Advantages of fluorine-lined butterfly valves in the modern petrochemical industry

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This post was last edited by shiwendong on 2017-3-15 at 19:01. With the rapid development of the modern petrochemical industry, some fluids used under specific operating conditions are highly corrosive; even stainless steel valves as well as butterfly valves lined with rubber or enamel can no longer meet the requirements. If alloys such as Hastelloy, Monel, or alloy 20 are used as materials for butterfly valves, they contain large amounts of rare metals such as Ni, Cr, Ti, Mo, Nb, and Pt; these metals are limited in supply and therefore expensive. Based on the achievements of modern science and technology, the molecular structure of fluoroplastics contains carbon-fluorine bonds along with their shielding effect, which endows them with excellent corrosion resistance, tolerance to high (low) temperatures, non-stick properties, and electrical insulation. They can resist the corrosion of almost all chemical agents, including hydrofluoric acid, concentrated sulfuric acid, and aqua regia. By utilizing the principle of plastic processing of fluoroplastics, these materials are used as a lining inside ordinary steel housings to prevent direct contact between the steel and highly corrosive substances. This approach addresses both the issue of low strength and inability to withstand high pressures in fluoroplastics, as well as the problem of steel’s poor corrosion resistance. Fluoroplastic-lined butterfly valves exhibit excellent heat and cold resistance, as well as good electrical insulation and superior chemical stability. They can withstand the corrosion of various strong acids, strong bases, and strong oxidizing agents. They feature very low friction and self-lubricating properties, allowing them to be used over a long period in temperatures ranging from -195 to 200°C. I. Structure and Application Scope of Fluorine-Lined Butterfly Valves 1. Structure and names of main components: (1) Driving mechanism; (2) Dust-proof seal ring; (3) O-ring; (4) Butterfly disc; (5) Lining layer of the butterfly disc; (6) Lining layer of the valve seat; (7) Valve body 2. Application scope: The nominal pressure of fluoroplastic-lined butterfly valves is PN116 (the maximum pressure that fluoroplastic can withstand is 215 MPa). DN50～1 200. The suitable operating temperature for valves is determined based on a comprehensive assessment of the temperatures that the various materials used (metallic and non-metallic materials) can withstand. Materials such as steel-lined fluoroplastic (WCB + F46) can be used at temperatures ranging from -29 to 150°C. The maximum value is limited to no more than 150°C. The applicable media include corrosive substances such as low-viscosity acids and bases, referring mainly to highly corrosive substances like acidic, alkaline, organic, and inorganic solvents. Low viscosity refers to media with a relatively high concentration of particles; valves lined with fluoroplastic materials should try to avoid being used with media that contain solid particles. II. Testing Methods for Fluorinated Butterfly Valves 1. Temperature: The measurement of test temperatures covers a range from room temperature to liquid nitrogen temperature; thermocouples are used for this purpose. The temperatures are measured, recorded, and input into a control computer using a digital multimeter, where they are displayed on the computer screen. The computer then automatically handles the recording and storage of these values. At the same time, the computer sends the temperature measurement values to the temperature display on the instrument panel for on-site display. 2. Pressure: The measurement range for the test pressure is 0～10 M Pa. Pointer-type precision pressure gauges and digital pressure gauges are used to display the system pressure on the instrument panel in real time. At the same time, pressure transmitters are employed to measure the system pressure and convert it into voltage signals, which are then measured and collected by a digital multimeter before being fed into a measurement and control computer. The data is displayed on the computer interface, and the computer automatically handles the recording and storage of this information. 3. Liquid level: To ensure that the liquid nitrogen level meets the requirements for butterfly valve testing, a differential pressure transducer is used to measure the liquid level. The electrical signal is measured using a digital multimeter, collected, and input into a computer for display; it also alerts the user to add liquid nitrogen and to stop the liquid nitrogen addition process. 4. Flow rate: Depending on the sealing type of the butterfly valve, the allowable leakage amount of the valve varies. Fluorine-lined butterfly valves with a soft-sealing structure should have zero leakage. As for fluorine-lined butterfly valves with a hard seal, a certain amount of leakage is permitted. Based on the above considerations, two types of devices for measuring flow rate are employed: one is a flow meter for low flow rates, used to measure the leakage from hard-sealed or soft-sealed valves that are permitted to have a certain level of leakage under relatively abnormal operating conditions. For minor leakage amounts, which cannot be detected by ordinary flow meters, measurement is carried out by observing and counting the number of bubbles leaking from the open end into the water. A computer data acquisition system is used to record the number of electrical pulses, enabling automatic counting. Main lining materials for fluorinated valves: Polyperfluoroethylene FEP (F46) is suitable for use with any organic solvents or reagents, as well as dilute or concentrated inorganic acids, bases, alkanes, aromatics, chlorinated hydrocarbons, etc. 　 Operating temperature: -85~150 Features: Its mechanical, electrical properties and chemical stability are essentially the same as those of F4, but its key advantage is high dynamic impact toughness, along with excellent weathering and radiation resistance. 　 Polytrifluoroethylene PCTEF (F3) Applicable media: Various organic solvents, inorganic corrosive liquids (oxidizing acids) Operating temperature: -195~120 Features: Its heat resistance, electrical properties, and chemical stability are second only to those of F4; its mechanical strength, creep resistance, and hardness are better than those of F4. 　 Polypropylene: RPP. Applicable media: aqueous solutions of inorganic salts, inorganic acids, and dilute or concentrated solutions of alkalis. 　 Operating temperature: -14~80 Features: One of the lightest plastics; it boasts higher yield, tensile, and compressive strengths as well as greater hardness than low-pressure polyethylene. It exhibits excellent rigidity, good heat resistance, is easy to mold, and is cost-effective. Modified dynamic impact resistance, fluidity, and bending elasticity. 　 Polyvinyl chloride: Rigid PVC. Suitable media: water, concentrated alkalis, non-oxidizing acids, alkanes, oils, and ozone. 　 Operating temperature: 0-55 Features: High mechanical strength, excellent chemical stability and dielectric properties, good oil resistance and aging resistance, easy to weld and bond, and low cost. 　 Polytetrafluoroethylene PTFE (F4) Application media: strong acids, strong bases, strong oxidizing agents, etc. 　 Operating temperature: -200~180. Features: It possesses excellent chemical stability, high heat and cold resistance, a very low friction coefficient, making it an excellent self-lubricating material. However, its mechanical properties are poor, its fluidity is low, and it experiences significant thermal expansion. 　 Polyvinylidene chloride PVDF(F2): Medium used: Resistant to most chemicals and solvents; Operating temperature: -70~100. Features: Better tensile strength to compressive strength ratio than F4, resistant to bending, weathering, and radiation. It is resistant to light and aging, etc.; its main advantages are good toughness and easy formability. Polyolefins: PO Applicable media: acids, bases, salts at various concentrations, and certain organic solvents. 　 Operating temperature: -58~80. This article is reprinted from the official website of Zhejiang Xiangsong Valve Co., Ltd. Please continue to add explanations for any incorrect or incomplete parts, so that those who read it next will learn more. 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