Wastewater electromagnetic flowmeter electrode corrosion resistance to the measurement medium is the choice of material considerations, followed by consideration of whether the surface effects such as passivation and the noise formed.
1. Select corrosion-resistant materials. The corrosion resistance of electrodes is very high. Common metal materials include molybdenum-containing acid-resistant steel 1Cr18Ni12Mo2Ti, Hastelloy (corrosion-resistant nickel-based alloy) B, C, titanium, tantalum, platinum-iridium alloy, which can cover almost all chemical liquids. In addition, there are low-noise electrodes suitable for slurries, etc. They are conductive rubber electrodes, conductive fluoroplastic electrodes and porous ceramic electrodes, or metal electrodes coated with these materials. In principle, the choice of electrode materials should be determined by the user's actual application of the medium in other equipment or past experience.
2. Avoid electrode surface effect. The corrosion resistance of the electrode is an important factor in selecting materials. However, sometimes the electrode material has good corrosion resistance to the measured medium, but it is not necessarily a suitable material. It is also necessary to avoid the electrode surface effect. The electrode surface effect is divided into three aspects: surface chemical reaction, electrochemical and polarization phenomenon, and electrode catalytic effect. Chemical reaction effects, such as the formation of a passivation film or oxide layer after the electrode surface contacts the measured medium. They may play a positive protective role in corrosion resistance, but they may also increase the surface contact resistance.
For example, tantalum will be oxidized when in contact with water, forming an insulating layer. For medium-electrode material matching to avoid or reduce the electrode surface effect, there is not enough information available as for corrosion, only some limited experience, which needs to be accumulated in practice. The grounding ring is connected to both ends of the flow sensor of the plastic pipe or the metal pipe with insulating lining. Their corrosion resistance requirements are lower than those of the electrode, and acid-resistant steel or Hastelloy is usually selected. Due to their large size, precious metals such as tantalum and platinum are rarely used for economic reasons. If the metal process pipeline is in direct contact with the fluid, no grounding ring is required.
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