Safety valve is pressure equipment, containers and pipelines the best overpressure protection device, when the media pressure exceeds the allowable value, the safety valve automatically open, then the full amount of emissions, to prevent the pressure continues to rise, thus protecting the equipment and its operation Personnel safety; when the pressure is reduced to the specified value, the safety valve closed automatically in time to prevent the media continue to discharge, reduce losses. As the safety valve is an automatic valve, it is often used as the last protection device of the pressure equipment. In this sense, its role can not be replaced by other protective devices. First, the safety valve arrangement Safety valve should be installed upright and as close to the protected equipment or pipe. If not close to the arrangement, the total pressure drop across the pipe from the protected equipment or pipe to the safety valve inlet shall not exceed 3% of the pressure relief valve or 1/3 of the maximum allowable pressure drop Whichever is smaller), the pressure drop over the General Assembly led to safety valve frequent take-off. Commonly used in engineering practice to reduce pipeline pressure drop approach through the appropriate expansion of safety valve inlet diameter, the use of long-radius elbow, reducing the number of elbows to reduce the total pressure drop in the pipeline. Safety valve installation location should be the main consideration for easy maintenance. Therefore, the safety valve should be set at the maintenance platform, so that you can facilitate the piping is also easy to regularly check the safety valve, maintenance and calibration work. When arranging a heavy weight safety valve, consider the possibility of hoisting the safety valve after it is disassembled, if necessary, a boom and a site and space for maintenance and inspection. In engineering practice, it is common practice to install a safety valve on the top of a pipe gallery. In this way, on the one hand higher than the vent Explorer, on the other hand safety valve centralized arrangement in the top of the gallery to facilitate maintenance. Due to special reasons difficult to install the container body, consider installing it in the outlet pipe, but the pipeline between the safety valve installation and container should avoid sudden turn, partial contraction of the cross-section structure, should prevent the increase in the pipeline Resistance, causing the accumulation of dirt clogging and so on. Second, the safety valve inlet piping design Safety valve inlet piping design should be short and straight, and should adopt a long radius elbow. The pipeline must be at least 5% of the slope, the slope of the protected system; inlet pipeline to be calculated in the operating temperature range whether the need for compensation. The inlet pipe should avoid pouch bending, if it can not be avoided, the drain pipe with continuous flow at the low point of the pouch is connected to the same pressure system. If the condensate becomes thick or solid, then Drains to be traced; for non-condensable media, at the lowest point in the bag-shaped bend easy to close the operation of the release valve. Imported pipe channel minimum cross-sectional area should not be less than the safety valve inlet cross-sectional area. In the case of high pressure and large displacement, the inlet pipe should have a sufficiently large fillet radius at the inlet or conical passages with an inlet cross-sectional area approximately twice that of the outlet cross-sectional area. Imported pipe should have sufficient strength and appropriate support bracket to withstand the medium pressure, temperature and safety valve discharge reaction force and other common stress; At the same time to avoid the transmission of equipment to the safety valve vibration, affecting the safety valve seal. Third, the safety valve outlet pipe design Safety valve outlet pipe should be designed to consider the back pressure does not exceed the pressure relief valve certain value. For ordinary spring-type safety valve, the back pressure does not exceed 10% of the pressure relief valve. For the liquid medium safety valve outlet pipe outlet pipe should be as much higher than the vent, mainly to avoid condensate back to the normal use of safety valve. When discharged to the vent or to the torch main medium with condensate or condensable gas, the safety valve outlet should also be higher than the mains. Otherwise, automatic drainage should be considered. Engineering practice, generally through the condensate drain access to the accumulator tank and then through the pump or gas purge to the liquid separation tank centralized treatment. The safety valve outlet pipe to the flare main should be miter-connected to the top of the discharge pipe at a flow rate of 45 degrees to prevent the condensate from flowing back into the main pipe and reduce the back pressure of the safety valve. Due to the discharge of material, the discharge of material will exert a certain force on the discharge pipe and will be delivered to the safety valve through the discharge pipe. The resulting force and torque will have an adverse effect on the equipment nozzle and the safety valve inlet and outlet pipes and may even cause Leakage of safety valve seals creates an accident. Therefore, the relief valve should be exported to calculate the reaction force, and considering their own weight, vibration, wind load, thermal expansion and contraction and other factors set the appropriate stent support. Fourth, before and after the safety valve cut-off valve and bypass valve settings 1. Safety valve before and after the cut-off valve set in the production of enterprises, the safety valve replacement, the equipment does not necessarily stop production, so most of the enterprises in order to ensure the production, before the safety valve Install shut-off valve. Generally should use a single gate valve, and lead seal open, the stem should be installed horizontally, so as to prevent the valve stem and valve plate connected pin corrosion or loose valve plate fell. When the safety valve test expires, after take-off damage, you can close the safety valve inlet shut-off valve, remove the safety valve for verification or replacement. According to the actual production experience, the installation of the main cut-off valve before the main situation is: 1.1 safety valve in the normal production of valve leakage and over-pressure can not be reset after opening. 1.2 to facilitate technical supervision departments in the production of safety valves for monitoring. 1.3 Important equipment, processes directly affect the production system to open stop, causing economic losses to the enterprise. 1.4 Production or storage of polluting or hazardous gases and liquids equipment and devices. For safety valves that are vented to a flare or containment system, a shut-off valve is normally installed on the outlet pipe of the safety valve and sealed open, even if the outlet piping does not require a by-pass, in order to cut the torch or containment system when the safety valve malfunctions , Otherwise the entire torch or closed system should be suspended. 2. Safety valve bypass setting Safety valve bypass setting is not necessary. The purpose of setting the safety valve bypass is to allow the safety valve protected equipment and systems to be repaired without downtime. Only those important safety valves that require on-line maintenance and can not be shut down need to be bypassed. If the safety valve protection equipment and systems can stop working in the safety valve failure cut-off operation and maintenance, you do not need to set the bypass. Another function of the bypass is to open the by-pass purge to the flare system when the equipment and system are steam purged while on-time. Safety valve bypass installed in the safety valve inlet and outlet line shut-off valve outside (shut-off valve between the bypass and the safety valve), generally with the inlet diameter; preferably in the safety valve near the system installed on the pipeline pressure gauge, This allows you to monitor system pressure at any time. V. Summary In this paper, the arrangement principle of safety valve and piping design requirements were discussed. Safety valve is the most common and important protection device in modern pressure equipment, which is of great significance to the safe operation of equipment and equipment. The actual application of the process should be its layout and piping design caused enough attention.
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