Study at the Application of Flow Switches in the Corrosive Liquid

Study at the Application of Flow Switches in the Corrosive Liquid
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

In the fields of electric power, energy, chemical industry, medicine and so on, the corrosion problem of flow switch used for fluid monitoring has always been a headache for users. Some users, installed the newly purchased flow switch, have been corroded in less than two or three months, the switch action has become less sensitive, and the electrical components are also rusty, so the flow switch can not send out alarm signal when the fluid is cut off, and can not play the role of protecting the machine and equipment. In view of the importance of fluid detection to machinery and equipment, many users have an urgent demand for high-strength corrosion-resistant flow switches.

GE-313 Teflon PTFE Plastic Paddle Flow Switch

This flow switch is produced by teflon plastic material with a long paddle, combats the problems of ...

2. Performance of stainless steel flow switch in corrosive fluids

2.1 304 stainless steel flow switch

At present, 304 stainless steel and 316L stainless steel are the main materials used for flow switch manufacturing in the market, of which the price of 304 stainless steel is relatively low compared with 316L, but 304 stainless steel can not resist the slight corrosive fluid such as sea water, let alone those strong acids and bases. Therefore, it can be determined that the flow switch made of 304 stainless steel can not be used in corrosive fluid basically, and can only be used in pure water flow for fluid detection.

V10SS Paddle Flow Switch with Stainless Steel flow switches

The V10SS flow switch utilizes a rugged, hermetically sealed reed switch which is encapsulated in a ...

2.2 316L stainless steel flow switch

The corrosion resistance of 316L stainless steel is better than that of 304 stainless steel, and it has good corrosion resistance in the process of papermaking. Moreover, 316L stainless steel is also resistant to marine and corrosive industrial atmospheric erosion. However, for many years, it has been found that 316 is not really "stainless", they will be corroded, perforated and broken . Moreover, 316L stainless steel has high price and less demand of users, so the cost of flow switch will be very high.

2.3 Special stainless steel for acid and alkali resistant

If a strong acid-resistant stainless steel flow switch is required, it should be made of special acid-resistant stainless steel. However, its materials are difficult to buy, and its price is extremely expensive. There is no flow switch of such materials on the market, so this article does not discuss the special acid-resistant stainless steel flow switch.

3. Performance of plastic materials in corrosive fluids

3.1 flow switch with common plastic material

At present, the flow switch of plastic material in the market is mainly made of PA66 nylon plastic, which is popular with users because of its low price. However, it is found that the comprehensive mechanical properties of PA66 and its composite materials in chemical media are significantly reduced ; moreover, nylon materials can not withstand the corrosion of strong acid and strong alkali, such as the contact between nylon plastic flow switch and concentrated sulfuric acid, which is almost instantaneously dissolved in concentrated sulfuric acid, and the flow switch of nylon plastic materials is instantaneously melted into powder. Therefore, nylon material flow switch can be used in ordinary slightly corrosive fluid, but in high-strength corrosive environment, its performance is worrying.

3.2 Teflon material flow switch

At present, the manufacturers of Teflon-resistant corrosion-resistant flow switches are only two companies, such as PEECO in the US and A.YITE TECH in Hong Kong.

The Teflon flow switch produced by PEECO is manufactured by lathe machining, similar to the manufacturing method of stainless steel flow switch. Since the bearing of the target is made of 440C stainless steel, the stainless steel bearing of this target activity becomes a short plate with corrosion resistance. Therefore, its corrosion resistance is not very satisfactory; and its price is as high as hundreds of dollars, the average user can not afford its high price.

GE-313 series Teflon flow switches are manufactured by A.YITE TECH Hong Kong,  are made of composited materials, which can completely isolate all metal or electrical parts that may be corroded from liquid through multiple injection molding of important parts. All parts in contact with the fluid are made of high-strength and corrosion-resistant Teflon composite plastics. All sensing devices are injected into Teflon plastic materials, so they can be used for water flow monitoring of various corrosive fluids. Moreover, because it is a mass injection manufacturing, its price is low, the price of nearly $30 can be accepted by the majority of users, so this paper focuses on its research.

The GE-313 Teflon flow switch manufactured by A.YITE TECH in Hong Kong. does not contain corrugated pipes that are prone to failure. After testing, the corrosion resistance of this water flow switch is much higher than that of ordinary water flow switches; and at 99.99 Working in concentrated sulfuric acid for more than one year, there will be no problems.

Because of adopting the Teflon composite, the flow switch is virtually immune to chemical corrosion, can withstand all of the strong acids (including aqua regia) and strong oxidants except molten alkali metal, fluoridated media and sodium hydroxide above 300 °C. The action of reducing agents and various organic solvents protects the parts from any kind of chemical attack. Widely used in electric power, chemical industry, acid production, alkali production, smelting, rare earth, pesticides, dyes, medicine, paper, electroplating, electrolysis, pickling, radio, chemical foil, scientific research institutions, national defense industry, etc., it can be exposed to any concentration Acidic, alkaline, oily, rare and valuable liquids, toxic liquids, volatile corrosive chemical fluid media.

4. Conclusion

After a series of comparisons, the flow switches of 304 and 316L stainless steel performed poorly in corrosive fluids; the nylon plastic flow switch performance was unsatisfactory; the PEECO Teflon flow switch made by lathe machining performed well, but price is too high to meet the user condition; GE-313 Teflon flow switch,  manufactured by injection molding, is not only cheap, but also has good performance in corrosion resistance, suitable for sulfuric acid plants, paper mills, chemical plants, sewage. Corrosive fluids such as treatment plants, printing plants, printing and dyeing plants, electroplating plants, pharmaceutical plants, etc., GE-313 flow switch is  the best choice for fluid monitoring in corrosive fluids.