Detailed Analysis Of The Manhole

1.Definition and function
Manhole is an open structure on equipment or containers for personnel access, maintenance, cleaning or inspection, commonly found in storage tanks, boilers, reactors, underground pipelines, ship cabins and other confined Spaces. Its core functions include:

● Safe passage: Provides access to restricted Spaces.
● Maintenance and inspection: easy to clean, repair or test inside the equipment.
● Emergency escape: part of the design takes into account the emergency exit function.

2. Structure composition

The manhole usually consists of the following components:

● Manhole Cover: Cover plate that closes the opening and meets sealing and pressure requirements.
● Flange or Frame: Welded or bolted to the container to support the manhole cover.
● Gasket: to ensure the air tightness or liquid tightness between the cover plate and the flange.
● Locking device: bolt, hinge, quick-opening mechanism, etc., used to fix the cover plate.
● Reinforcement Ring: prevents stress concentration at the opening of the container.

3. Main types
Sort by installation location
● Vertical manhole: Vertically installed on the top or side of the device.
● Horizontal manhole: horizontally mounted on the side of a container, commonly found in storage tanks or long pipes.
● Embedded manhole: Flush with the surface of the device to reduce space consumption.

Classified by function and design
● Normal pressure manhole: for non-pressure or low pressure vessels (such as storage tanks, sewage Wells).
● Pressure manhole: pressure resistant design, suitable for boilers, reactors and other pressure equipment (such as HG/T 21514 standard).
● Quick opening manhole: Equipped with hinge, pneumatic or hydraulic opening and closing device for frequent operation.
● Explosion-proof manhole: equipped with explosion-proof disc or flame arrester for flammable and explosive environment.
● Sanitary manhole: surface polishing, no dead Angle, used in food, pharmaceutical industry.

4. Material selection

● Carbon Steel (Q235, 20R) : universal, low cost, need anti-corrosion coating.
● Stainless steel (304, 316L) : corrosion resistance, suitable for chemical and food industries.
● Aluminum alloy: Lightweight, used in ships or mobile equipment.
● Composite material (glass fiber reinforced plastic, PP) : acid and alkali corrosion resistance, used in sewage treatment.
● Special alloys (titanium, Hastelloy) : extreme high temperature or corrosive media.

5. International standards and norms

● Chinese standard:
Pressure vessel: HG/T 21514~21535 (series standard, such as rotary cap, vertical hanging cap manhole).
Atmospheric vessel: JB/T 5779 (tank manhole).
● American standard: ASME VIII (pressure vessel), ANSI/AWWA C110 (water supply and drainage).
● European standard: EN 1092-1 (flange connection), EN 12516 (pressure equipment).
Other: ISO 14122 (Safety Specification for Industrial Equipment Channels).