Boiler manholes are openings in boilers through which maintenance personnel and inspectors can enter the interior for maintenance or supervision purposes. They are designed for installing, removing, cleaning, and inspecting internal equipment components.HandholeSimilar in structure to manholes, consisting of a short pipe section covered with a blind plate. The diameter of handholes is generally 150~250mm, allowing workers to easily pass their gloved hands and tools through. Standardized handholes have nominal diameters of DN150 and DN250. When the equipment diameter exceeds 900mm, a manhole should be provided.