AS 1271-1997

1 - AS 1271-1997 SAFETY VALVES, OTHER VALVES, LIQUID LEVEL GAUGES AND OTHER FITTINGS FOR BOILERS AND UNFIRED PRESSURE VESSELS
4 - PREFACE
5 - CONTENTS
7 - SECTION 1 SCOPE AND GENERAL
7 - 1.1 SCOPE
7 - 1.2 APPLICATION
7 - 1.3 REFERENCED DOCUMENTS
8 - 1.4 DEFINITIONS
8 - 1.4.1 Assisted safety valve
8 - 1.4.2 Blowdown (in relation to safety and relief valves)
8 - 1.4.3 Built-up backpressure
8 - 1.4.4 Certified capacity
8 - 1.4.5 Coefficient of discharge (a)
8 - 1.4.6 Cold differential test pressure
9 - 1.4.7 Commencement of lift
9 - 1.4.8 Corrosion
9 - 1.4.9 Design pressure
9 - 1.4.10 Direct-loaded safety valve
9 - 1.4.11 Equivalent calculated capacity
9 - 1.4.12 Fitting
9 - 1.4.13 Inlet size
9 - 1.4.14 Inspector
9 - 1.4.15 Lift
9 - 1.4.16 Manufacturer
9 - 1.4.17 Nominal pressure (PN)
9 - 1.4.18 Nominal size (DN)
9 - 1.4.19 Overpressure (in relation to safety and relief valve)
9 - 1.4.20 Pilot-operated safety valve
9 - 1.4.21 Plug cock (cock)
10 - 1.4.22 Purchaser
10 - 1.4.23 Relief valve
10 - 1.4.24 Relieving pressure (flow rating pressure)
10 - 1.4.25 Re-seating (in relation to safety and relief valve)
10 - 1.4.26 Safety valve
10 - 1.4.27 Set pressure (in relation to safety and relief valve)
10 - 1.4.28 Shall
10 - 1.4.29 Should
10 - 1.4.30 Superimposed backpressure
10 - 1.4.31 Supplementary-loaded safety valve
10 - 1.4.32 Theoretical flowing (discharge) capacity
10 - 1.5 PRESSURES
10 - 1.6 DESIGNATION
11 - SECTION 2 GENERAL DESIGN AND CONSTRUCTION
11 - 2.1 MATERIALS
11 - 2.1.1 Material standards
11 - 2.1.2 Suitability
11 - 2.1.3 Limits of application
11 - 2.1.4 Castings and forgings
11 - 2.1.5 Repair of castings
11 - 2.1.6 Impregnation of castings
11 - 2.2 PRESSURE/TEMPERATURE DESIGN AND RATING
11 - 2.2.1 Pressure/temperature rating
12 - 2.2.2 Modified rating due to connections
12 - 2.2.3 Determination of dimensions
12 - 2.2.4 Design strength
12 - 2.2.5 Method of calculation
12 - 2.2.6 Proof test
12 - 2.2.7 Local reductions
12 - 2.3 MOUNTING AND CONNECTIONS
12 - 2.3.1 Flanged connections
12 - 2.3.2 Butt-welded connections
12 - 2.3.3 Threaded connections
12 - 2.3.4 Type of thread
13 - 2.3.5 Socket-welded connections
13 - 2.3.6 Other connections
13 - 2.4 BOLTING
13 - 2.5 DESIGN AND CONSTRUCTION
13 - 2.5.1 Integrity of design
13 - 2.5.2 Securing of seats
13 - 2.5.3 Bonnet and cover joint
14 - 2.5.4 Stems and stuffing boxes
14 - 2.5.5 Ball valve, plug cock, or cock
14 - 2.5.6 Moving parts
14 - 2.6 MARKING AND DOCUMENTATION
14 - 2.6.1 Direction of flow
14 - 2.6.2 Direction of operation
14 - 2.6.3 Open/shut indicators
14 - 2.6.4 Data
15 - 2.6.5 Additional marking -safety and relief valves
15 - 2.6.6 Records and certification -safety and relief valves
15 - 2.7 HYDROSTATIC TESTS
15 - 2.7.1 Hydrostatic test fluid
15 - 2.7.2 Body test
16 - 2.7.3 Seat test
18 - SECTION 3 SAFETY AND RELIEF VALVES
18 - 3.1 GENERAL
18 - 3.1.1 Scope of section
18 - 3.1.2 Fail-safe
18 - 3.1.3 Stem seals
18 - 3.1.4 Locking of adjustments
18 - 3.1.5 Drainage
18 - 3.1.6 Freedom of operation
18 - 3.2 SPRING LOADING
18 - 3.2.1 Springs
19 - 3.2.2 Range of application
19 - 3.2.3 Prevention to alteration of set pressure
19 - 3.3 EASING GEAR
19 - 3.3.1 Provision of easing gear
19 - 3.3.2 Lifting pressure
19 - 3.4 OPERATION
19 - 3.4.1 Smooth operation
19 - 3.4.2 Tolerances on valve characteristics
20 - 3.5 CAPACITY RATING, CLASSIFICATION, AND CERTIFICATION
20 - 3.5.1 Method of rating
20 - 3.5.2 Classification
20 - 3.5.3 Certification
20 - 3.5.4 Other approval
21 - 3.6 TESTING FOR OPERATING AND FLOW CHARACTERISTICS FOR SAFETY VALVES USING STEAM, AIR, WATER, OR OTHER GASES OR LIQUIDS OF KNOWN
21 - 3.6.1 Operating and flow characteristics to be tested
21 - 3.6.2 Testing of valves
21 - 3.6.3 Information to be supplied to the purchaser
21 - 3.6.4 Coefficient of discharge
21 - 3.6.5 Design changes
21 - 3.6.6 Records of test
21 - 3.7 TESTS TO DETERMINE OPERATING CHARACTERISTICS
21 - 3.7.1 Test equipment
22 - 3.7.2 Valves used in the test programme
22 - 3.7.3 Test procedure
22 - 3.8 TESTS TO DETERMINE FLOW CHARACTERISTICS
22 - 3.8.1 Carrying out of tests
22 - 3.8.2 Flow test equipment
22 - 3.8.3 Valves used in the test programme
22 - 3.8.4 Test procedure
23 - 3.8.5 Adjustments during test
23 - 3.8.6 Records and test results
23 - 3.9 MEASUREMENT OF LIFT
23 - 3.9.1 Carrying out measurement
23 - 3.9.2 Measuring equipment
23 - 3.9.3 Valves used in measurement programme
23 - 3.9.4 Measurement procedure
24 - 3.9.5 Records
24 - 3.10 RATED DISCHARGE CAPACITY
24 - 3.10.1 Class A valves
24 - 3.10.2 Class B valves
26 - 3.10.3 Pilot operation
27 - SECTION 4 LIQUID RELIEF VALVES
27 - 4.1 GENERAL
27 - 4.2 RATED DISCHARGE CAPACITY
28 - SECTION 5 LIQUID LEVEL GAUGES
28 - 5.1 SCOPE OF SECTION
28 - 5.2 MOUNTINGS
28 - 5.3 GAUGE GLASSES
28 - 5.4 DRAIN
28 - 5.5 COCK HANDLES
28 - 5.6 GUARDS
28 - 5.7 SAFETY DEVICES
28 - 5.8 CONNECTION TO PRESSURE VESSEL
29 - SECTION 6 BLOWDOWN VALVES
29 - 6.1 DESIGN
29 - 6.2 OPERATION
30 - APPENDIX A - MINIMUM THICKNESS OF SAND-CAST VALVES AND OTHER FITTINGS
32 - APPENDIX B - PROPOSED TEST REPORT FOR SAFETY VALVE
34 - APPENDIX C - FORM FOR CERTIFICATE-CLASS A SAFETY VALVES
35 - APPENDIX D - FORM FOR CERTIFICATE-CLASS B SAFETY VALVES
36 - APPENDIX E - PRESSURE/TEMPERATURE TRANSFER CURVE
39 - APPENDIX F - DISCHARGE CAPACITY
39 - F1 SCOPE
39 - F2 COEFFICIENT OF DISCHARGE (a)
39 - F3 DISCHARGE CAPACITY FOR STEAM
42 - F4 DISCHARGE CAPACITY FOR AIR OR ANY GAS OR VAPOUR
42 - F4.1 Critical and subcritical flow
42 - F4.2 Equations
45 - F4.3 Discharge capacity for incompressible fluids
47 - APPENDIX G - DERIVATION OF COMPRESSIBILITY FACTOR
47 - G1 SCOPE
47 - G2 EQUATION
49 - APPENDIX H - PNEUMATIC PRESSURE TESTING SAFETY REQUIREMENTS

Sets out the criteria for the design, construction and testing of safety valves, liquid relief valves, liquid level gauges, blowdown valves and other fittings for use on boilers and unfired pressure vessels and their associated piping. It does not cover the selection, operation or application of valves and fittings, as these are covered in the Standard applicable to the equipment to which the valves and fittings are to be connected. This Standard now aligns with BS 5154 in terms of valve body dimensions. This alignment will overcome the problem of differing valve body thicknesses evident in previous editions and will add to safety in the selection of correctly sized safety valves.

This Standard specifies requirements for the design, construction and testing of safety valves, liquid relief valves, liquid level gauges, blowdown valve, and other fittings for use on boilers and unfired pressure vessels, and their associated piping.It does not deal with the selection, operation, or application of valves and fittings, as these are dealt with in the Standard applying to the equipment to which the valves and fittings are to be connected, e.g. AS 1210, nor does it include requirements relating to safety fittings of a class or kind that are already the subject of a relevant Standard, e.g. -(a) Bourdon tube pressure and vacuum gauges . . . . . . . . . AS 1349;(b) bursting discs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AS 1358;(c) fusible plugs for boilers . . . . . . . . . . . . . . . . . . . . . . . . . . . . AS 1732; and(d) bursting discs and bursting disc devices . . . . . . . . . . . . .ISO 6718.

First published as AS B190-1964.
Revised and redesignated AS 1271-1973.
Second edition 1982.
Third edition 1990.
Fourth edition 1997.