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API RP 576-2009 pdf free download

API RP 576-2009 pdf free download.Inspection of Pressure-relieving Devices.
3.2 Dimensional Characteristics of Pressure-relief Valves 3.2.1 effective discharge area A nominal or computed area used with an effective discharge coefficient to calculate the minimum required relieving capacity for a pressure-relief valve per the preliminary sizing equations contained in API 520. Refer to API 520-1 for the preliminary sizing equations. API 526 provides effective discharge areas for a range of sizes in terms of letter designations, “D” through “T.” 3.2.2 huddling chamber An annular pressure chamber located downstream of the seat of a pressure-relief valve, for the purpose of assisting the valve to achieve lift. 3.2.3 inlet size The nominal pipe size (NPS) of the relief device at the inlet connection, unless otherwise designated. 3.2.4 lift The actual travel of the disk away from the closed position when a pressure-relief valve is relieving. 3.2.5 outlet size The nominal pipe size (NPS) of the relief device at the discharge connection, unless otherwise designated. 3.3 Operational Characteristics—System Pressures 3.3.1 accumulation The pressure increase over the MAWP of the vessel allowed during discharge through the pressure-relief device, expressed in pressure units or as a percentage of MAWP or design pressure. Maximum allowable accumulations are established by applicable codes for emergency, operating, and fire contingencies.
3.3.2 design pressure The design pressure of the vessel along with the design temperature is used to determine the minimum permissible thickness or physical characteristic of each vessel component, as determined by the vessel design rules. The design pressure is selected by the user to provide a suitable margin above the most severe pressure expected during normal operation at a coincident temperature. It is the pressure specified on the purchase order. This pressure may be used in place of the MAWP in all cases where the MAWP has not been established. The design pressure is equal to or less than the MAWP. 3.3.3 maximum allowable working pressure MAWP The maximum gauge pressure permissible at the top of a completed vessel in its normal operating position at the designated coincident temperature specified for that pressure. The pressure is the least of the values for the internal or external pressure as determined by the vessel design rules for each element of the vessel using actual nominal thickness, exclusive of additional metal thickness allowed for corrosion and loadings other than pressure. The MAWP is the basis for the pressure setting of the pressure-relief devices that protect the vessel. The MAWP is normally greater than the design pressure but can be equal to the design pressure when the design rules are used only to calculate the minimum thickness for each element and calculations are not made to determine the value of the MAWP.
3.4.7 cold differential test pressure CDTP The pressure at which a pressure-relief valve is adjusted to open on the test stand.The CDTP includes corrections for the service conditions of backpressure or temperatures or both. 3.4.8 leak-test pressure The specified inlet static pressure at which a seat leak test is performed. 3.4.9 manufacturing design range The pressure range at which the rupture disk shall be marked. Manufacturing design ranges are usually catalogued by the manufacturer as a percentage of the specified burst pressure. Catalogued manufacturing ranges may be modified by agreement between the user and the manufacturer. 3.4.10 marked burst pressure or rated burst pressure The marked burst pressure or rated burst pressure of a rupture disk is the burst pressure established by tests for the specified temperature and marked on the disk tag by the manufacturer. The marked burst pressure may be any pressure within the manufacturing design range unless otherwise specified by the customer. The marked burst pressure is applied to all the rupture disks of the same lot. 3.4.11 opening pressure The value of increasing inlet static pressure whereby there is a measurable lift of the disk or at which discharge of the fluid becomes continuous, as determined by seeing, feeling or hearing. 3.4.12 set pressure The inlet gauge pressure at which a pressure-relief valve is set to open under service conditions. 3.4.13 simmer The audible or visible escape of compressible fluid between the seat and disc, which may occur at an inlet static pressure below the set pressure prior to opening.

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