Should a nitrogen-sealed tank be equipped with an emergency breathing manhole or an emergency pressure relief manhole?
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Large storage tanks are equipped with nitrogen seals and vent valves; some design firms include emergency venting manholes, which provide protection against both overpressure and underpressure conditions, while others provide emergency pressure relief manholes that only protect against overpressure. What is the proper way to design them in order to ensure compliance and Reasonableness?
According to relevant regulations, nitrogen-sealed tanks should be equipped with emergency pressure relief manholes. Since nitrogen is an inert gas that does not easily cause combustion or explosion, when overpressure occurs inside a nitrogen-sealed tank, the pressure must be released through pressure relief manholes to ensure the safety of the tank. Emergency breathing manholes can improve ventilation of the wound, but they cannot directly relieve the overpressure caused by nitrogen; therefore, they are not very suitable for the safety design of nitrogen-sealed tanks. .
Emergency breathing manholes can prevent the storage tank from deflating
API 2000 makes it clear that all of these are required: nitrogen sealing, breathing function, emergency pressure relief, and weak top connections
For the safe design of large storage tanks, it is very important to have controls to prevent overpressure under positive pressure as well as under negative pressure. To ensure the safety of storage tanks, designers should employ safety devices such as nitrogen sealing, breather valves, safety valves, and manholes installed according to the tank’s volume. Regarding the issue you mentioned, sealed containers include storage tanks and oxygen containers, etc. Normally, installing a nitrogen seal can reduce the oxygen level and the risk of material oxidation, thereby enhancing safety. As for the emergency breathing manholes and emergency pressure relief manholes, their main purpose is to prevent rapid changes in atmospheric pressure, thereby avoiding damage to storage tanks, containers, and their safety valves. When selecting orifices, an analysis based on specific circumstances is necessary; different safety protection devices should be designed to address various levels of risk and situations, so as to effectively counteract various risk events in a compliant and appropriate manner. At the same time, throughout the safety design, it is necessary to carry out regular monitoring and control of the gases and chemicals present in the storage tanks, in order to prevent residues and chemical hazards from affecting human health or the environment.