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Requirements for selecting corrosion allowance: 1. Except as specified in Article 6 below, corrosion allowance shall be considered for the cylinder, head, nozzles, manholes, and internal components that come into contact with the working medium. 2. When there are specific provisions regarding the corrosion margin for containers in the process system engineering field or in engineering design documents, or when there is existing practical experience in this regard, the corrosion margin should be determined in accordance with those specific provisions or experience. 3. For containers suffering from uniform corrosion, when reliable data are available, the corrosion margin should be calculated using the following formula: C2 = Design service life x Corrosion rate. 4. During design, consideration must also be given to the effects of the medium on the erosion, wear, and local corrosion of the container’s shell or components. 5. For components in contact with the medium on both sides, different corrosion margins should be selected based on the respective operating media on those two sides; the sum of these two margins shall serve as the total corrosion margin for the component. 6. Corrosion allowance may not be considered in the following cases: 1) When the medium has no corrosive effect on stainless steel (components made of stainless steel, stainless steel composite plates, or stainless steel surfacing layers); 2) For base materials equipped with reliable corrosion-resistant linings (such as lead lining, rubber lining, plastic lining, etc.); 3) The sealing surfaces of flanges; 4) The heat exchange tubes, gussets, floating head bolts, longitudinal partitions, tie rods, spacing tubes, baffle plates, and support plates of shell-and-tube heat exchangers; 5) The outer surface of containers and their external components that can be effectively protected against environmental corrosion by painting (such as supports, legs, brackets, tower top hangers, etc., but not including skirt bases and foot bolts); 6) Removable tray plates, packing, etc. Unless otherwise specified in the technical documents related to the process system or in the engineering design documents, the corrosion margin of containers shall be determined in accordance with the following provisions. 1. The corrosion margin of the container shell and head shall comply with the following provisions: 1) For containers made of carbon steel or low-alloy steel that are used with compressed air, steam, or water as the medium, the corrosion margin shall not be less than 1.0 mm; 2) In all other cases except those specified in item 1) of this paragraph, the corrosion margin of the container may be taken according to the values specified in the table below; 3) If the corrosion margin exceeds 6 mm, more corrosion-resistant materials such as composite steel plates, surfacing layers, or linings shall be used; 4) The corrosion rate can be determined based on engineering design practices or by referring to relevant corrosion manuals