Page 293 - Valve Selection Handbook

Table A-2.1 Section 1 Requirements
PRESSURE R ELIEF DEVICE OPERATING REQUIREMENTS
IO
ALLOWABLE VESSEL 00
OVERPRESSURE SET PRESSURE TOLERANCE o
(ABOVE MAWP OR VESSEL SPECIFIED PRESSURE WITH RESPECT TO SET REQUIRED
APPLICATION DESIGN PRESSURE) SETTINGS PRESSURE SLOWDOWN
SECTION 1 One valves MAWP ±2 psi up to and including 70 psi Minimum: 2% of set pressure or
6% (PG-67.2)* 2 psi whichever is greater
Others up to 3% above MAWP ±3% for pressures above 70 psi up
(PG-67.3) to and including 300 psi Maximum: 4% of set pressure or
4 psi whichever is greater, with
±10 psi for pressures above 300 some exceptions
psi up to and including 1000 psi (see PG-72)
±1 % for pressures above 1 000 psi
L (PG-72.2)
Forced Row Steam 20% (PG-67.4.2) May be set above MAWP; Valves Same as above Maximum: 10% of set pressure
Generators must meet overpressure (PG-72.2) (PG-72)
requirements (PG-67.4.2) s
*Note: References in parentheses are to Code paragraphs. 1 psi = 6.89 kPa »••
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Table A-2.2 Section III Requirements
I
PRESSURE RELJEF DEVICE OPERATING RE< aUIREMENTS I
ALLOWABLE VESSEL
OVERPRESSURE SET PRESSURE TOLERANCE s
(ABOVE MAWP OR VESSEL SPECIFIED WITH RESPECT TO SET REQUIRED
APPLICATION DESIGN PRESSURE) PRESSURE SETTINGS PRESSURE SLOWDOWN 3
SECTION III 10% above the design pressure of One valve £ design pressure Safely Valves Safety Values
any component within the ±2 psi for pressures up to and 95% of set pressure (maximum), I
NB pressure retaining boundary of the Additional valves higher provided including 70 psi or as specified in design
NC protected system limits on overpressure are specification &
ND maintained ±3% for pressures above 70 psi up (NB-7512.3)
NE (NB-7410) to and including 300 psi
(ND-7311b) (NC-7410)
(ND-7410) ±10 psi for pressures above 300 As specified in design specification
Overpressure may not exceed the psi up to and including 1000 psi (NC-7S12.3)
service or test limits specified in Valves must be set to operate (ND-7512.3)
the Design Specification within overpressure limits ±1% for pressures above 1000 psi (NE-7512.2)
(NE-7110a) (NE-7410) (NB-7512.2) (ND-7512.2)
(NC-7512.2)
Safety Relief and Relief Valves
±2% psi for pressures up to and Safety Relief and Relief Valves
As specified in design specification
including 70 psi
(NB-7513.1a) (ND-7513.1a) (NB-7513.2)
(NC-7513.2)
(NC-7513.1a) (NE-7512.1a)
(ND-7513.2)
±3% for pressures over 70 psi (NE-7S12.2)
(NB-7513.1a) (ND-7513.1a)
(NC-7513.13) (NE-7513.1a)
(Continued)
1 psi = 6.89 kPa