When selecting corrosion-resistant materials, the coupon testing and methods must be correct and appropriate; otherwise, they have no practical value as a reference
Thread Content
Previously, the hydrogen chloride gas scrubbers and mist eliminators in a certain plant were made of reinforced phenolic plastic, and they could only be used for 2 to 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. The failure of the material screening test in this experiment was due to the incorrect placement of the samples; they were exposed to the gas phase rather than to the washing solution, resulting in a significant difference between the test environment conditions and the actual environmental conditions. Conducting coupon tests inside production equipment has a great advantage for evaluating the corrosion resistance of materials under the environmental conditions present in that equipment, namely the authenticity of those environmental conditions. Whether a realistic environment 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 pieces. The sampling location should be representative and able to reflect the main characteristics of the corrosion conditions of the equipment.
When selecting corrosion-resistant materials, the design and execution of coupon tests are crucial. As you mentioned, when a certain factory selected materials for washers and demisters, improper placement of the test specimens resulted in test results that did not accurately reflect the corrosion resistance of those materials under actual operating conditions. The failure of the coupon test reminds us that the test design must ensure that the coupon location represents the actual corrosion environment within the equipment. The correct location for placing the test specimens should be: 1. **Environmental representativeness**: The placement location must be in the part of the equipment most susceptible to corrosion, or in an area where the type and severity of corrosion are representative of the entire equipment. 2. **Contact medium**: Ensure that the test pieces can come into contact with all relevant media present during equipment operation; in your case, the test pieces should be placed in the washing solution rather than being exposed only to the gas phase. When conducting coupon testing, the following factors should also be considered: - **Testing duration**: Select an appropriate testing period to ensure that any corrosion that may occur in the material over time can be observed. - **Monitoring and data recording of the tests**: Regularly inspect the corrosion status of the test pieces and record the degree of corrosion in detail; these data will help assess the actual corrosion resistance of the material. Through these measures, the corrosion resistance of materials under actual operating conditions can be assessed more accurately, thereby providing a scientific basis for the selection of corrosion-resistant materials. .