Is it necessary to install a negative pressure suction system for the accident relief equipment?
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SH/T3007: Storage tanks that use nitrogen or other inert gases as sealing agents shall be equipped with emergency pressure relief devices, and shall comply with the following requirements: a) The operating pressure of the emergency pressure relief device shall be higher than the venting pressure of the breather valve and shall be less than or equal to the design pressure of the storage tank； b) The accident relief equipment shall meet the ventilation requirements to ensure the safety of the storage tank in case of failures in the nitrogen sealing or other inert gas sealing pipeline systems, or in the breather valves ； c) The accident relief equipment can be directly connected to the atmosphere ； d) For accident pressure relief, emergency vent manhole covers or breathing manholes with a diameter of not less than DN500 should be selected ； The regulatory provisions do not indicate that the accident relief equipment must have the function of drawing in air under negative pressure ； In Sinopec’s Document No. [2016] 127 – \"Guidelines on the Implementation Plan for VOCs Control Projects in Petrochemical Storage and Transportation Tank Areas, as well as Safety Measures\" – the example diagrams showing the set pressure values for atmospheric pressure tanks do not indicate the negative pressure vacuum-breaking function of emergency relief valves; this function is instead handled by breather valves ； I would like to ask everyone: when designing a pressure vessel at atmospheric pressure with nitrogen sealing in place, how is the negative-pressure vacuum-breaking function of the emergency relief valve taken into account?
According to the regulatory provisions and the description in Sinopec’s Letter on Refining and Production [2016] No. 127, accident relief equipment does not require a negative pressure suction function. When nitrogen or other inert gases are used to seal and protect systems in atmospheric-pressure storage tanks, the main function of the emergency relief valve is to direct the gas directly into the atmosphere when the pressure inside the tank exceeds a preset value, thereby preventing the pressure from rising too high and causing dangerous incidents. If the emergency relief valve also has a negative pressure vacuum-breaking function, it indicates that the design takes into account the potential risks posed by a vacuum inside the tank; however, this is not a mandatory design requirement, so it may not be included in some design schemes. In summary, when designing atmospheric pressure storage tanks, comprehensive consideration should be given to the actual conditions and relevant regulatory requirements to ensure the safety and reliability of the tanks. .
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