Atmosphere, relieving

Ensure vents relieve to a safe location. If vented to atmosphere, ensure proper classification and controlled access... 

It is shown that solute atoms differing in size from those of the solvent (carbon, in fact) can relieve hydrostatic stresses in a crystal and will thus migrate to the regions where they can relieve the most stress. As a result they will cluster round dislocations forming atmospheres similar to the ionic atmospheres of the Debye- Huckel theory ofeleeti oly tes. The conditions of formation and properties of these atmospheres are examined and the theory is applied to problems of precipitation, creep and the yield point."... 

Examples of such backup features are given for each utility below. In designs where all pressure rehef valves discharge into a closed collection system, because of environmental restrictions, a total failure of one utility deserves more careful consideration since there are no atmospheric releases which would tend to relieve the load on the closed system. 

It should be noted that the above maximum radiant heat density criteria for application to inadvertently ignited atmospheric releases from pressure relief valves or vents are less restrictive than those used for flare design. This results from the fact that flares are continuously ignited, whereas ignition of a relieving PR valve is unlikely. In addition, the area surrounding a flare is open and offers no protection, while within a process unit access to shelter is available. 

The most important safety devices in a production facility are the pressure relief valves, which ensure that pipes, valves, fittings, and pressure vessels can never be subjected to pressures higher than their design pressures. Relief valves must be designed to open rapidly and fully, and be adequately sized to handle the total flow of gas and liquids that could potentially cause an overpressure situation. They relieve the pressure by routing this stream to a safe location where it can be vented to atmosphere or burned. 

Conventional relief valves should only be used where the discharge is routed independently to atmosphere, or if installed in a header system, the back-pressure build-up when the device is relieving must be kept below 10% of the set pressure so the set point is not significantly affected. The set point increases directly with back-pressure. 

The pressure in the relief piping is usually equal to atmospheric pressure as long as no relief valve is relieving. There is a common miscon-... 

Testing of pressure relieving spring loaded valves at atmospheric temperature requires an adjustment in set pressure at ambient conditions to compensate for higher operating temperatures. For process services see Table 7-UV and for saturated steam, use Table 7-1B. 

F2 = coefficient of subcrilical flow, see Figure 7-29 T = relieving temperature of inlet gas or vapor, °R P = upstream relieving pressure, psia, = set pressure + allowable overpressure + atmospheric pressure, usually 14.7 psia), psia P2 = backpressure on valve, psia W = required flow through valve, Ibs/hr V = vapor flow required through valve, standard cu ft/min at 14.7 psia and 60°F... 

Pj = upsueain relieving pressure, in pounds per square inch absolute. This is the set pressure plus the allowable overpressure plus the atmospheric pressure. 

These explosions in air are usually the result of the release of flammable gas and/or mists by leaks, rupture of equipment, or rupture of safety relieving devices and release to the atmosphere, which become ignited by spark, static electricity, hot surfaces, and many other... 

An emergency relief valve is installed on a reactor to relieve excess pressure in case of a runaway reaction. The lines upstream and downstream of the valve are 6 in. sch 40 pipe. The valve is designed to open when the tank pressure reaches 100 psig, and the vent exhausts to the atmosphere at 90° to the direction entering the valve. The fluid can be assumed to be incompressible, with an SG of 0.95, a viscosity of 3.5 cP, and a specific heat of 0.5 Btu/(lbm °F). If the sum of the loss coefficients for the valve and the vent line is 6.5, determine ... 

Pressure relief devices relieving directly to the atmosphere Use calculated total release rate at set pressure. Refer to pressure relief calculation. All material released is assumed to be airborne. 

If flammable gases are likely to be relieved to the atmosphere, the relief stream either cannot reach a source of ignition or, if ignited, it must bum harmlessly. Dilution of the relief stream to a point below the lower flammability limit is highly recommended. A review paper [231] provides details on solving this general problem. 

The pressure relief device should be evaluated and sized in accordance with the latest industry standards (i.e., DIERS, API, NFPA). An open passage (nozzle or line) from the separator to the atmosphere may be considered as the pressure relief device provided that it meets the relieving capacity requirements of the ASME Boiler and Pressure Vessel Code (BPVC). 

Since discharges of vapors from highly hazardous materials cannot simply be released to the atmosphere, the use of a weak seam roof is not normally acceptable. It is best that tanks in low-pressure hazardous service be designed and stamped for 15 psig to provide maximum safety, and pressure relief systems must be provided to vent relieved overpressure to equipment tfiat can collect, contain, and treat the effluent. 

Only when other alternatives are not available should a fluid release to the open environment be considered a viable disposal method. Additionally it should only be considered when the release is small and does not create an additional hazard - either from fire safety or environmentally. The relieved liquid should always be directed to a level surface away from other equipment, for containment by the facility surface runoff accommodations to mitigate any environmental or fire hazard. In no cases should discharge to the atmosphere be contemplated as it would create an immediate explosion or fire hazard and could also be considered an immediate environmental pollutant. 

The outside surfaces of refrigerated storage vessels are thermally insulated to assist in maintaining the desired storage temperature. Thermal excursions increase product vaporization, raise vessel pressure, and increase the amount of gas relieved to atmosphere orto a relief vent collection system. Fire exposure of a refrigerated vessel can increase product temperature and vessel pressure, possibly exceeding the capacity of relief valves or relief vent collection system, and could result in vessel rupture with major fire or explosion consequences. 

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