Do the manholes on the tank roof need to be tightened with bolts?
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It is said that the manhole on the top of the tank also serves to release pressure from inside the tank when the breathing valve fails – is that correct? If that’s the case, then it shouldn’t be tightened with bolts, right?
I’m not quite sure; I’ve seen many large containers that are open
It might be related to the substances stored inside
It’s not necessary, but it also can’t be left uncovered. If there are volatile substances in the container, it should be tightened as much as possible.
The manhole flange on the top of the tank should be tightened, as 1. it prevents rainwater from entering the tank； 2. Prevent people from tripping and falling into the tank ； 3. Reduce the evaporation of materials
Typically, storage tanks equipped with breather valves are pressurized with nitrogen to prevent the oxidation of the products inside the tank. Set the pressure at around -50 to 300 KPA. Manholes must be sealed. Otherwise, it will get polluted.
The design pressure for standard dome tanks is generally -500 to 2000 Pa, while storage tanks with elliptical heads are not subject to this limitation. Whether to open the manhole on the top of the tank depends mainly on whether the medium inside the tank is allowed to come into contact with air.
It is said that the manhole on the top of the tank also serves to release pressure from inside the tank when the breathing valve fails, but I think this claim is incorrect. The function of a breather valve is to release pressure outward when the pressure inside the tank is high, and to supply pressure to the tank when the pressure is low, thereby maintaining pressure balance. As a manhole on the top of the tank, it is generally opened during tank cleaning to allow personnel to enter. I believe that the manhole on top of the tank should be sealed tightly for the following reasons: 1. When the tank contains volatile substances, it is necessary to ensure proper sealing; otherwise, in the event of a leak, accidents and environmental pollution can occur ； 2. Tightening the manhole on the top of the tank ensures good sealing performance, preventing other impurities from entering and thus maintaining the purity of the medium inside the tank ； The above are my personal opinions.
Suppose there is a situation where, when material is fed into the tank, the breather valve fails and is unable to release the oil vapor; in that case, the pressure inside the tank will gradually increase. When it reaches a certain level, the pressure will force the manhole open (without having to tighten any bolts), thereby achieving pressure relief. If the pressure continues to rise after the manhole is bolted shut, it may exceed the tank’s design pressure.
Whether the lid of the tank top manhole is properly secured should mainly depend on the medium inside the tank and the environmental requirements for that medium (i.e., pressure); in my opinion, the bolts should be tightened.
It should be this: emergency pressure relief manhole. Here is the introduction: http://bbs.hcbbs.com/viewthread.php?tid=419182