Classification, Standards, and Installation Requirements for Manholes on Pressure Vessels

I. Overview of Manholes

A manhole is a safety accessory installed on the side wall or top of equipment such as pressure vessels, storage tanks, and reactors. It allows personnel to enter the equipment for inspection, cleaning, and maintenance, and can also serve as a ventilation or observation port. The design and installation of manholes directly affect the safe operation and maintenance convenience of the equipment.

II. Classification of Manholes

1. Classification by pressure rating:

Atmospheric manhole: Suitable for atmospheric or slightly positive pressure vessels;

Pressure vessel manhole: Suitable for containers that withstand a certain internal pressure, classified by nominal pressure into PN0.6, PN1.0, PN1.6, PN2.5, PN4.0, etc.

2. Classification by structural form:

Swing cover manhole: The cover is opened by rotating around a pin, making it easy to operate and the most commonly used type;

Vertical hinged manhole: The cover is lifted vertically to open, suitable for the top of equipment;

Horizontal-lift manhole: The cover is lifted horizontally to open, suitable for the side walls of equipment;

Quick-opening manhole: Equipped with a quick-locking mechanism for rapid opening, suitable for applications requiring frequent access;

Manhole with core: Equipped with an internal anti-vortex baffle, suitable for storage tanks.

3. Classification by installation position: Side manhole, top manhole.

III. Execution Standards

Domestic standards: The HG/T 21514~21535 "Steel Manholes and Handholes" series of standards, covering manholes of various types, pressure ratings, and materials; JB/T 577 "Manholes for Pressure Vessels".

International standards: ANSI/ASME B16.5 (flange connection part), DIN 28011~28014 "Manholes for Pressure Vessels".

IV. Common Materials

Shell/Flange: Q235, 20#, Q345R, 304, 304L, 316, 316L;

Gaskets: asbestos rubber gaskets, flexible graphite gaskets, metal wound gaskets, PTFE gaskets;

Fasteners: Grade 8.8 and Grade 10.9 bolts, made of materials such as 35CrMo and 25Cr2MoV.

V. Installation Requirements

1. The manhole installation location should facilitate personnel entry, exit, and operation, with sufficient space around it;

2. The center of the side wall manhole is generally 750 to 1500 mm above the ground or operating platform;

3. The top manhole shall be located at a position on the top of the equipment that is easy to climb, and shall be equipped with a ladder and a platform;

4. The sealing surface of the manhole flange shall be flat and free of radial scratches;

5. Bolts shall be tightened symmetrically and evenly, with the tightening torque meeting the requirements of the specifications;

6. After installation, a hydrostatic test and an airtightness test shall be conducted to confirm that there are no leaks;

7. The manhole should be closed promptly after being opened. It is strictly prohibited to leave it open for an extended period.

VI. Safety Precautions

1. Before entering the equipment, purging, ventilation, and testing must be performed, and entry is permitted only after safety has been confirmed;

2. A confined space work permit must be obtained before entering the equipment, and a dedicated person must be assigned to monitor the work;

3. The manhole cover should be opened slowly to prevent injury from internal pressure;

4. After maintenance is completed, the manhole should be promptly restored to ensure a reliable seal.

Cangzhou Kairuifeng Pipeline Equipment Co., Ltd. specializes in the production of manholes for various pressure vessels, offering a full range of specifications and customization options. We welcome your inquiries and purchases.