I would like to ask about the penetration of chloride ions into tetrafluoride
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This post was last edited by 25_mbzcc on 2024-10-23 at 22:56. Hello, all the experienced professionals in the chemical industry. I’m new to the chemical industry, and recently I was given a task – or rather, a problem to solve – related to an issue that has persisted for some time in our department. There is a set of tower equipment in the plant, and more than 76% of the fluid flowing through the pipes is sulfuric acid with trace amounts of chlorine. An electromagnetic flowmeter (with tantalum electrodes and a PTFE lining) is used to measure the flow rate; there is a heat exchanger before the flowmeter, ensuring that the temperature of the fluid remains below 50°C. Over time, the flow meter reading keeps dropping, but the actual flow rate remains within the normal range. At first, it was thought to be electrode corrosion or lining corrosion. Experienced professionals in the industry said that chloride ions penetrating into the structure caused a decrease in the insulation properties of the lining, and that there is no effective solution at present; therefore, I turned to the internet for advice, hoping that those with more experience online could share any strategies they have for dealing with this issue. Also, after searching online for a long time, I couldn’t find any information on chloride ion penetration through PTFE linings; so I’m daring to ask the experts if they could provide me with some information on this topic{:1_90:}
In this case, it is likely that chloride ions have affected the tetrafluoro lining. Although PTFE has strong corrosion resistance, in an environment with high concentrations of sulfuric acid and trace amounts of chlorine, chloride ions can still penetrate into the PTFE material. This penetration may cause changes in the microstructure of the tetrafluoro lining, thereby affecting the measurement accuracy of the flow meter. It is recommended to regularly check the integrity of the PTFE lining, and consider using more impermeable materials or adding a protective layer. At the same time, monitor the chlorine concentration to ensure it remains within safe limits, thereby reducing potential damage to the equipment. .
Thank you for the reply! I would like to build on this discussion by adding a few details and raising some questions: 1. I’m very curious about what the responder meant by “materials with better resistance to penetration or additional protective layers” – could you give some examples? 2. According to the experienced workers, the infiltrated lining appears normal in appearance (its integrity is preserved). What testing methods can be used to determine that it was caused by chloride ion infiltration? Using a resistance meter to test is a feasible method. 3. The electromagnetic flowmeter, which was replaced just last November, showed almost zero readings by October this year; its rate of failure is astonishing. What is the typical service life of electromagnetic flowmeters used in hydrochloric acid or other media containing chloride ions? 4. Due to production requirements, the flow meter cannot be repaired during operation; it can only be removed and replaced during major overhauls. May I ask the experienced colleagues at Haichuan how they maintain the flow meters during operation?
I. Optimize equipment material selection: Improve the lining materials – for PTFE linings, it is possible to use higher-grade corrosion-resistant fluoroplastic materials or new types of composite material linings. These materials may have better density and impermeability, reducing the penetration of chloride ions. For example, some new types of fluoropolymer linings can better prevent the penetration of chloride ions while maintaining their resistance to sulfuric acid. II. Enhance protective measures 1. Coating protection: Apply a special protective coating to the inner surface of the flow meter. Such a coating should possess excellent resistance to sulfuric acid and chloride ions, enabling it to form an effective barrier that prevents the penetration of chloride ions. For example, nano-ceramic coatings or polymer coatings can be used; these coatings can be applied to the inner lining of flow meters through methods such as spraying or impregnation. 2. Install a diaphragm: A corrosion-resistant diaphragm is installed in the measuring section of the flow meter to separate the electrodes from the medium. The diaphragm should be made of a material that has high tolerance to sulfuric acid and chlorine, and that can effectively prevent the penetration of chloride ions. This reduces the chance of direct contact between the electrode and the lining with the medium, thereby lowering the risk of corrosion and penetration. III. Improvement of the process flow: Dechlorination treatment: A dechlorination device is added before the medium enters the flow meter to reduce the chloride ion content in the medium. Chloride ions can be removed using methods such as chemical adsorption and ion exchange. For example, special adsorbents or ion exchange resins can be used to adsorb or exchange out chloride ions from the medium, thereby reducing their impact on the flow meter.
There are many processes for steel-lined PTFE; to increase the density of PTFE, the isometric pressing process is available at present, and you might want to give it a try