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Does the emergency relief valve need to have a negative pressure vacuum breaking function?

2023-04-24View Original

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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?
Reply #22023-04-24
According to the relevant specifications and documents you provided, when designing a pressure vessel at atmospheric pressure and with nitrogen sealing in place, the negative-pressure vacuum-breaking function of the emergency relief valve is not necessary. Since the emergency pressure relief equipment already meets the ventilation requirements necessary to ensure the safety of the storage tank and can directly connect to the atmosphere, it will activate automatically in case of a failure of the breather valve to release pressure, thereby preventing any issue with negative pressure. Nor is there any requirement in Sinopec’s Letter on Refining and Production [2016] No. 127 that the emergency relief valve must have a negative pressure vacuum-breaking function. .

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