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AS 1271-2003


Safety valves, other valves, liquid level gauges and other fittings for boilers and unfired pressure vessels

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Specifies requirements for the design, construction and testing of safety valves, other valves, liquid relief valves, liquid level gauges, blowdown valves and other fittings for use on boilers and unfired pressure vessels and their associated piping.
Published: 18/08/2003
Pages: 51
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Table of contents
Cited references
Content history
Table of contents
About this publication
1 Scope and general
1.1 Scope
1.2 Application
1.3 Referenced documents
1.4 Definitions
1.5 Pressures
1.6 Designation
2 General valve design, construction and application
2.1 Materials
2.1.1 Material standards
2.1.2 Suitability
2.1.3 Limits of application
2.1.4 Castings and forgings
2.1.5 Repair of castings
2.1.6 Impregnation of castings
2.2 Construction
2.2.1 Bonnet and cover joint
2.2.2 Stems and stuffing boxes
2.2.3 Ball valve, plug cock, or cock
2.2.4 Moving parts
2.3 Pressure/temperature design and rating
2.3.1 Pressure/temperature rating
2.3.2 Modified rating due to connections
2.3.3 Determination of dimensions
2.3.4 Design strength
2.3.5 Valve and fitting scantlings
2.3.6 Proof test
2.3.7 Local reductions
2.4 Valve mounting and connections
2.4.1 Flanged connections
2.4.2 Butt‑welded connections
2.4.3 Threaded connections
2.4.4 Socket-welded connections
2.4.5 Other connections
2.5 Marking and documentation
2.5.1 Direction of flow
2.5.2 Direction of operation
2.5.3 Open/shut indicators
2.5.4 Data
2.5.5 Additional marking—safety and relief valves
2.5.6 Records and certification—safety and relief valves
2.6 Hydrostatic tests
2.6.1 Hydrostatic test fluid
2.6.2 Body test
2.6.3 Seat test
3 Safety and relief valves
3.1 General
3.1.1 Scope of section
3.1.2 Fail‑safe
3.1.3 Stem seals
3.1.4 Locking of adjustments
3.1.5 Drainage
3.1.6 Freedom of operation
3.2 Spring loading
3.2.1 Springs Design Workmanship Spacing of coils Height/diameter ratio Finish Marking
3.2.2 Range of application
3.2.3 Prevention to alteration of set pressure
3.3 Easing gear
3.3.1 Provision of easing gear
3.3.2 Lifting pressure
3.4 Operation
3.4.1 Smooth operation
3.4.2 Tolerances and limits on valve characteristics
3.5 Capacity rating, classification, and certification
3.5.1 Method of rating
3.5.2 Classification
3.5.3 Certification
3.5.4 Other certification
3.6 Testing for operating and flow characteristics for safety valves using steam, air, water, or other gases or liquids of known characteristics
3.6.1 Operating and flow characteristics to be tested
3.6.2 Testing of valves
3.6.3 Coefficient of discharge
3.6.4 Design changes
3.6.5 Records of test
3.7 Tests to determine operating characteristics
3.7.1 Test equipment
3.7.2 Valves used in the test programme
3.7.3 Test procedure
3.8 Tests to determine flow characteristics
3.8.1 Carrying out of tests
3.8.2 Flow test equipment
3.8.3 Valves used in the test programme
3.8.4 Test procedure
3.8.5 Adjustments during test
3.8.6 Records and test results
3.9 Measurement of lift
3.9.1 Carrying out measurement
3.9.2 Measuring equipment
3.9.3 Valves used in measurement programme
3.9.4 Measurement procedure
3.9.5 Records
3.10 Rated discharge capacity
3.10.1 Class A valves
3.10.2 Class B valves
3.10.3 Pilot operation
4 Liquid relief valves
4.1 General
4.2 Rated discharge capacity
5 Liquid level gauges
5.1 Scope of section
5.2 Mountings
5.3 Gauge glasses
5.4 Drain
5.5 Cock handles
5.6 Guards
5.7 Safety devices
5.8 Connection to pressure vessel
6 Blowdown valves
6.1 Design
6.2 Operation
Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F
F1 Scope
F2 Coefficient of discharge (α)
F3 Discharge capacity for steam
F4 Discharge capacity for air or any gas or vapour
F4.1 Critical and subcritical flow
F4.2 Equations
F4.3 Discharge capacity for real gases
F4.4 Discharge capacity for incompressible fluids
Appendix G
G1 Scope
G2 Equation
Appendix H
Amendment control sheet
Cited references in this standard
Pipe threads of Whitworth form, Part 1: Sealing pipe threads (metric units)
Sizing, selection and installation of pressure-relieving devices in refineries, Part 1: Sizing and selection
Hydrostatic testing of steel valves
BS 3799
Specification for steel pipe fittings, screwed and socket-welding for the petroleum industry
BS 3463
Specification for observation and gauge glasses for pressure vessels
Content history
DR 02299
AS 1271-2003 Rec:2016