Study at the Application of Flow Switches in the Corrosive Liquid
《Technology Outlook 과기전망》 2015-19
Jia Chunna1 Zou Min2
(1.China Huadian Engineering Co.,LTD.，Shanghai 201210 China;
2. Huadian Light Gas Turbine Service Co.,LTD.，Shanghai 201210 China）
Abstract: The GE-313 teflon PTFE flow switch is the best choice in the corrosive liquid by analyzing the character and the performance of stainless steel Flow Switches and plastic flow switches.
Keywords:corrosive fluid; corrosion resisting flow switch; teflon PTFE flow switch; stainless steel flow switch; plastic flow switch
1. Introduction
Corrosion problems in the field of electricity, energy, chemicals, pharmaceuticals, etc., for monitoring fluid flow switch has been a headache for users. Some users, buy a new flow switch, with less than two months, it has been corroded horrendous, switching becomes less sensitive electrical components are rusty, so the flow can not be shut-off switch in the fluid When the alarm signal, it can not play the role of protection equipment. Given the importance of detection of fluid machinery and equipment, many users of high strength corrosion resistant flow switch has urgent needs.
2. Stainless steel flow switch's performance in corrosive fluid
2.1 304 stainless steel flow switch
Currently on the market for stainless steel flow switch made of 304 stainless steel and are mainly 316L stainless steel, 304 stainless steel prices relatively 316L which is relatively low, but 304 even slightly corrosive seawater so fluid can not resist, let alone those of acid and alkali a. Therefore, it can determine the flow switch 304 stainless steel can not be used essentially in corrosive fluid, only for pure water stream fluid testing.
2.2 316L stainless steel flow switch
316L stainless steel corrosion resistance than 304 stainless steel with good corrosion resistance and other properties in the paper production process. 316L stainless steel and is also resistant to aggressive marine and industrial atmosphere erosion. However, over the years it had discovered, 316 is not really "stainless", they will be corrosion, perforation, fracture [1]. Moreover, 316L stainless steel prices relatively high, fewer user demand, so the flow switch cost will be very high.
2.3 Special acid stainless steel
If you require a strong acid-resistant stainless steel flow switch, you should use special acid stainless steel. However, the material is difficult to buy, and the price is extremely expensive, these materials flow switch has not yet appeared on the market, so this acid for special stainless steel flow switch is not discussed.
3. plastic material in a corrosive fluid performance
3.1 ordinary plastic material flow switch
Plastic material currently on the market mainly flow switch PA66 nylon plastic-based, the material because of its low price, loved by the users. However, the study found that the mechanical properties of PA66 and its composite materials in the chemical medium is significantly reduced [2]; and nylon can not withstand acid and alkali corrosion, such as nylon plastic flow switch contact with concentrated sulfuric acid, almost instantly dissolved in concentrated sulfuric acid, nylon plastic material flow switch instantly melt into powder. So nylon flow switch can be used for general slightly corrosive fluid, but in high strength corrosive environment, its performance is worrisome.
3.2 Teflon material flow switch
Manufacturing Teflon corrosion resistant material flow switch manufacturers in the world currently only the United States and Hong Kong Yiyi Te PEECO Company (A.YITE TECH) and other two companies.
Wherein PEECO company's Teflon flow switch is manufactured using the lathe machining, similar to the manufacturing method of stainless steel flow switch. Since the bearing target sheet activities using a 440C stainless steel, so the target sheet activity stainless steel bearing corrosion resistance has become a short board possible. So its corrosion resistance is not very good; and its price up to several hundred dollars, the average user to bear their high prices.
Hong Kong Yiyi Te company's GE-313 series flow switch is the use of Teflon nanocomposite important components through multiple injection molding, so that all may corrode metal or electrical components and the liquid is completely isolated. All parts in contact with the fluid are corrosion resistant high strength Teflon composite plastic, all sensing device all injection molding of plastic material in Teflon, so it can be used for a variety of corrosive fluid flow monitoring. Also, since large quantities of injection molding manufacturing, its low price, almost 30 dollars price can be accepted by the majority of users, this article focuses on them.
Hong Kong Yiyi Te company's GE-313 Teflon flow switch, without easily lead to failure of the bellows, tested and corrosion This water flow switch can be much higher than normal water flow switch; and at 99.99 % concentrated sulfuric acid in work for more than a year without any problems.
As a result of Teflon composite materials, almost free from drugs erosion flow switch, in addition to be able to withstand the molten alkali metal fluoride, a strong acid medium, and above all than 300 ℃ sodium hydroxide (including aqua regia), strong oxidizing agents, reducing agent and various organic solvents, can protect parts from being any kind of chemical corrosion. Widely used in electricity, chemicals, acid, alkali, smelting, rare earth, pesticides, dyes, pharmaceuticals, paper making, electroplating, electrolysis, pickling, radio, foil, research institutions, national defense industry and other industries, can reach any concentration acidic, alkaline, oils, rare and precious liquids, toxic liquid, volatile corrosive chemical fluids.
4. Conclusion
After a series of comparison, 304 and 316L stainless steel flow switch is poor performance in corrosive fluid; nylon plastic flow switch performance is not satisfactory; the lathe machine manufacture of PEECO Teflon flow switch performance is acceptable, but its price is too high, can not meet customer demand; manufactured by the injection molding of GE-313 Teflon flow switch, not only low prices, and with superior corrosion resistance, suitable for sulfuric acid plants, paper mills, chemical plants, sewage processing plants, printing, dyeing, electroplating plants, pharmaceutical plants and other corrosive fluids, is the best choice in the corrosive fluid monitoring fluid.
【reference】
[1] abalone its Nai chloride corrosion in the cooling water system of stainless steel [J] industrial water treatment, 2007,27 (9): 6
Chemical resistance [2] 孙红玲 etc. .PA66 / LGF composites can study [C] 2012, China Engineering Plastics Composites Technology Conference Proceedings, 2012: 96-99