Structure
Manholes have been shaped products, usually 600mm in diameter. The center of the manhole is generally 750mm from the floor. It is convenient for the staff to enter and exit the oil tank or ventilate during installation, cleaning and maintenance.
The manhole of the non-metal oil tank is set on the top of the tank, and the manhole of the metal oil tank is set on the bottom plate of the tank wall. Most of them are round holes with a diameter of 600mm, with a center distance of 750mm from the bottom plate. They are used for tank cleaning or maintenance personnel to enter and exit the tank. They are also called gates. Use manholes for lighting and ventilation at all times during maintenance and cleaning of oil tanks. Vertical oil tanks have 1 to 2 manholes when the capacity is below 5000m3, and 2 manholes for those above 5000m3. The installation of the manhole should be no more than 90° away from the oil inlet and outlet pipelines. When only one manhole is provided, it should be placed on the opposite side of the light-transmitting hole on the top of the tank; when two manholes are provided, one of them is located on the opposite side of the light-transmitting hole, and the other should be separated from the first manhole by at least 90 °.
One manhole should be located near the right side of the oil inlet and outlet pipes, and try to make the manhole face the closed door of the tank chamber so as to facilitate the entry and exit of the oil tank and the ventilation pipe.
Since the manhole is installed on the bottom ring of the oil tank, leakage prevention is particularly important. It is required that the joint surface of the two flanges must be flat and free of twisting. Reinforcing plates and flanges should be cut on the whole steel plate without splicing. The flange and cover plate are processed with sealing rings, so special attention should be paid to protection during construction. 3mm thick asbestos rubber gasket is used for sealing, no cracks are allowed. When installing the manhole cover to tighten the bolts, force evenly at diagonal angles to prevent deformation of the manhole cover.
Installation and maintenance
Because the manhole is located in the lower part of the oil tank, the manhole is subject to great liquid pressure. In order to prevent leakage, the installation quality of the manhole must be strictly required. The flanges and cover plates are processed with sealing water lines, which should be protected during construction to avoid oil leakage during use. Make a mark every time the manhole is removed to avoid dislocation during reinstallation and affect tightness. When installing the nuts on the manhole cover, apply force evenly in pairs to prevent oil leakage caused by deformation of the cover or uneven force.
