The design of the material selection tests should simulate the actual operating conditions of the equipment as closely as possible; otherwise, the results will vary

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An industrial organic synthesis experiment was carried out in a pilot plant; the excess acid was partially neutralized with ammonia, the slurry was filtered, and the ammonium bisulfate filtrate was sent to a second unit where it was ultimately converted into ammonium sulfate. Past experience and tests on (equipment components of ammonium sulfate plants) show that 316 stainless steel is highly corrosion-resistant for the entire process. However, two-stage tests were conducted for safety: from acid to bisulfate, and from bisulfate to sulfate. Tests conducted by preparing solutions using laboratory chemicals showed that 316 stainless steel possesses excellent corrosion resistance. However, actual pilot-scale solutions yield different results; even slightly heated solutions (around 35°C) cause rapid corrosion of the stainless steel surface, leading to a degradation of the metal structure. The reason is that the partially neutralized acid contains about 1% of partially decomposed residual organic matter, which severely damages the passivation film of stainless steel in less than 4 hours. This example once again shows that the design of material selection tests should simulate the actual operating conditions of the equipment as closely as possible; therefore, the environmental conditions must be determined in advance, especially with regard to any minor impurities present in the environment. Of course, the issue can also be considered from another perspective. If the partially neutralized solution is oxidized to remove the residual organic matter, then it is completely acceptable to use 316 stainless steel.