Inadequate process operation and maintenance can also lead to corrosion accidents

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We know that the material selection, design, manufacturing, and installation of equipment have a significant impact on its corrosion resistance. However, the operation and maintenance of the equipment also play a very important role. Whether the process parameters are appropriate, the operation is stable, and the maintenance is proper all affect the corrosion resistance and service life of the equipment. If the environmental conditions exceed the corrosion resistance limits of the equipment materials, corrosion incidents are inevitable. Example: A tower of a certain company was equipped with titanium internals. During the shutdown, the operators took it upon themselves to clean it with hot concentrated hydrochloric acid. As a result, the titanium components were severely corroded and almost completely dissolved. Analysis: This is a typical example of equipment suffering corrosion damage due to a lack of basic knowledge about corrosion. Also, for example, if a factory’s hydrochloric acid storage tanks are made of stainless steel, some workers use stainless steel buckets to transport the hydrochloric acid, and so on. The mistake here is assuming that titanium and stainless steel are excellent corrosion-resistant metal materials, and therefore will not corrode in any medium. We know that the corrosion behavior of metals is closely related to environmental conditions; therefore, it is impossible to discuss the corrosion resistance of metals without taking these environmental conditions into account. For a metal, not only the type of medium but also factors such as its concentration, temperature, gas presence, impurities present, and flow velocity can have a significant impact on the pattern and rate of corrosion of the metal. Only when the hydrochloric acid concentration is below 10% and the temperature is below 40°C is there a lower corrosion rate. That is, titanium can only be used in dilute hydrochloric acid at room temperature. At higher temperatures, the hydrochloric acid concentration must be lower. The corrosion rate of titanium in hot concentrated hydrochloric acid is very high. At 60°C in 20% hydrochloric acid, the erosion rate of titanium reaches 20 mm/y. Similarly, ordinary stainless steel is also resistant to hydrochloric acid corrosion. Because, like titanium, the corrosion resistance of stainless steel depends primarily on an oxidizing environment, whereas hydrochloric acid is a non-oxidizing acid. For example, Cr18Ni9 stainless steel has a corrosion rate of around 10 mm/year in 5% hydrochloric acid at room temperature, which is similar to that of carbon steel.