In material selection tests, the location of the test specimens must be chosen carefully so as to accurately reflect the main characteristics of the corrosion conditions experienced by the equipment.

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Example: The hydrogen chloride gas scrubbers and mist eliminators in a certain company were originally made of reinforced phenolic plastic, and could only last for 2–3 years. To select more corrosion-resistant materials, coupon testing was conducted in washers and demisters, showing that Hastelloy C-276 (with a composition of 00Cr16Ni57Mo16Fe6W4) can be used for washers, while alloy 20 (chromium-nickel stainless steel) can be used for demisters. However, the equipment made from these high-grade corrosion-resistant alloys was corroded and damaged within two weeks and four weeks respectively. Problem analysis: It is reported that the actual corrosion behavior of the material differs significantly from the results of the coupon test due to the incorrect placement of the coupons; they were not exposed to the washing solution but rather to the gas phase. As a result, the experimental environmental conditions differ greatly from the actual environmental conditions. Suggestion: Conduct coupon testing inside the production equipment, as this offers a significant advantage for evaluating the corrosion resistance of materials under the environmental conditions present in that equipment, namely the authenticity of those environmental conditions. Whether true environmental conditions can be achieved depends on the design of the experiment, with the most important factor being the correct selection of the location for the test specimens. The test piece location should be representative, capable of reflecting the main characteristics of the corrosion conditions of that equipment.