The corrosiveness of liquid is a threat to measuring instruments, and only a few types of flowmeters, such as clamp-on ultrasonic flowmeters, are less corrosive. Corrosive liquids directly contact the flowmeter with the liquid mainly because of the corrosiveness of the parts, which damages them and cannot be used. For example, the corrosiveness causes damage to the diaphragm of the differential pressure transmitter, and the leakage of silicone oil makes it completely ineffective. Electromagnetic flowmeter electrodes cause liquid leakage due to corrosiveness, resulting in damage to the excitation coil. Therefore, the selection of the electrode and lining material is extremely important compared to the electromagnetic flowmeter.
Electromagnetic flowmeter commonly used electrode materials include acid-resistant steel, molybdenum-containing acid-resistant steel, Hastelloy, titanium, tantalum, platinum, platinum-iridium alloy, etc. Acid-resistant steel and molybdenum-containing acid-resistant steel are mainly used for domestic industrial water, raw water, sewage, waste water, and weakly corrosive acid and alkali solutions such as dilute acid and dilute alkali. The price is the lowest; Hastelloy is non-oxidizing to low-concentration hydrochloric acid, etc. Suitable for acid and non-oxidizing hydrochloric acid, but not suitable for oxidizing acids such as nitric acid; the corrosion resistance of titanium is slightly better than that of acid-resistant steel, and it has excellent corrosion resistance to chlorides, hypochlorites, seawater, and oxidation to nitric acid at room temperature. Reducing acids such as hydrochloric acid and sulfuric acid are not applicable; tantalum has superior corrosion resistance similar to glass. It is suitable for most acids except for a small amount of acid such as hydrofluoric acid and fuming sulfuric acid. Sodium oxide and other lye are not applicable; platinum, platinum-iridium alloys have corrosion resistance to almost all acids and alkalis, aqua regia, ammonium salt and a few liquids are not applicable, the disadvantage is that they are expensive.
Common lining materials include neoprene, polyurethane rubber, polytetrafluoroethylene, hexafluoropropylene, polyethylene and so on. Among them, the good corrosion resistance is polytetrafluoroethylene, which is resistant to hydrochloric acid, sulfuric acid, aqua regia, and concentrated alkali solutions; neoprene is suitable for tap water, industrial water and other low-concentration acid and alkali solutions; polyurethane rubber is good It has poor abrasion resistance, acid and alkali resistance, and is suitable for pulp, mineral pulp and other slurries.