Valve leakage rate

A refinery operation produces about 500,000 barrels of crude per year. There are approximately 1500 gate valves used in the operation. Develop an estimate of the potential hydrocarbon emissions resulting from valve leakage. What is this worth in terms of lost revenues to the facility You can find some information on typical valve leakage rates from searching on w w w. google. com. 

Type C tests - tests to measure containment isolation valve leakage rates. 

Valve leakage rates are functions of the valve size and type of valve seat. Recommended valves and their maximum liquid leakage rate are presented in Table 4.3 [11]. 

The values presented in Table 4.3 are maximum allowable valve leakage rates according to API Std 598 [11] but may not be the actual valve leakage rates. However, the impact of valve leakage rate is not significant in overall calculations, and values presented in Table 4.3 can be used. 

Table 4.3 Maximum Valve Leakage Rates (for Liquid)...

The valve leakage rate is 2.08 10 m /sec per inch of pipe size. 

Leakage of the propellant through the valve is a critical parameter. Although the test is not required for metered valves in the USP, the leakage rate should be well characterized for leakage during development [6],... 

API Standard 527, Seat Tightness of Pressure Relief Valves This standard describes tests with air, steam and water to determine the seat tightness of metal- and soft-seated PRVs. Valves of conventional, bellows- and pilot-operated designs are covered. Acceptable leakage rates are defined for gas, steam and liquid. 

The set-up is shown in Figure 4.14. With the valve always mounted vertically, the leakage rate in bubbles per minute shall be determined with an inlet pressure held at 90% of the set pressure after the valve has been set and popped, except for valves set at or below 3.4 barg (50 psig), in which case the pressure shall be held at 0.34 barg (5 psig) below set pressure immediately after popping. The test pressure with air at atmospheric temperature shall be applied as follows ... 

Actually it is good practice that any valve received from an off-site location should be bench tested to verify set pressure and leakage rate. However, please be aware that if the tag on a new valve is broken, the supplier forfeits on the warranty of the valve unless it is done by or in the presence of a notified body who is able to tag or lead the valve again. 

Furthermore, the leakage rate is measured on helium (a far more searching gas than the methane or other gases the valve will see on site) it is somewhat difficult to transpose into relevant information the actual leakage rate the valve will have on, for instance, natural gas, which has a molecular weight much higher than helium. 

They will prevent the process components from leaking into the atmosphere, which can happen with relief valves. Conventional relief valves have an allowable leakage rate rupture disks do not. 

The containment system (this includes the piping, analyser cell and all related parts such as valves, flanges etc.), as the constructional part of an analyser which is permanently connected to the process to be monitored and which conducts the gas to be analysed, sometimes in combination with a carrier gas, shall be assessed with respect to its leakage rate (Table 7.1). If there is no oxygen present in this gas, air may be used for dilution. The air flow is... 

If the valve configuration is such that the fluid pressure assists closure, the leakage rate could conceivably decrease with increasing pressure. 

Control of leakage rate Metering-valve function... 

Table 6 shows the lower value of E for different liquid heights on the tray. This is the point at which liquid leakage through the valves begins. Values lower than that shown indicate leakage. This check does not calculate direct leakage rates. 

Plugging may be a problem in the water outlet line from the boot because of low flow rates and because solids and corrosion products tend to entrap in the boot and the water stream. The converse problem is leakage rates across the water outlet control valve exceeding the rate of water inflow into the boot. This makes maintaining boot level difficult and causes loss of product in the water stream. 

Specifications should insist that the maximum-allowed firing rate of a burner should be limited to 6 in. (151 mm) of water-column pressure drop across the bed when the excess air is above 15% as measured by flow devices on the air and fuel streams. The reason for 15% rather than 10% excess air is because of air and exhaust valve leakage. This leakage of combustion air cannot be used to burn fuel, but as long as the air loss is not greater than 10%, all the fuel can be burned in the furnace. 

If an actoator opens or closes with no closed actoators between it and either the inlet or the outlet, the transfer of fluid is made equally from or to both sides. Once the fluid volume is computed, the flow rate flows from the actuation frequency. Maximum head is taken to be the maximum pressure exerted by an actoator (though this is not often known), and efficiency is estimated from the actuation sequence. Often, an estimate of flow rate is all that is desired. It must be noted that these estimates are very coarse, with, for example, errors of a factor of two reported and attributed to unmodeled valve leakage [8]. 

Typical allowable primary containment leakage rates lie in the range of 0.1-1 per cent of volume a day, but the operating experience sometimes has indicated real-world values above these allowable limits. These are usually due to excessive valve or penetration leakage, valves or penetrations left open after testing, airlock failure, etc. 

The leakage rate assumed for the secondary containment room (systems, collection room or building) 1-10% per diem. (For this assumption to be valid extremely imlikely sequences are excluded, such as the rupture of a steam line with degraded core and valve leak proofing degraded.)... 

Leakage into the Safety Injection Tanks (SITs) by the two check valves isolating the tanks from the RCS is detected by an increase in pressure between the check valves. This pressure is indicated and alarmed in the control room. Secondarily, the SIT level would increase. The leakage rate would be computed from the rate of change of level. 

A simple feedback system can control the process pressure if a throttling valve is installed in the suction line between the process and the pump, as shown in Figure 23-21. The main problem with this system is that the reponse time is directly tied to the system leakage rate. If the leakage rate is high, response if fast but if the leakage rate is low, the response time will be very slow. Unfortunately, low leakage rate and fast response time is the most desirable combination. 

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