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　 　Pressure-resistant manhole For finished products, the typical diameter is 600 mm, with the center positioned approximately 750 mm above the floor. This height facilitates access for personnel during tank cleaning and maintenance. Manholes on non-metallic tanks are located at the top of the tank, while those on metallic tanks are mounted on the bottom ring plate. Most are circular openings with a diameter of 600 mm, with their centers situated 750 mm from the bottom plate. These openings serve as entry points for personnel conducting tank cleaning or maintenance and are also referred to as doors.

　　During maintenance and cleaning of the tank, manholes may be used for lighting and ventilation. For vertical tanks with a capacity of 5,000 m³ or less, one to two separate manholes are required; for capacities exceeding 5,000 m³, two separate manholes are required. The manholes shall be positioned at an angle of at least 90° relative to the tank’s oil piping. When only one manhole is provided, it shall be located opposite the tank roof light opening; when two manholes are installed, one shall face the transparent opening, and the other shall be spaced at an angle of no less than 90° from the first.

　　A manhole shall be provided on the right side of the enclosure’s oil pipe, positioned as close to the compartment as possible to facilitate access for personnel, maintenance, and ventilation. Given that pressure‑rated manholes are installed at the lower perimeter of the enclosure, preventing leaks is of paramount importance. The mating surfaces of the two flanges must be perfectly flat, with no warping or torsional distortion. Reinforcing ribs and flanges should be cut from a single sheet of steel whenever feasible; they must not be joined by welding. Both the flanges and the cover plate are equipped with sealing rings, which require careful protection during installation. Sealing shall be achieved using 3 mm‑thick asbestos‑rubber gaskets, which must remain intact and free from cracking. When tightening the bolts on the enclosure’s flanged cover, apply even torque in a diagonal sequence to prevent deformation of the cover.

　 　Pressure-resistant manhole It refers to an opening structure provided for personnel to perform enclosure‑related work, maintenance, and safety inspections. It typically consists of a short cylinder, a flange, and a manhole cover with a handle. For safety inspections, the number and dimensions of the flanges required for pressure vessels are specified in the “Inspection Port” section. Flanges are available in carbon steel or stainless steel. Based on operating pressure, manholes are classified as atmospheric‑pressure manholes and pressurized manholes. Manhole covers may be equipped with either a hinged lid or a suspended lid; flange‑opening mechanisms come in standard and quick‑release versions. The design and dimensions of flanges have been widely standardized.

　 　Pressure-resistant manhole When procuring, pay close attention to the calculation of flange reinforcement; otherwise, tank maintenance could endanger the safety of maintenance personnel. The access areas of core‑equipped manholes can be classified as straight flanges, tee flanges, cross flanges, and angled flanges. Flanges are available in five angles: 15°, 30°, 45°, 60°, and 75°. Each flange angle can be adjusted within a tolerance of ±7.5°.

　　The top‑mounted pressure‑resistant manhole with a safety emergency ventilation system is typically equipped with a flame arrester and utilizes a mechanical breather valve. This design helps prevent damage and accidents caused by rapid overpressure or vacuum, while also providing fire‑safety protection, making it an essential safeguard. It is particularly well suited for atmospheric‑type roof‑covered tanks storing nitrogen gas. The device offers advantages such as constant‑pressure discharge, constant‑pressure intake, flexible opening and closing, enhanced fire safety, a compact structure, excellent sealing performance, and reliable operation.