Set up a pressure relief manhole or a hydraulic safety valve
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In a subsidiary of a fine chemicals factory, there are fixed-roof tanks with a capacity of 50 cubic meters, used to store Class A and B liquids. A nitrogen purge system has been installed as required. In accordance with the requirements of GB50160-2008 (which do not apply to version 92), accident relief devices such as pressure relief vents and breathing vents must be installed to ensure the safety of these tanks. By checking the drawings, it appears that a hydraulic safety valve is used (it’s just a guess; there’s no indication of this on the first page of the drawings). When asked, they explained that the tank was too small to accommodate a manhole on top. In accordance with SY/T 0511.2-2010 \"Attachments for Oil Storage Tanks – Part 2: Hydraulic Safety Valves\" and other relevant regulations, hydraulic safety valves with the same diameter as flame arresters and vent valves have been installed. After reviewing relevant information, hydraulic safety valves are designed to prevent mechanical failures in flame arresters and vent valves; their maximum size is DN350. On the other hand, emergency relief manholes are intended to prevent fires, and they have a larger discharge capacity, with a minimum size of DN500. Therefore, hydraulic safety valves cannot replace pressure relief manholes, right? Earlier versions of SH3007-1999 included provisions regarding hydraulic safety valves, but there are no such provisions in versions from 2007 onward. Is bringing this up now just a repetition of old topics? Can it meet the requirements of current standards?
Safety valves are not seen to be installed on atmospheric pressure storage tanks. They usually include an exhaust valve, positive and negative pressure water seal tanks, and pressure relief manholes. At the site, breath valves are the most common to be seen ； Those with pressure relief manholes usually contain heavy oil components, and the breather valves may get clogged ； Water seal tanks were not commonly used in the past; it is only in recent years, due to efforts to control VOCs, that storage tanks have been sealed, leading to an increase in their use. The order of protection is positive and negative pressure water seal tanks (with the lowest pressure threshold for failure), exhaust valves, and pressure relief manholes. .
SY/T 0511.2-2010 \"Attachments for oil storage tanks – Part 2: Hydraulic safety valves\" states that hydraulic safety valves are intended to replace the function of breather valves, and not for pressure relief in case of fires.
On floor 18 of the post at https://bbs.hcbbs.com/thread-1922865-2-1.html, ljz7792651 wrote the following: Based on our experience, for atmospheric pressure storage tanks with a capacity of 200 cubic meters or less (where the material requires nitrogen sealing), the basic configuration includes: 1. Nitrogen supply valve + nitrogen release valve + vent valve； 2. Nitrogen supply valve + breather valve + hydraulic safety valve ； Atmospheric storage tanks of 200 cubic meters or more (where the material requires nitrogen sealing), basic configuration: 1. Nitrogen supply valve + nitrogen release valve + breather valve ； 2. Nitrogen supply valve + breather valve + hydraulic safety valve ； 3. Nitrogen supply valve + vent valve + safety manhole (emergency release manhole). The above are just based on experience. It ultimately depends on the parameters of the storage tank; it is necessary to perform flow calculations for the nitrogen supply valve, nitrogen release valve, breather valve, and emergency relief manhole to determine whether they can meet the specific requirements. The role of the breather valve depends on the configuration at the top of the storage tank; if Configuration 1 is considered, then the breather valve can be regarded as a safety measure ； If Configuration 2 is considered, then the breather valve is a process valve, while the hydraulic safety valve is a safety measure ； If considering Device 3, then the breathing valve is also a process valve, while the emergency relief manhole is a safety measure. It can be used as a reference, but I’m not sure if experts will approve it
Petroleum Regulation 6.2.19 is indeed quite annoying. Class A and B storage tanks equipped with nitrogen sealing must have emergency pressure relief measures; obviously, a breather valve is a process valve, not an emergency release valve. This emergency pressure relief measure typically involves an emergency pressure relief manhole, and the ventilation capacity of such a manhole is calculated based on fire conditions; it has nothing to do with nitrogen sealing. Is it true that fires are more likely to occur when a nitrogen seal is in place? Another issue is the size of the storage tank mentioned by the poster; does a very small nitrogen seal tank even come equipped with an emergency pressure relief manhole? The minimum size for such manholes is DN450, which doesn’t seem appropriate in this case. Complain a bit. . .
Hydraulic safety valves must not be confused with mechanical safety valves
Based on personal engineering experience, pressure relief manholes can encounter problems in extremely cold regions during winter when snow accumulates on the top of the tank. Hydraulic safety valves can effectively maintain a stable operating pressure of the equipment in cases where the vent valves and flame arresters on the tank top become frozen and stop functioning. However, the volatility is high under accident conditions, and the hydraulic safety valve may not meet the requirements. In light of the above, it is recommended that companies with the necessary resources install both hydraulic safety valves and pressure relief manholes. This approach helps to prevent problems such as collapse or overpressure resulting from the failure of flame arresters on breathing valves and vent pipes, and it also helps to avoid the risk of overpressure in the tank due to the rapid evaporation of gaseous components when adjacent equipment catches fire.
It clearly states that there is an emergency exhalation function in case of a fire
The pressure relief manhole for this purpose is probably not intended for use in fire conditions, right?