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API RP 576 (2017) Terms/Definitions - Flashcards -

Terms in this set (29)

3.1 Accumulation
The pressure increase over the maximum allowable working pressure (MAWP) of the vessel or piping system, expressed in pressure units or as a percentage of MAWP or design pressure if a MAWP has not been established.
3.2 Backpressure
The pressure that exists at the outlet of a pressure-relief device as a result of the pressure in the discharge system. The sum of the superimposed and built-up backpressures.
3.3 Blowdown
The difference between the set pressure and the closing pressure of a pressure-relief valve, expressed as a percentage of the set pressure or in pressure units.
3.4 Built-up Backpressure
The increase in pressure at the outlet of a pressure-relief device that develops as a result of flow after the pressure-relief device opens.
3.5 Burst Pressure
The value of the upstream static pressure minus the value of the downstream static pressure just prior to when the disk bursts. When the downstream pressure is atmospheric, this is the upstream static gauge pressure.
3.6 Burst Pressure Tolerance
The variation around the marked burst pressure at the specified disk temperature in which a rupture disk will burst.
3.7 Car Seal
A device installed on a valve to secure it in a specified position (open or closed). When properly installed, the associated valve cannot be operated unless this is physically removed.
3.8 Closing Pressure
The value of decreasing inlet static pressure at which the valve disc reestablishes contact with the seat or at which lift becomes zero, as determined by seeing, feeling, or hearing.
3.9 Cold Differential Test Pressure - CDTP
The pressure at which a pressure-relief valve is adjusted to open on the test stand. Includes corrections for the service conditions of superimposed backpressure or temperature or both.
3.10 Design Pressure
The pressure, together with the design temperature, used to determine the minimum permissible thickness or physical characteristic of each vessel component as determined by the vessel design rules. This pressure may be used in place of the MAWP in all cases where the MAWP has not been established. Equal to or less than the MAWP.
3.11 Galling
A condition whereby excessive friction between high spots results in localized welding with subsequent splitting and a further roughening of rubbing surfaces of one or both of two mating parts.
3.12 Huddling Chamber
An annular chamber located downstream of the seat of a pressure-relief valve for the purpose of assisting the valve to achieve lift.
3.13 Lift
The actual travel of the disc away from the closed position when a pressure-relief valve is relieving.
3.14 Lifting Lever
A device on the relief valve that applies external force to the stem of the relief valve, which can be used to manually operate the valve.
3.15 Manufacturing Design Range
The pressure range at which the rupture disk shall be marked. Usually catalogued by the manufacturer as a percentage of the specified burst pressure. May be modified by agreement between the user and the manufacturer.
3.16 Marked Burst Pressure
The burst pressure established by tests for the specified temperature and marked on the disk tag by the manufacturer. May be any pressure within the manufacturing design range unless otherwise specified by the customer and is applied to all of the rupture disks of the same lot.
3.17 Maximum Allowable Working Pressure - MAWP
The maximum gauge pressure permissible at the top of a vessel in its operating position at the designated coincident temperature specified for that pressure.
3.18 Nonreclosing Pressure-Relief Device
A pressure-relief device that remains open after operation. A manual resetting means may be provided.
3.19 Opening Pressure
The value of increasing inlet static pressure whereby there is a measurable lift of the disc or at which discharge of the fluid becomes continuous, as determined by seeing, feeling, or hearing.
3.20 Overpressure
The pressure increase over the set pressure of the relieving device. Expressed in pressure units or as a percentage of set pressure. This is the same as accumulation only when the relieving device is set to open at the MAWP of the vessel.
3.21 Pin-Actuated Device
A nonreclosing pressure-relief device actuated by static pressure and designed to function by buckling or breaking a pin that holds a piston or a plug in place. Upon buckling or breaking of the pin, the piston or plug instantly moves to the full open position.
3.22 Pop Pressure
The value of increasing inlet static pressure at which the disc moves in the opening direction at a faster rate as compared with corresponding movement at higher or lower pressures.
3.23 Qualified Person
A competent person who has met the knowledge, skill requirements and expectations of the owner-user.
3.24 Set Pressure
The inlet gauge pressure at which a pressure-relief valve is set to open under service conditions.
3.25 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.
3.26 Specified Burst Pressure
Specified by the user. The marked burst pressure may be greater than or less than this, but shall be within the manufacturing design range.
3.27 Superimposed Backpressure
The static pressure that exists at the outlet of a pressure-relief device at the time the device is required to operate. It is the result of pressure in the discharge system coming from other sources and may be constant or variable.
3.28 Telltale Indicator
An assembly installed in the space between a rupture disk and another relief device (in series) to detect or prevent the accumulation of pressure between the rupture disk and the other device.
3.29 Trim
Refers to internal parts of a pressure-relief valve that are manufactured using materials that are resistant to degradation from the associated process.
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