meter with a large caliber, the larger the caliber is, the higher the price is. When the flow rate within the flow is slow, and the processing parameters are stable, the flowmeter with a small caliber can be chosen. This can not only ensure the flowmeter to function under a good condition, but also reduce the investment cost.
Electrode materials include 316L electrode, tantalum electrode, HC electrode, platinum electrode, etc. The magnetic flow meter should choose electrode materials according to corrosiveness of the measured fluid. See the table below and there are some common electrode materials and its applications.
|Stainless steel SUS316||Applicable in water, sewage and other weak corrosive fluids, widely used in industries of petrol, chemistry, carbamide industry, etc.|
|Stainless steel covered with tungsten carbide||Applicable in fluids of no corrosive and high abrasion.|
|Hastelloy B (HB)||Strongcorrosion resistance to hydrochloric acid of any concentration which is below boiling point, also resistible against vitriol, phosphate, hydrofluoricacid, organic acid, etc. non-oxidized acid, alkali and non-oxidized salt solution.|
|Hastelloy C (HC)||Resistant against oxidizing acid corrosion such as nitric acid, mixed acid, as well as oxidizing salt such as Fe3+, Cu2+ or other fluid containing oxidizer like Hypochlorite solution, sea water.|
|Titanium (Ti)||Applicable in seawater, and kinds of chloride, hypochlorite salt, oxidizing acid (including fuming nitric acid), organic acid, alkali etc. Not resistant to a pure reducing acid (such as sulphuric acid, hydrochloric acid) corrosion. But if acid contains oxidizer (such as Fe3+, Cu2+), the corrosion will be greatly reduced.|
|Ta||In addition to hydrofluoric acid, fuming sulfuric acid, alkali, it can almost be anti-corrosion of all the chemicals, including boiling hydrochloric acid.|
|Platinum-iridium||Almost be applicable in all chemical media except for aqua fortis, ammonium salt.|
Ground ring materials
The ground ring materials and the electrode materials should be the same, and the materials are usually characterized by corrosion resistance similar to the pipe materials.
The liner materials can be chosen according to corrosiveness, abrasion and temperature of the measured medium. According to characteristics of the media, PO, rubber, Teflon, polyurethane, or ceramic lining can be adopted. See the table below for more details.
|Lining Materials||Main Performance||Applications|
|Teflon (PTFE/F4)||1. The most steady material in plastics which is resistible to boiling hydrochloric acid, sulfuric acid, aqua regia,as well as strong alkali and organic solutions.
2. Not perfect in abrasion resistance.
|Applicable in strong corrosive fluids such as strong acid and alkali.|
|PFA (Perfluoroalkoxy)||1. The same abrasion resistance as PTFE.
2. Having strong ability of load pressure resistance.
|Applicable in state of strong load pressure.|
|F46||1. The similar corrosion resistance to acid, alkali, and salt with PTFE.
2. Better resistance to abrasion and load pressure than PTFE.
|Same applications as PTFE.|
|Neoprene (chloroprene rubber/CR)||1. Good elasticity, retractility and abrasion resistance.
2. Resistance to corrosion of low aicd, lkali and salt but not for oxidation media.
|Water, sewage, sea water and slurry, mineral serosity with low abrasion.|
|Polyurethane||1. Good abrasion-resistance performance.
2. Not be perfect in acid/alkali resisitance.
3. Can't be used for water mixed with organic impregnants.
|Applicable in mineral serosity, slurry and coal slurry with high abrasion.|