GB/T 20644.1-2025 "Guide for Selection in Special Environmental Conditions - Part 1: Protective Coatings for Metal Surfaces" is applicable to the selection of organic coatings, metallic coatings, and inorganic coatings for metal surfaces. It replaces the 2006 edition and expands the types of environments covered. The standard addresses six categories of special environments: dry heat, dry desert, plateau, humid marine, humid, and cold, specifying the differentiated requirements for protective coatings in each environment. It stipulates the classification system for protective coatings, selection principles, evaluation items, and test methods, including natural atmospheric exposure and artificial simulation tests (such as salt spray and light aging tests). The standard provides recommended coating schemes for different substrate materials, offering unified guidance for the protective design, material selection, and effectiveness verification of metal components in special environments, thereby ensuring their service reliability.