1、BSI Standards PublicationBS 746:2014Specification for gas meterunions and adaptorsPublishing and copyright informationThe BSI copyright notice displayed in this document indicates when the documentwas last issued. The British Standards Institution 2014Published by BSI Standards Limited 2014ISBN 978
2、0 580 74892 9ICS 21.060.01The following BSI references relate to the work on this document:Committee reference GSE/25Draft for comment 12/30243876 DCPublication historyFirst published December 1937Second edition February 1958Third edition January 1967Fourth edition April 1987Fifth edition May 2005Si
3、xth (present) edition November 2014Amendments issued since publicationDate Text affectedBS 746:2014 BRITISH STANDARDContentsForeword ii1 Scope 12 Normative references 13 Terms and definitions 24 Materials 25 Dimensions 56 Machined surfaces 57 Screw threads 58 Strength of nuts and female adaptor ends
4、 59 Finish 610 Marking 6Bibliography 15List of figuresFigure 1 Basic Whitworth form 5List of tablesTable 1 Initial and release torques 3Table2Torque for strength test 6Table 3 Boss dimensions 7Table 4 Nut dimensions 8Table 5 Liner dimensions 9Table 6 Reducing adaptor dimensions 10Table 7 Increasing
5、adaptor dimensions 11Table 8 Union washer dimensions 12Table 9 Adaptor washer dimensions 12Table 10 Sealing disc dimensions 13Table 11 External thread dimensions 14Table 12 Internal thread dimensions 14Summary of pagesThis document comprises a front cover, an inside front cover, pages i to ii,pages
6、1 to 16, an inside back cover and a back cover.BRITISH STANDARD BS 746:2014 The British Standards Institution 2014 iForewordPublishing informationThis British Standard is published by BSI Standards Limited, under licence fromThe British Standards Institution, and came into effect on 30 November 2014
7、. Itwas prepared by Technical Committee GSE/25, Gas meters. A list of organizationsrepresented on this committee can be obtained on request to its secretary.SupersessionBS 746:2014 supersedes BS 746:2005+A1:2009, which is withdrawn.Relationship with other publicationsThis standard specifies fittings
8、 to be used in conjunction with gas meters such asthose specified by BS EN 1359 and BS EN 14236.Information about this documentThis is a full revision of the standard, and introduces the following principalchanges. Dimensional changes have been made to ensure that the flat parts of thenuts engage di
9、rectly on the flat parts of the liners such that even pressure isapplied to the surfaces of the washers. The properties of the sealing washer have been redefined. Additional tests for fittings and washer performance have been added. Hexagonal nuts are now permitted as an alternative to octagonal nut
10、s.This document may be used in the procurement of fittings.Presentational conventionsThe provisions of this standard are presented in roman (i.e. upright) type. Itsrequirements are expressed in sentences in which the principal auxiliary verb is“shall”.Commentary, explanation and general informative
11、material is presented insmaller italic type, and does not constitute a normative element.Contractual and legal considerationsThis publication does not purport to include all the necessary provisions of acontract. Users are responsible for its correct application.Compliance with a British Standard ca
12、nnot confer immunity from legalobligations.BRITISH STANDARDBS 746:2014ii The British Standards Institution 20141 ScopeThis British Standard specifies requirements and test methods for unions andadaptors for the installation of low pressure gas meters. It is applicable tounions and adaptors for gas m
13、eters for use with 1st, 2nd and 3rd family gases attemperatures between 20 C and +60 C, up to a maximum operating pressureof 75 mbar1)and a maximum incidental pressure of 200 mbar. The gas tightnessof the gas meter unions and adaptors is also specified.NOTE The tests specified in this standard are t
14、ype tests, except for that specifiedin 4.2.3.2 Normative referencesThe following referenced documents are indispensable for the application ofthis document. For dated references, only the edition cited applies. For undatedreferences, the latest edition of the referenced document (including anyamendm
15、ents) applies.BS 1936-1, Undercuts and runouts for screw threads Part 1: Inch screw threadsBS 7371-6, Coatings on metal fasteners Part 6: Specification for hot dippedgalvanized coatingsBS EN 549, Specification for rubber materials for gas appliances and gasequipmentBS EN 1562, Founding Malleable cas
16、t ironsBS EN 1652, Copper and copper alloys Plate, sheet, strip and circles for generalpurposesBS EN 1976, Copper and copper alloys Cast unwrought copper productsBS EN 1982, Copper and copper alloys Ingots and castingsBS EN 10088-3:2005, Stainless steels Part 3: Technical delivery conditions forsemi
17、-finished products, bars, rods, wire, sections and bright products ofcorrosion resisting steels for general purposesBS EN 10242, Threaded pipe fittings in malleable cast ironBS EN 12164, Copper and copper alloys Rod for free machining purposesBS EN 12165, Copper and copper alloys Wrought and unwroug
18、ht forging stockBS EN 12167, Copper and copper alloys Profiles and rectangular bar forgeneral purposesBS EN 12168, Copper and copper alloys Hollow rod for free machiningpurposesBS EN 12329:2000, Corrosion protection of metals Electrodeposited coatings ofzinc with supplementary treatment on iron or s
19、teelBS EN 12420, Copper and copper alloys ForgingsBS EN ISO 27830, Metallic and other inorganic coatings Guidelines forspecifying metallic and inorganic coatingsPD 970, Wrought steels for mechanical and allied engineering purposes Requirements for carbon, carbon manganese and alloy hot worked or col
20、dfinished steels1)1 bar = 105 N/m2 = 100 kPa.BRITISH STANDARD BS 746:2014 The British Standards Institution 2014 13 Terms and definitionsFor the purposes of this British Standard the following terms and definitionsapply.3.1 adaptormetal fitting for connecting a nut and liner to a boss of a different
21、 size3.2 apparatusconstruction of pipes, fittings, test points, etc., that is leak tight3.3 bosspart of a fitting with an external screw thread3.4 adaptor washerelastomeric seal between a boss and an adaptor3.5 linermetal fitting with a flanged end to take union washer3.6 nutmetal fitting with an in
22、ternal screw thread3.7 sealing discmetal fitting fitted between a boss and a nut, with or without a liner, designedto close off the gasway3.8 unionmetal fitting comprising a boss and a liner using a washer and nut for gastightness3.9 union washerelastomeric seal between a boss and a liner4 Materials
23、4.1 Metal fittingsMetal fittings shall be made from one of the following materials:a) brass for hot pressing, grade CW602N or CW617N to BS EN 12165 orBS EN 12420;b) brass for casting, grade CC490K, CC491K, CC750S, CC754S or CC760S toBS EN 1982;c) brass rod, grade CW602N, CW614N or CW617N to BS EN 12
24、164, BS EN 12167or BS EN 12168;d) brass sheet and strip, grade CW508L to BS EN 1652;e) copper, grade CR004A to BS EN 1976;f) malleable cast iron to BS EN 1562;g) carbon steel of any grade, with a content not exceeding 0.01% for lead,0.06% for sulfur and 0.06% for phosphorous and which is suitable fo
25、rwelding, and forming or machining, as appropriate, to PD 970; orh) austenitic stainless steel to BS EN 10088-3:2005, grades 1.4404 and 1.4541.BRITISH STANDARDBS 746:20142 The British Standards Institution 20144.2 Elastomeric washers4.2.1 GeneralElastomeric washers shall be tested in accordance with
26、 BS EN 549. Whentested in accordance with BS EN 549, the material from which elastomericwashers are made shall:a) be of a hardness 913 IRHD2);b) otherwise conform to BS EN 549, grade H3, A2.4.2.2 Leak rate at low pressure4.2.2.1 Leak rateEach size of washer (see Table 8 and Table 9) shall be tested
27、separately inaccordance with 4.2.2.2. When tested in accordance with 4.2.2.2, the totalleak rate of the assembly shall not exceed 0.2 L/h and the release torque ofany union nut shall be not less than given in Table 1.Table 1 Initial and release torquesNominal sizeinInitial torque Release torque12 34
28、 25 812514114 35 20112 45 282 100 374.2.2.2 Test method4.2.2.2.1 Select 60 washers and divide these into four groups of 15. Erect fourseparate assemblies, each:a) comprising 15 washers, nuts, liners and bosses, together with suitableapparatus that includes means of allowing the internal pressure of
29、eachassembly to be changed and measured; andb) having an internal volume not exceeding 0.035 m3.Calculate the internal volume of each assembly.4.2.2.2.2 Allow the apparatus, washers, nuts, liners and bosses to stabilize at(20 3) C for a period of 1 h. Assemble the washers, nuts, liners and bosses an
30、dtighten each nut to the applicable torque given in Table 1.2)International Rubber Hardness DegreesBRITISH STANDARD BS 746:2014 The British Standards Institution 2014 34.2.2.2.3 Subject each assembly to the following environmental conditions, asapplicable.Assembly 1Leave at room temperature of (20 3
31、) C for a period of not less than 4 h.Assembly 2Leave at room temperature of (20 3) C for a period of 1 h, then place theassembly in an environmental chamber at a temperature of (20 3) C andleave for a period of not less than 4 h. Remove the assembly from theenvironmental chamber and leave the assem
32、bly at room temperature for aperiod of 2 h.Assembly 3Leave at room temperature of (20 3) C for a period of 1 h, then place theassembly in an environmental chamber at a temperature of (60 3) C and leavefor a period of not less than 4 h. Remove the assembly from the environmentalchamber and leave the
33、assembly at room temperature of (20 3) C for a periodof2h.Assembly 4Leave at room temperature of (20 3) C for a period of 1 h then place theassembly in an environmental chamber at a temperature of (20 3) C andleave for a period of not less than 4 h. Increase the temperature within thechamber to (60
34、3) C, and once a temperature of (60 3) C is reached maintainthe temperature for a period of not less than 4 h. Remove the assembly fromthe environmental chamber; leave the assembly at room temperature of(20 3) C for a period of 2 h.NOTE If any of the groups are split into subgroups, due for example
35、to theenvironmental chamber being unable to accommodate 15 samples, it is necessary tobe able to show that the test conditions were the same for each subgroup.4.2.2.2.4 After each assembly has undergone the environmental conditioningspecified in 4.2.2.2.3, set the pressure in the assembly to 75 mbar
36、. Isolate thepressure supply, then observe a 1 min temperature stabilization. Take thepressure (P1) within the assembly and observe a test period of 2 min. Followingthis, take a second pressure reading (P2). Calculate the rate of leakage duringthe test period using the total volume of the assembly u
37、nder test and the twopressures P1 and P2. The gauge used shall be a digital pressure gauge with aresolution of 2 dcp.NOTE 1 When undertaking the gas tightness test, care has to be taken not to affectthe gas tightness of the assembly, e.g. avoid tightening against it or otherwiseclamping the joint.NO
38、TE 2 It is not necessary to test all groups simultaneously, only that 60 samples betested in four groups.4.2.3 One-off test for complete assembly with new washers4.2.3.1 Each size of washer (see Table 8 and Table 9) shall be subjectedseparately, as part of a complete assembly, to the gas tightness t
39、est in 4.2.3.2.When tested in accordance with 4.2.3.2, no air bubbles shall be released fromthe assembly.4.2.3.2 Select five new washers of each size and assemble the washers, nuts,liners and bosses. Tighten each nut to the applicable torque given in Table 1.Pressurize the assembly to 350 mbar and s
40、eal off the ends. Immerse theassembly in a water bath which is at ambient temperature and with a depth notexceeding 300 mm. Observe for a period of 30 s after any external trapped airhas been dispersed.BRITISH STANDARDBS 746:20144 The British Standards Institution 20145 Dimensions5.1 GeneralFittings
41、 shall conform to the appropriate dimensions specified in Table 3 toTable 10, as applicable.NOTE Reference numbers have been added to Table 4 and Table 6 to Table 10 toassist the ordering and purchase of fittings.5.2 UndercutsThe thread undercuts shall be Grade 1, Form A, Width 2p in accordance with
42、BS 1936-1, except that undercut radius shall be 0.5 mm.6 Machined surfacesThe machined surface of a fitting shall have:a) a concentricity tolerance on all threads and diameters of 0.4 mm; andb) a surface roughness of not more than 1.6 m on the sealing faces.7 Screw threadsScrew threads shall conform
43、 to the dimensions given in Table 11 and Table 12,and shall be of basic Whitworth form as illustrated in Figure 1.Figure 1 Basic Whitworth formKeyP PitchH 0.960491 Pr 0.137329 PNOTE The Whitworth form of threads is one in which the angle between the flanks,measured in the axial plane, is 55; one-six
44、th of the sharp triangle is truncated at topand bottom, the threads being rounded equally at crests and roots.8 Strength of nuts and female adaptor ends8.1 Nuts and adaptors shall be tested in accordance with 8.2. When tested inaccordance with 8.2, nuts and the female ends of adaptors shall not frac
45、ture.8.2 Screw a nut fitted with a liner or adaptor, but without the washer, onto asuitable boss component and tighten to the appropriate torque given in Table 2.BRITISH STANDARD BS 746:2014 The British Standards Institution 2014 5Table 2 Torque for strength testNominal sizeinTorqueNm12 12534 1501 1
46、50114 175112 2002 2009 FinishMetal fittings shall be clean and free from scale.Metal components, excluding meter bosses, conforming to 4.1f) and 4.1g) shallbe protected from corrosion in accordance with a) and b), as applicable. Theprotective finish shall be such as to not affect the dimensional con
47、formity ofthreads in Table 11 and Table 12 or the efficacy of sealing surfaces (as specifiedin Clause 10).a) Where a hot dipped zinc corrosion protection coating is applied tomalleable cast iron conforming to 4.1f), this shall conform to BS EN 10242 orBS 7371-6.b) Where an electroplated zinc and chr
48、omate passivated corrosion protectioncoating is applied to carbon steel conforming to 4.1g), the coatingdesignation shall conform to BS EN 12329 and, as a minimum, be suitablefor service condition 3, as defined in BS EN ISO 27830, or as agreed with thepurchaser. The chromate conversion coating shall
49、 be trivalent, rather thanhexavalent, and conform to the corrosion resistance test requirements forthe corresponding chromate conversion code in BS EN 12329:2000, Table 2.NOTE Requirements for the corrosion protection of meter bosses are given ingas meter standards, e.g. BS EN 1359 and BS EN 14236.10 MarkingThe nut, union, liner, boss and adaptor shall be marked with the followinginformation.a) The name, trade mark or other means of identification of the manufacturer
