MESC SPE 77-306

PRODUCTION TESTING OF VALVES IN LOW TEMPERATURE SERVICES
1. INTRODUCTION
1.1 SCOPE
1.1.1 (1) This specification covers the procedures for production testing of gate, globe, check,
ball and butterfly on/off valves and control valves used in a low temperature service
range from minus 30 ºC down to minus 196 ºC.
1.1.2 This specification shall apply in addition to the applicable MESC buying descriptions
and the referenced external standards.
1.1.3 This specification is a supplement to BS 6364 and EN 1626.
1.1.4 Clauses of BS 6364 and EN 1626 which are not amended by this specification
shall remain valid as written.
1.1.5 The numbers in brackets at the section headings refer to the relevant sections in
BS 6364.
1.1.6 Type approval testing of valves which are not yet accepted by Shell Global Solutions
International (Shell-GSI), and therefore not listed in the Shell-GSI Technical Accepted
Manufacturers And Products (TAMAP) database, shall comply with the requirements
of specification T-2.253.730.
1.1.7 Non-operable valves
Where "non-operable" is stated on the MESC buying description this means that the valve shall not be operated at service temperatures below zero degrees Celsius. These “non-operable” valves are only subject to a shell test at both ambient and low temperature conditions (see section 3.3.6.2).
2. REFERENCES
In this specification, reference is made to the following publications:
NOTE: Unless specifically designated by date, the latest edition of each publication shall be used,
together with any amendments/supplements/revisions thereto.
API 598 (8th
edition, May-
2004)
Valve inspection and testing – downstream segment
ASME B 16.34 Valves - flanged, threaded and welding ends.
BS 6364 Specification for valves for cryogenic service.
EN 1626 Cryogenic vessels – valves for cryogenic service.
EN 12300 Cryogenic vessels – cleanliness for cryogenic service.
IEC 60534-4 Industrial process control valves, part 4 inspection and routine
testing.
ISO 5208 Industrial valves – pressure testing of valves.
EN-ISO 6708 Pipe work components – Definition and selection of DN
(nominal size).
and type approval testing for on/off
specification
T-2.253.730 Procedure,
valves and control valves in low temperature (cryogenic)
services.
SPE 77/312 Fugitive emission leak detection of valves.
3. AMENDMENTS TO BS 6364 AND EN 1626.
3.1 (1) GENERAL INFORMATION AND PRE-REQUISITES
3.1.1. The valves on an order shall be separated into inspection lots, as defined in
SPE 77/302 section 4.2.1.
3.1.2 Valves to be tested shall be selected at random from the total lot.
3.1.3 The total number of samples shall be 10%, with a minimum of one per valve type,
style, size and pressure class rating.
3.1.3.1 In order to grant the manufacturer a waiver for performing production tests on
ordered valves he shall confirm that:
- he provides the client production test report(s) of at random selected
identical valve(s) which passed this test and are used for the same design
conditions.
- the accepted identical production test report(s) are not older than 2 years and
shall be part of the technical dossier.
- Documentary evidence shall be included in the technical dossier and remain with
the manufacturer.
3.1.4 The seat leakage of bi-directional valves shall be tested in both directions.
3.1.5 Valves with a preferred high pressure side (as marked on the body) shall be tested
in that preferred side.
3.1.6 Upstream-sealing valves, such as trunnion mounted ball valves shall be seat tested
on the upstream seat.
3.2 (A2) PREPARATIONS PRIOR TO PRODUCTION TESTING
facility
3.2.1 Testing
3.2.1.1 The valve shall be tested at the manufacturer's own test facilities or independent
testing facility.
3.2.1.2 Shell-GSI accepted valve manufacturers, listed in the TAMAP database, with an
inspection department independent from their production and low
temperature/cryogenic testing sections, are allowed to carry out the
SPE 77/306 production testing without the need of witnessing by an independent
inspection authority or Principal’s representative.
In all other cases:
The whole test shall be witnessed by an independent inspection authority or the
Principal’s representative.
3.2.1.3 All contacts, concerning the test arrangements shall take place directly between the
manufacturer and the testing facility/institute.
3.2.1.4 The manufacturer shall supply the testing facility/institute all relevant documents.
3.2.2 (A4) Valve production test record/certificate
3.2.2.1 During the test all observations, data and results shall be recorded in
sequence with dates and time and may be supported by photographs.
3.2.2.2 The test results and documents shall be compiled and filed by the manufacturer for
reference.
3.2.2.3 An example of a valve production test record/certificate is shown in appendix C. 3.2.3 ACCEPTANCE
REQUIREMENTS.
3.2.3.1 A lot shall be accepted if all the samples of the lot meet the specified acceptance
criteria.
3.2.3.2 If a valve fails any of the test requirements the valve shall be rejected, the cause of
the failure shall be investigated and a detailed valve component inspection is
mandatory.
3.2.3.3 In that case the valve shall be disassembled and valve parts, i.e. seats, seals,
gaskets, shall be checked for excessive wear and/or permanent deformation.
3.2.3.4 Re-testing at the specified temperature is mandatory for those valves where the measured-forces/torque during the operational test or seat test exceeds the specified limit.
3.2.3.5 When a re-test is needed the test report shall be submitted to the Principal.
3.2.3.6 In case any of the tested valves fails to meet the acceptance criteria additional
valves (the same size and pressure class) shall be tested and/or the repaired valve
shall then be re-tested.
3.2.3.7 If these samples meet the acceptance criteria, the lot shall be accepted with
exception of the initially rejected items.
3.2.3.8 If any of the additionally inspected samples fails to meet the acceptance criteria,
then 100% of the lot shall be inspected or, at the principal’s discretion, the entire lot
shall be rejected.
3.2.3.9 The re-test shall take place at the same testing facility where the previous test was
carried out.
3.2.3.10 If the test equipment fails or a shortage of gas (bottle/supply) occurs, the test shall
be aborted and the valve shall be submitted to a re-test.
3.2.4 Test rig, valve connections and supports
3.2.
4.1 (fig. 2) A schematic of a low temperature test rig is shown in Appendices B1 and B2.
3.2.
4.2 The valve and the tank shall be strong enough to withstand all forces exerted
during handling of the valve.
3.2.
4.3 The test rig shall be capable for testing the valve in both directions.
3.2.
4.4 Brackets to support the valve in the test rig shall be fixed to the valve end covers or
alternatively clamped to the body.
3.2.
4.5 There shall be no supports mounted to the stem/bonnet extension of the valve.
3.2.
4.6 The valve to be tested shall be flanged or wafer (lug) type.
3.2.
4.7 The valve ends shall be equipped with suitable end covers, capable for testing in
both directions.
3.2.
4.8 Both blind flange covers shall be provided with a pressure/vent connection and a
thermocouple connection for the closure member of the valve.
3.2.
4.9 The gaskets for the valve end blind flanges shall be spiral wound with ASTM A240
type 316(L) windings, inner and centring ring and graphite filler.
3.2.
4.10 If the valve is of the wafer(lug) type design, then the valve end connectors shall be
modified (by the manufacturer) accordingly, to accommodate this type of valve. 3.2.4.11 Deviations and/or other testing systems are subject to approval by the Principal.
3.2.5 (A
3.1.3)
Selection of the coolant medium
Service and test temperature: Type of coolant medium:
from -30 ºC down to -49 ºC alcohol with ice, liquid nitrogen or nitrogen gas
from -50 ºC down to -196 ºC liquid nitrogen with or without alcohol, or
nitrogen gas.
Deviations are subject to approval by the Principal.
3.2.6 Selection of the leak test medium
3.2.6.1 The leak test medium may be:
- helium
- pure nitrogen or
- 99% nitrogen mixed with 1% helium (used as a trace for leak detection purposes) 3.2.6.2 For tests at or close to the temperature of minus 196 ºC, only helium shall be used.
3.2.6.3 Pure nitrogen is only acceptable for seat testing if agreed by the Principal.
3.2.6.4 The test medium shall be certified before commencement of testing.
3.2.6.5 Attention is drawn to the hazardous nature of pneumatic testing.
3.2.7 Test instruments and equipment
3.2.7.1 Suitable temperature recording equipment and thermocouple connections shall be
used for monitoring the temperature throughout the test.
3.2.7.2 To measure the actual pressures both a pressure recorder and/or a pressure
gauge (with a valid calibration date) can be used.
The scale of the test pressure gauges shall not exceed twice the range of maximum
test pressure.
Note: All digital indicators shall have full scale reading.
3.2.7.3 The leakage through the test valve shall be measured by means of one of the
following devices:
- measuring cylinder in water tank
- gas flow meter soap film type
- gas flow meter (interconnected to a computer system with screen display)
- rota-meter type flow meter for high leakage rates and large valve sizes.
3.2.7.4 Fugitive volatile emissions from the stuffing box, body/bonnet and cover
connections of the valve shall be detected by means of a mass spectrometer leak
detector and sample probe as listed in SPE 77/312 section 8.4.
3.2.7.5 All measuring equipment and instruments shall have a system calibration certificate,
issued not earlier than 6 months prior to the test.
3.3 (A3) TESTING
3.3.1 General
3.3.1.1 The valve shall be visually inspected for any damage and defects.
3.3.1.2 The valve and test equipment/system shall be dry thoroughly cleaned, degreased
and dust and oil-free.
3.3.1.3 Prior to commencement of the tests the valve(s) shall be unpainted and without
internal protective coating.
3.3.1.4 If a protective coating must be removed, the valve shall be disassembled and the
valve body and internals shall be thoroughly cleaned and degreased with inhibited
methylene-chloride or tri-chlor-ethylene.
3.3.1.5 Re-assembly of the valve(s) shall be carried out at a clean location.
3.3.1.6 After re-assembly the valve shall be re-qualified to the requirements of the
applicable design standard and specification.
3.3.1.7 The tests shall be carried out in the sequence as stated in BS 6364, EN 1626
section 5.2.4 and appendix C of this specification.
3.3.1.8 The tests shall be consecutive with a minimum in delay.
3.3.1.9 Throughout the test the temperatures shall be measured and recorded of the
following measuring points:
- coolant
- valve body (outside)
- stuffing box or stem packing area (outside)
- as near as possible to the closure member (i.e. disc, wedge or ball)
Also the room temperature shall be recorded.
3.3.2 Operation of the valve (open and close)
3.3.2.1 The time to open and close wrench-manual operated valves, hand wheel and gear-
operated valves shall be the shortest possible time specified by the valve
manufacturer or Principal.
3.3.2.2 The actual force’s and torque’s (BTO, RT, ETO, BTC and ETC) applied at the valve
operator, during the maximum rated body differential test pressures for the design
temperature range, as defined in ASME B16.34, shall not exceed:
- the torque values as per the applicable design standard/specification and
- a maximum operating force of 350 N at the lower design temperature.
3.3.2.3 The opening force, closing force and torque of each first operation shall be
measured and recorded.
3.3.2.4 During the valve seat test, after the first and last pressure increment the valve shall
be fully opened and closed five times.
3.3.2.5 Manually operated valves shall be operated without the use of spanners (wheel
keys) or any other extension devices.
3.3.2.6 The use of air-tool equipment for operation of the valve during this test is
acceptable.
3.3.2.7 For motor operated valves (with a gearbox or actuator), provisions shall be made to
monitor the performance of this operating device as such that an indirect
measurement of the torque requirements is achieved.
3.3.2.8 After the seat test the closure member of check valves shall be checked
against jamming in the close position by internal pressure difference.
pressures
3.3.3 Test
Body pressure test: The objective of a body pressure test is to prove the
quality of the materials used and the construction of the pressure equipment
before it enters or re-enters service.
Seat pressure test: The objective of a seat pressure test is to prove the
tightness of the valve seat(s) against leakage.
Back seat test: The objective of the backseat test is to prove the tightness of
the backseat against leakage to the stuffing box area.
3.3.3.1 The maximum body test pressure and seat test pressure shall comply with the
applicable valve design code specified in the purchase order MESC description. 3.3.3.2 Valve body materials are listed in material groups in ASME B16.34 table 1.
3.3.3.3 For metal seated valves, per material group, the nominal pressure/temperature
rating (PN) at the applicable test temperature shall be selected from ASME B16.34
table 2.
3.3.3.4 The shell (hydrostatic and pneumatic) test pressures, the closure (seat) high-
and low test pressures and backseat test pressure shall comply with the
values specified in API 598 sections 3.3, 3.4, 3.5 and tables 2 and 3.
3.3.3.5 When the valve size and/or rating would seriously hamper the practicality of the test
a reduced test pressure may be considered, however this is subject to approval by
the Principal.
3.3.3.6 (A3.1.
4.d) The test pressure shall preferably be raised in 3 equal increments minimum.
However, the manufacturer may decide to perform the test in 4 or 5 equal
increments.
temperature
3.3.4 (A1) Test
3.3.
4.1 The valve temperature range (service duty) of the valve is stated in the MESC
buying description.
3.3.
4.2 The valve test temperature difference between valve body and closure member
shall not deviate more than 5% from the lower design temperature or 5 ºC,
whichever is the greater.
3.3.
4.3 Tests executed on valves with a lower design temperature of minus 196 ºC may
commence when the body has reached minus 190 ºC.
3.3.
4.4 The actual test temperature for valves with impact test qualified carbon steels (LCB)
shall not be lower than the qualification design temperature with the valve under
working pressure, i.e.: - 50 ºC.
3.3.5 (A3.1.3)
Cooling-down
3.3.5.1 During the cooling down period the temperature shall be measured and recorded.
Manually recordings at least every 10 minutes. The records may be provided on
separate sheets.
3.3.5.2 The valve shall be installed in the test tank and cooled down with the stem in the
vertical (upright) position.
3.3.5.3 In case of immersed in the coolant the top of the valve body/bonnet shall be just
covered.
3.3.5.4 The stem seal(s) and/or stuffing box shall be above the maximum cold fluid level in
the tank.
3.3.5.5 To prevent the formation of moisture in the valve during the cooling operation, a
minimum pressure purge of 0.5 barg helium or nitrogen gas through the valve shall
be maintained with the valve in half open position.
3.3.5.6 Soft-seated valves shall be kept in the fully open position and shall only be operated
(closed and opened) regularly, when cavity purging is required.
3.3.5.7 The test may commence when the valve body and the internals have reached the
specified test temperature (see section 3.3.4).The purge shall be switched off.
Stabilise the temperature for 5 minutes.
3.3.5.8 The valve shall be then in the fully open position.
The complete system including the test valve/cavity shall be de-pressurised.
3.3.6 Tests at specified low temperature
test - (internal leakage)
3.3.6.1 Seat
3.3.6.1.1 The test valve shall be in the closed position and subjected to the test pressure in 3
equal increments minimum. (ref. 3.3.3).
3.3.6.1.2 A minimum closure force shall be applied and recorded to obtain a leakage less
than the maximum allowable leakage specified.
3.3.6.1.3 The down stream side of the valve shall be de-pressurised at the beginning of the
test and after each pressure increment.
3.3.6.1.4 After the last increment the test pressure shall be maintained.
3.3.6.1.5 After the pressure is stabilised, the leakage through the valve shall be recorded at
each pressure increment during a period of three minutes.
3.3.6.1.6 For the allowable leakage rates see appendix A.
test (external leakage of body/bonnet or body/cover)
3.3.6.2 Shell
3.3.6.2.1 The valve shall be outside the test tank, set in half open position and subjected to
the test pressure. Soft seated ball valves however shall be set in the fully open
position (to prevent possible damage of the soft seats) and subjected to the test
pressure.
3.3.6.2.2 The following specific components shall be checked for leakage and/or porosity:
- body/bonnet joint or body/cover flanges.
- stem extension, (connections)
- stuffing box-stem seal and gland (follower)
- around the end flange(s) or the valve connectors (for non end-flanged valves)
- tubing connections of test rig
3.3.6.2.3 The leakage of the test piping or tubing is excluded from this test.
3.3.6.2.4 Check for leakage during a minimum period of 5 minutes.
3.3.6.2.5 The measured body leakage rate for valves, tested at ambient and the specified low
temperature, shall be zero. Any fugitive emissions shall be less than the values
specified in the purchase order, i.e. the MESC buying description and SPE 77/312.
3.3.6.2.6 All data shall be recorded.
test (at maximum pressure)
3.3.7 Operational
3.3.7.1 The in the test rig installed valve shall be opened and the maximum allowable rated
seat test pressure shall be applied from the preferred side (Ref. 3.3.3).
3.3.7.2 Set the closure member of the test valve in the closed position.
3.3.7.3 Release the test pressure at the downstream side of the valve to atmospheric
pressure.
3.3.7.4 The test pressure at the pressurised side and the cavity shall be maintained.
3.3.7.5 The pressure shall be stable for one minute at the beginning of the first operation of
the valve.
3.3.7.6 Possible stem- and/or body-bonnet leakages shall be checked prior operation
testing.
3.3.7.7 (A3.1.
4.c) The valve shall be operated (open and immediately closed) 5 full strokes.
3.3.7.8 The torque (force)s of the (open and close) operation of the valve shall be recorded.
3.3.7.9 The maximum allowable force applied at the wrench or hand wheel is 350 N.
3.3.7.10 After the operational test, the complete system and test valve shall be fully de-
pressurised (including valve cavity).
3.3.8 Warming-up
completion of the leakage tests:
3.3.8.1 After
- the valve shall be in the half open position, however
- soft seated ball valves shall be set in the fully open position (to prevent
possible damage of the soft seats),
de-pressurised (including any valve cavity) and be kept outside the test tank for
warming-up to ambient temperature.
3.3.8.2 A forced warming-up, e.g. using hot-air blowers or heaters, is not allowed.
However, air circulation around the valve at room temperature caused by fans is
acceptable.
inspection
3.3.9 Final
3.3.9.1 When the valve is at room temperature the valve and internals shall be cleaned and
dried. The cleanliness requirements shall comply with EN 12300.
3.3.9.2 End connectors and other test rig equipment shall be removed from the valve.
3.3.9.3 After successful completion of all tests (see 3.2.3.2) the valve need not be
disassembled for component inspection but shall be visually inspected only.
APPENDIX A
MAXIMUM ALLOWABLE LEAKAGE RATES FOR ON/OFF VALVES (see notes)
Shell (body), bonnet and stem seals leakage tests
Depending on the media and service application, the actual leakage rates for valves, tested at both ambient and the specified low temperature conditions, shall be less than the values specified in SPE 77/312, section 6.
The maximum allowable body leakage is zero (i.e. in compliance with ISO 5208, rate A).
Seat leakage:
The allowable seat leakage (both seats), shall be in accordance with ISO 5208 or BS 6364 appendix A ., pneumatic tested at ambient temperature, specified low pressure and rated seat test pressure:
Valve seat type: Valve type:
Resilient (soft) seated: Metal/soft seated (fire safe): Metal seated:
Ball, gate, globe
ISO 5208, rate A
0 mm³/s*DN
(Note 2)
N.A.
ISO 5208, rate B
(0.3 mm³/s*DN)
(Note 2)
Butterfly ISO 5208, rate A ISO 5208, rate A
ISO 5208, rate A
or rate B
(Note 3)
(8.3.2)
Check (i.e.: swing, tilting disc, piston and dual plate types).
ISO 5208, rate B
(Notes 2 and 4)
N.A.
ISO 5208, rate D 30 mm³/s*DN
(Notes 2 and 4)
(A.3)
Allowable seat leakage (both seats), tested with helium at specified low temperature,
specified low pressure and rated seat test pressure:
Maximum allowable leakage rates for valves with seat types:
Valve type:
resilient (soft) seated: fire safe = metal/soft seated: metal seated:
(A.3.1.4) gate, globe, ball and
butterfly (A.3.1.4.d) 33 mm³/s*DN (note 2) 67 mm³/s*DN (note 2) 100 mm³/s*DN (note 2)
(A.3.2.4) check, i.e.: swing,
tilting disc, piston types and dual plate types. (A.3.2.4.d)
67 mm³/s*DN (notes 2 and 4)
N.A.
BS 6364 appendix A clause A.3.2.4 200 mm³/s*DN
(Notes 2 and 4)
Notes:
1. For control valves: In general the maximum allowable seat leakage shall comply with IEC 60534-4
table III, i.e.: 1 * 10E-3 rated valve capacity.
For cryogenic applications (see T 2.253.730 section 5.2.4):
class A: maximum leakage rate: 5 * 10E-6 rated valve capacity,
class B: maximum leakage rate: 1 * 10E-4 rated valve capacity.
2. The valve nominal size DN is measured in mm of bore, in accordance with EN-ISO 6708.
The nominal bore or reduced (nominal) bore as per BS 6364 appendix A.
3. The maximum allowable seat leakage rate for butterfly valves in the non preferred flow direction shall
comply with SPE 77/134 section 6.1.7.
4. The purpose of a check valve is to prevent unwanted reverse flow in circumstances of process change
or system failure. Therefore check valves are not intended to be isolation valves and as such does not specify very tight seat leak rates.
APPENDIX - B1
S c h e m a t i c o f T e s t -R i g A r r a n g e m e n t f o r ‘D u a l P l a t e C h e c k V a l v e ’ T y p e A p p r o v a l T e s t s
Appendix-B2
APPENDIX C PAGE 1 OF 4 VALVE PRODUCTION TEST RECORD / CERTIFICATE
Valve make: Valve type:
Valve style no: Valve figure no:
Valve sealing 2): Uni / bi directional Nominal size:
Class rating: Temperature range:
Design standard: MESC number:
Body material: Seat material:
Date of testing:
Seat
facing
material:
Valve is tested in
SPE 77/306 Report reference no:
accordance with:
Principal: Purchase order no:
Test results:
Actual
limit:
Testing at ambient temperature: Specified
measured:
Actual ambient temperature: N.A. ºC
1st operational test [3.3.7] 5 full strokes:
Operational force to open and close: 350/350 N / N
diameter hand wheel / wrench m m
seat test in preferred flow direction at
maximum differential pressure barg barg
leakage rate cm³/5 min cm³/5 min leak test medium: Nitrogen/helium
a)
seat test in non-preferred flow direction at
maximum differential pressure barg barg
leakage rate cm³/5 min cm³/5 min leak test medium: Nitrogen/helium
a)
test
shell
pressure barg barg maximum
leakage rate zero cm³/5 min cm³/5 min leak test medium: Helium
2nd operational test [3.3.7] 5 full strokes:
Operational force to open and close: 350/350 N / N
diameter hand wheel / wrench m m
APPENDIX C PAGE 2 OF 4 VALVE PRODUCTION TEST RECORD / CERTIFICATE
Cooling down [3.3.5]: Specified limit: Actual
measured: Testing at low temperature [3.3.6]:
3rd operational test [3.3.7]:
Specified and actual low temperature: ºC ºC
seat test in preferred flow direction
[3.3.6.1]:
leak test medium: Nitrogen/helium
a)
1st increment (low differential pressure) barg barg
leakage rate cm³/5 min cm³/5 min 2nd increment (medium diff. Pressure) barg barg
leakage rate cm³/5 min cm³/5 min
barg barg 3rd increment (max. differential
pressure)
leakage rate cm³/5 min cm³/5 min
Cooling down [3.3.5]: Specified limit: Actual
measured: Testing at low temperature [3.3.6]:
3rd operational test [3.3.7]:
Specified and actual low temperature: ºC ºC
seat test in non-preferred flow direction
[3.3.6.1]:
leak test medium: Nitrogen/helium
a)
1st increment (low differential pressure) barg barg
leakage rate cm³/5 min cm³/5 min 2nd increment (medium diff. pressure) barg barg
leakage rate cm³/5 min cm³/5 min
barg barg 3rd increment (max. differential
pressure)
leakage rate cm³/5 min cm³/5 min shell test [3.3.6.2]:
pressure barg barg maximum
leakage rate zero cm³/5 min cm³/5 min leak test medium: Helium
4th operational test [3.3.7] 5 full strokes:
Operational force to open and close: 350/350 N / N
diameter hand wheel/wrench m m
APPENDIX C PAGE 3 OF 4 VALVE PRODUCTION TEST RECORD / CERTIFICATE
Warming up [3.3.8]: Specified limit: Actual
measured: Actual ambient temperature: N.A. ºC
Seat test in preferred flow direction
leak test medium: Nitrogen/helium a)
maximum differential pressure barg barg leakage rate cm³/5 min cm³/5 min Seat test in non-preferred flow direction
leak test medium: Nitrogen/helium a)
maximum differential pressure barg barg leakage rate cm³/5 min cm³/5 min REMARK: a) Delete what is not applicable
APPENDIX C PAGE 4 OF 4 VALVE PRODUCTION TEST RECORD / CERTIFICATE
inspection/examination [3.3 and 3.3.9]:
Visual
Observations and findings:
Valve disassembled: yes/no
Condition of components:
Any other comments and/or additional test data:
by: Signature:
Tested/reported
Date:
authority: Signature:
Inspection
Date:
Witnessed
by: Signature:
Date:
REMARK: 1) The numbers between brackets refer to the relevant sections in this specification.。