BS 2654 Vertical Steel Welded Non Refrigerated Storage Tanks

 

BSI BS*E b59

8 7 W 3 6 2 4 b b 70 3 4 3 3 2 3

7

m

B S 2654 : 1989 UDC 665.7.004 : 621.642.3-1 1 1 I : 621.772.46 : 669.14.018.62 : 621.791.75.053.6

(Q British Standards Institution. No part of t h i s publication

may b e phot photoc oc oDi oDi e ed d or ot h ed s e r eDr eDr oduced oduced wi thout the orior Dermission n wr i ti na of B S I

British Standard Specification for  

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Manufacture of vertical steelwelded w elded non-refrigerated storage tanks ith butt-we bu tt-we lde lded d shel shells for the petroleum industry

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Fabrication des réservoirs de stockage verticaux non refrigérés en acier à enveloppe soudée bout à bout pour 'industrie de pétrole - Spécifications Herstellung stehender ungekühlter Lagertanks au aus s Stahl m i t stumpgeschweißtem Mantel für die Erdölindustrie

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B S 2654: 989

Foreword

prepared red und under er the direc tion of This British Standard was prepa the Pressure Vessel Standards Policy Committee and

The method specified s for determining the notch toughness required of a material in any given given thickness thickness for design temperatures down o - 10 OC based on t e s t s in which through-thickness defectsup to 10 mm long, located

a range of adequate economy inoi suitable suita ble capacit casafety, pacities iesreasonable fo r the storage stora ge of oiand l and l products. The comm committee ittee recog recognizes nizes,, howeve however, r, that this standard could be adopted with equal safety and economy by other industries and/or for the storage of other products, although althou gh purc purchas hasers ers and manufacturers may ne need ed to formul for mulate ate an and d agree agree ad additional ditional requirements necessitated by the conditions pertaining o a particular application. N O T E . Users of this British Standard are reminded that the B S I

both in ocally embrittled and post-weld heat treated material, material , ar are e required to withstand approximately four times yield point strain (see figure 1).

replaces BS 2654 : 1984 which is now withdrawn. It is desi design gned ed to provide the petroleum industry w it h tanks of

committee respon responsible sible s prepared to offer interpretations of the t e x t on request.

The require requirements ments for material selection in this standard standard ha have ve be been en ba base sed d on tthe he resu results lts of a number of notched and welded Wells Wide Plate Tests (WWP Tests) on carbon and carbon/manganese s t e e l plates, carried out a t the Welding Institute Inst itute . I n partic particular, ular, the proposal proposals s are are related to the results reported n 'Mild steel for pressure equipment subWelding g Journal, Journal, March 1964, zero temperatures', Britis h Weldin but all other known WWP t e s t data have been taken into account. They also reflect many subjective assessments of practice to date in this field as permitted by current British, American and German codes. WWP t e s t data all indicate that resi resista stanc nce e to br it tl e racture i s dependent upon the ollowing.

( a ) Notch toughness of the material. (b) P l a t e thickness. (c) Extent of crack-like defects present; t i s believed tha t i f suc such h defect defects s are are a abs bsen ent, t, b bri ritt tt le fracture wi ll not be a problem a t normal rates of loading. (d ) Degr Degree ee of local embrittlement a t tip ofpre-existing ofpre-existing defects; defec ts; i n the case of carbon and carbodmanganese steels, post-weld hea heatt treatment in the stress r e l i e v i n g range temperature i s effect effective ive in removing se seve vere re embrittlement arising as a result of welding and/or flame cutting cutt ing operations.

Scale A i s derived using hese criteria and data from WWP t e s t s for as-welded oints.

Scale B is used for determining the requirements or the hydrostatic test. Appendix A gives recommendat recommendations ions for tank foundations and appendix B gives recommendations for the design and application of insulation. This standard i s exp expres ressed sed in metric me tric uni units ts and a proposed range of standard metric diameters and capacities capacities i s given in appendix appendix C. Al l pressure pressure and vac vacuum uum values values n this t his standard standard are expressed a s gauge values. The symbols used throughout the text are as listed in appendix D. Appendix E gives recommendations for internal floating covers, appendix F gives recommendations for the design of vent venting ing sy systems stemsand appendix appe ndix G offers offer s seismic oading provisions. It has has be been en as assu sume med d in the draf d raf tin ting g of this Bri Britis tish h Standard that the execution execution of i t s provisi provisions.is ons.is entrusted to appropriately qualified and experienced people.

This edition introduces technical changes to bring the standard up-to-date but t does not reflect a fu ll revie review w of the standard, which will be undertaken in due course. Compliance Compli ance wit h a Brit British ish Standard Standard do does es not of itself confer conf er iimmunity mmunity from egal obligations.

 

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BSI B S * 2 6 5 4 8 7 m 1629bb4 0191325 O m B S 2654 : 1989

Contents

Page

Page

9.1 Roo Rooff manh manholes oles 9.12 Centering and anti a nti -ro -rotat tat ion devic device e 9.13 Seals evice 9.14 Gauging 3 9.1 5 Operation 3 10 Tank nchorage 3 10.1 General 3 10.2 Anchoragettachment 10.3 Allowable tensile stress 10.4 Holding-down bolt orstrap orstrap 10.5 Resi Resistan stance ce to t ouplift 3 Mountings 11 3 Shell manholes and shell nozzles 80 mm 11 I outside diameter (0.d.) and above 4 11.2 Shell nozzles less than 80 mm 0.d. manholesand andnozzles nozzles 11.3 Roof manholes 4 11.4 Addition Additional al loa loads ds 5 Nozzlewelding weldingdetails details 11.5 Nozzle 5 11.6 Inspec Ins pectio tion n of shellmanholesandnozzles 5 11.7 Fl Flang ange e drill ing 5 11.8 Post-weld heat heat treatment treatmen t 5 11.9 Procedure for post-weld heat treatment 5 Stairways ways and gangways gangways 11.1 O Stair 6 11.1 1 Handrailing 6 1 1.1 2 Ladders 8 connections 1 1 I 3 Earthing connections 8 clean- out doors, doors, D-type D-ty pe su sump mps s 1 1 .I4 Flush type clean-out 8 and water draw-off sumps 8 1 1 I 5 Permanent attachments 8 attachments 1 1 .I6 Temporary attachments 8 12 Insulation 8 13 Shop fabrication 8 13.1 Workmanship 8 13.2 Hard Hardtamping tamping 8 13.3 Plate edge prcparation 10 13.4 Rolling andpressing 11 13.5 Bolt holes 11 13.6 Surface preparation and painting

21 21 21 21 21 21 21 21 21 23 23 23

12 12 16 16 16 16 16

8.5 8.6 9 9.1 9.2 9.3 9.4

Internal loading Wind and vacuum vacuum loading Shell plate .arrangement Shell joints Fixed-roof Fixedroof design design Loads Type of roof Roof plating plating w it h supporting supporting st structu ructure re Roof plating without supporting structure (membrane (membr ane roofs) roofs ) Compression area Venting requirements Floating-roof design General Design requirements Stability of roof under wind load Pontoon openings

9.5 9.6 9.7 9.8 9.9 9.10

Bulkheads Movable Mova ble ladders ladders to roofs Primary roof drains Emergency drains Vents Supporting legs

19

Foreword Committees responsible

Inside fr on t co cover ver Back cover

Specification 1

2 2.1 2.2 3

3.1 3.2 3.3 3.4 4 4.1 4.2 4.3 4.4 4.5 4.6 5 5.1 5.2 5.3 5.4 5.5 5.6 5.7 6 6.1 6.2 7 7.1

 

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7.2 7.3 7.4 7.5 8 8.1 8.2 8.3 8.4

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Scope Design Des ign conditions conditio ns Design pressure Design Des ign metal temperature Information to be exchanged prior to implementing he requirements requirements of this standard and inspections by the purchaser during erectio erection n Information to be specified by the purchaser Optional and/or alternative alternative information t o be supplie supplied d by the t he purchaser Informa Info rmation tion t o be agreed agreed be betwe tween en the purchase purc haserr and the manufacture manuf acturerr Inspections by the purchase purchaserr during erection Materials Specifications Steelmaking process Chemical composition Notch Notc h duct ility Mountings Other requirements Design oadings General Dead oads Superimposed oads Contents Loads Loa ds resulti resulting ng fr from om connected piping pip ing Wind oading Seismic Seis mic loa loads ds (if applicable) Bottom Bot tom design design General Design Shelll design Shel Design stresses

COPYRIGHT 2002; British Standards Institution on ERC Specs and Standards -

16

17 17 18 18

18 19 19

19

19 20 20 20 20 5.6

23 28 28 28 28 28 28 40 40 40 41 41 41 41 41 41 41 52 52 52 52 52 52 52

13.7 13.8 13.9 14 14.1 14.2 14.3 14.4 14.5 14.6 14.7 14.8 14.9 14.10 14.11 14.12 15

Erectio n marks domestic market) Erection Erection marks marks (export (exp ort market) Packaging Si t e erection General Workmanship Tank foundation construction Rectification of damage to materials Erection of pla plates tes Shellolerances olerances Floating-roo Floati ng-rooff tolerances tolerances Manual oxygen cutting Protection of sh shell ell during erection. Erection Erect ion of fixe d rroof oof Erection Erectio n holes Final surface surface finish Welding

52 52 52 53 53 53 53 53 53 53 54 54 54 54 54 54 54

15.1 15.2 15.3 15.4 15.5

Weldingrocess Welding rocess Weldingequences Weldingequences Vertical joints Weather Weat her conditions Preheating Electrodes

54 54 54 54 55 55

7

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BSI B S * 2 6 5 4

87 W 3624667 0343326 2

m

B S 2654 1989

Page

15.7 15.8 15.9 15.1 O 15,ll 15.12 15.13 15.1 4

Tack welds welds Cleaning of welds Backgouging Back gougingand and chipping Visual nspection Weld reinforcement Undercutting Peening Repairs

55 55 55 55 55 55 55 55

1 0 Shell insert type reinforcement 11 Barrel type nozzle reinforcement 1 2 Graph for the determination of the thickness of barrel type nozzle reinforcement 1 3 Flanged roof nozzles 1 4 Typical weld details for connection of mountings: set-through ype (preferred details): t = 2 0 mm (max.)

116.1 6 16.2 16.3 17 17.1 1 7 ,2 17.3 17.4 18 18.1 18.2 18.3 18.4 18.5 18.6

Welding approval Generalprocedure andwelderapproval Weldingprocedure Welding procedureapproval approval Approval Approv al pro proces cess s for fo r welders Radiography Application Preparation Preparati on for examination Extent of radiographyper radiographyper ank Radiographyrocedure Radiography rocedure Testing General Botto m testin testing g Mountings Shell testing Floating-roofesting esting Fixed-roofesting Fixed-roof esting

56 56 56 57 57 57 57 57 58 59 59 59 59 60 60 60

1 5 Typical weld d details etails for f or connection of mountings: set-through type (preferred details): 2 0 mm < t < 4 0 mm 1 6 Typical weld details for connection of mountings: set-through ype (preferred details): t i > 4 0 mm 1 7 Typical weld details for the connection of mountings: set-through type (alternative details) 18 Typical weld details for connection of mountings: compensated set-through type (preferred details): t = 12.5 mm (max.) 1 9 Typical weld details for connection of mountings: mount ings: compensat compensated ed set-through set-t hrough typ e (preferred details) 2 0 Typical weld details for connection of mountings: mount ings: dompensated dompensated set-throug set-through h type

Appendices

I

A Recommendati Recommendations ons or tank foundations B Recommendations or the d desi esign gn and applicat application ion of insulation C Standard Standarddiameters diameters for vertical cylindri cylindrical cal tanks D List of symb symbols ols E Recommendations or internalloating covers F Recommendations or the d desi esign gn of venting systems G Seismic rovisions for fo r stora storage anks ge

61 64 75 77 78 80 83

Tables illet of weld 1 Leg length 2 Minimum pecified hickness hell ionsing 3 Angle 4 Minimum sizes of to p curb ang angle le ozzle ndody hickness 5 Manhole 6 Extent f radiography per per tank 7 Acceptance levels for radiographicexamination 8 Standavd engths ength s for fo r shell lates 9 Nominal capacities capacities of stan standard dard vertical cylindrical tanks 1 0 Requirements for emerge emergency enting ncy I I Soil profile coefficient

I

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10 11 14 18 23 58

59 75

75 82 85

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Figures  |   |     |   |   

1 Minimum harpy equirements V impact 2 Typical bottom layouts for tanks 3 Cros Cross s joints in bo bott ttom om p plate lates s where three thicknesses 4 Typical joints in sketch plates under shell plates: tanks up to and includ including ing 12.5 m diameter 5 Typical annular plate joint under shell plates: ver tanks 12.5 m diameter 6 Wind ompression areas 7 Shell-roof 8 Typical ank anc anchora horage ge detail 9 Shell  |     |   |     |   |     |   |     |   |   |   |     |   |   |   

7

9

10

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COPYRIGHT COPYRIG HT 2002; British Standards Institution on ERC Specs and Standards

11 11 13 17 22 24

25 26 27 29 30

31 32 33

34 34

(alternative details) 21 Typical weld details for connection of mountings: set-on ype (shell nozzles less than- 80 mm 0.d.) 0.d.) 2 2 Recognized weld details for connection of mountings 2 3 Reinforcement details or low type nozzles 24 Details of overlay weld for nozzles 2 5 Details of an acceptable type of spiral stairway 2 6 Handrailing 2 7 Typical detail of earthing boss (supplied with tank) s i t e weld welded ed to tank shell plates 2 8 Flush type clean-out door wi th insert plate plate reinforcement 2 9 Flush type clean-out door with plate reinforcement 9 1 5 mm 1230 mm 3 0 Flush type clean-out door wit h plate

35

3 0 0xmm 2 3 0clean.-out mm 31 reinforcement Davit for 9 1 5 mm 1 2 3 0 1mm door

44 98

3 2 Combined water draw-off and clean-out sump 33 Acceptable water draw-off sumps V-notch impact t e s t 3 4 Location of Charpy V-notch specimen 35 Typica Typicall tank foundation 3 6 Pad supports 3 7 Angle section and plate supports 38 Typical flanged nozzle or manhole 3 9 Typical arrangement arrangement showing showing terminati term ination on of insulation adjacent to.the tank bottom 4 0 Typical arrangement wit h insulation attached t o the shell shell only 41 Typical flanged nozzle or manhole manhole wi th additional branch insulation 42 Typical construction of insulation local to 43 44 45 46

wind stiffeni stiffening ng ring r ing Effective masses Centroids of seismic seismic forces Factor K, Compressi Compr essive ve force fo rce Wb

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36 37 38 39

42 43 44 45 47

50

51

56

62 67 67 68

70 70 71 8724 84 85 87

2

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Specification

2.2 Design Design metal temperature temperat ure (see 3.1 (f))

1 Scope

The desig design n metal met al temperature temperatur e shall shall be specified specif ied by the purcha pur chaser ser on the ba basi sis of the of offic fic ial weather reports r eports over over a t least 30 year years. s. The design design metal met al temper tem peratu ature re shall be

This British B ritish Standard specifies requirements requirements or the materials, design, fabrication, erection and testing of vertical cylindrical welded non-refrigeratedsteel tanks. The standard appliesspecifically appliesspecifically to the need needs s of the petroleum industry and and the requirements for fo r the desi design, gn, construction, constru ction, inspection and testing of tank shell shells s apply when the desig design n relati relative ve density of the p product roduct stored st ored wi ll no t be less than 1 O.

the lower of the lowest daily mean mean temperaturet tempera turet plus 1O OC an and d the minimum temperature temperature of the contents. For a sto storag rage e tank constructed construc ted fo forr se serv rvic ice e i n the UK where the shell temperature i s controlled b y ambient conditions, conditions, the minimum de desi sign gn metal temperature shallo ott exceed exceed O C . For a storage tank constructed for use outside the UK and where no long term data or weather reports are available, the design design metal temperature shall shall be the lower of the lowest lowe st daily mean temperaturet temper aturet plus 5 OC and the minimum temperature of the contents. contents.

N O T E l . T h i s p r o v i d e s t h e p e t r o l e u m i n d u s t r y w i t h t h e n e c es es s a arr y o p e r a t i o n a l f l e x i b i l i t y i n t h a t t a n k s o r i g i n a l l y d es es i g ne ne d t o s t o r e o n e parti cul ar pro duc t can subsequ entl y be uti l i zed to store produc ts of di f feri n g rel ati ve densi ti es wh en th e need ari arises. ses.

The standa standard rd appl applies ies to non-ref non-refrigerated rigerated s sto torag rage e tanks w it h the following characteristics: (a) maximum design pressure of 56 mbar*;

In the interest interests s of operational flex ibili ty, the minimum de desi sign gn temperature for the tank shall shall no t take into in to account the beneficial bene ficial effect of heated heated or insulated insulated tanks.

(c) tha t are neve neverr filled above above the level of the top of the cylindrical she shellll or the overflow, whichev whichever er i s lower.

beexchanged exchanged prior o 3 Information to be

(b) (b ) des design ign metal temperature no nott cooler than - 10 OC;

imp lementin g the equirements of this standard and inspections by the purchaser purchaser during erection

N O T E 2. F o r special case casess ou tsid e the s cope o f thi s speci fi cati on where th e desi design gn pressure i es between 56 m b a r a n d 1 4 0 m b a r , r e f er er e n c e m a y b e m ad ad e t o B S 4 7 4 1 f o r ty ty p e s o f r o o f d e s iig gn procedures.

In addition to the definitive requirements, the standard also requires the items detailed in clause 3 to be documented. mente d. For compliance wi th tthis his standard standard,, bo th the defin itive requirements and the documented items hav have e to be satisfied.

3. 3.1 1 Info rmation rmat ion t o be be specified specified by the purchaser purchaser** The following basic information to be specified by the purcha pur chaser ser shall shall be fu lllly y documented documented.. Both the definitive requirements specified hroughout hroughou t the standard and the documented items shall be satisfied before a clai claim m of compliance with the standard can be made and verified.

N O T E 3. T h e t i t l e s of the publ i cati ons referred t o i n thi s sta standard ndard are l isted isted on the i nsi de back cover.

(a) Geogr Geographi aphical cal location of the tank. tank .

(b (b)) Diameter and height or the capacity of the t he tank, including ullag ullage. e. Where only the capacity of the tank is specified ground conditions conditi ons shall shall be included. incl uded.

2 De Design sign co nditions 2.1Designpressure

(see 3.1(e))

(c) Whether fixed or floating roof i s to be supplied

2.1.1 General. I n the interests s standardization tandardization of desi design gn as specified pressures, storage tanks shall beofgrouped i n 2.1.2 t o 2. 2.1. 1.4. 4.

and the type of roof if the purchaser has specific preferences, ¡.e. for fixed roofs (cone, dome, membrane, etc.) o r f o r floating roofs (pontoon, double double de deck ck,, etc.).

2.1.2 Non-pressure tanks. Non-pressure tanks shall be suitable for working a t atmos suitable atmospheric pheric press pressure ure,, bu t designe designed d for an inter internal nal pressu pressure re of 7. 7.5 5 mbar and a vacuum of 2.5 mbar. In a l l cases the tanks shall comply wi th 8.5. For tanks wi th column-supportedroofs, an internal pressure of 4 mb mbar ar sha shallll be assumed assumed..

(dl All releva relevant nt properties of the contained fluid, including the relative density andcorrosion all allowan owance ce (if , how. and where where required). required ). cond itions s (e) The design vapour pressure and vacuum condition inside insi de the tank t ank (see 2.1). ( f ) The minimum minim um and maximum maximu m desi design gn metal temperatures (see 2.2).

2.1.3 Low-pressure anks. Low-pressu Low-pressure re ta tanks nks shall shall be designed for an internal pressure of 20 mbar and a vacuum of 6 mbar.

(9) The size, number and type of a l l mountings required showing locations. Maximum fill ing an and d emptying emp tying rates rates and any special venting arrangements (see 9.9).

2.1.4 High-pressure anks. High-pressure tanks shall be designed desi gned for an inte internal rnal pressure pressure of 56 mbar and and a vacuum of 6 mbar. mbar.

(h) The The minimum depth of product (see lO.l(b)).

(i) f the tank is to be insulated (see clause 12).

'1 m b a r = 100 N / m 2 = 100 Pa. X ( m a x i m u m t e m p e r a t u r e + m i n i m u m t e m p e r a t u r e ). ).

t

-

R

+ W h er er e t h e w o r d ' p u r c h a s e r ' o c c u r s i n t h e t e x t , i t i s i ntended to i ncl ude representati ves of the purchaser, e. e.g. g. purcha purchaser' ser'ss i nspector. --

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COPYRIGHT COPYRIG HT 2002; British Standards Institution on ERC Specs and Standards

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BS2654:1989

E S 1 BS*Zb54

A9

W

Lb24bb9 O LY L3ZA b

U

j ) Areas of responsibility between the designer, the manufacturer and and the erector of the tank when the these se are not the same.

(i )Details of painti painting ng requirements and and whether whether pickling p ickling,, grit or shot blasting i s required (see 13.6.1, 13.6.3 and 14.12).

(k ) Quality of the water (particularly i f inhibiters a arre to

Details-of ls-of erection erection marks (see 13.7.1). (j) Detai

(see e 18.4.2). be present) present) to be use used dduring dur ing tank water est (se (I) Expected maximum differential settlements during waterr testing wate testing and servic service e lifetime life time of the tank (see appendix A).

(k ) Whet Whether her welding welding electrodes and/orkey and/or key plating equipment are are to be supplied by the tank manufacturer

(m) Other specifications specificationswhi which ch ar are e to be read read i n conjunction wi th this stan standar dard. d. alternative information informa tion to be supplied supplied 3.2 Optional and/or alternative b y the purchaser

Th The e following optional op tional and/or alternat alternative ive information in formation to be supplied by the purchaser shall be fully documented. Both the definitive requirements specified hroughout this standard and the documented items shall be satisfied before a claim of compliance with the standard can be made and verified.

(see

14.1).

(I) Altern Alternative ative arrangeme arrangements nts for provision provisi on of tank foundation (see 14.3). (m ) Whether a welde welderr making making only fil le lett welds welds i s required to be approved for such welding in accordance with BS 4871 : Part 1 (see 16.3.2). (n) Whether tack wetding of shell, roof and bottom i s permitted permit ted to be carr carried ied out ou t by non-approved operators (see

16.3.2).

testingof reinforcing plat plates es i s (o) Whether pneumatic testingof required (see 18.3.1).

3.3 Inf orm ati on t o be agr agreed eed bet betwee ween n the purchaser purchaser and and

(a) Whether a check analysis is required (see 4.3.2).

the manufacturer manufacturer

(b) Whether the weight of insulation is excluded from the minimum superimposed loadings (see 5.3.2).

The following follow ing informa info rmation tion to be agreed agreed bet betwee ween n the purchase purc haserr and manufacturer sha shallll be be fu fullll y documented. Both the definitive requirements specified hroughout this standar standard d and the documented itemsshall itemsshall be satisfied before a claim of compliance compliance wit h the standard ca can n be made and verified.

(c) Whether significant external loading rom piping, etc. is present (see 5.5).

(d (d)) Wheth Whether er seism seismic ic loading load ing is present requiring specialist considera consi deration tion includin inclu ding g methods methods and crit criteri eria a to beus used ed in suchanalysis analysis (see 5.7 and appendix G ) . (e) Whether a fixed roof is required and i f so:

(1) i f cone roof slope slope is other than 1 in 5 see 8.2.2); radius ius of curvature curvature of dome roof is other than (2) i f rad 1.5 times tank diameter (see 8.2.2); (3) whether made a s a double-wel double-welded ded lap oin t or a butt joint (see 8.3.5);

(4) whether particular venting requirements requirementsare are specified (see 8.6.1 and 8.6.2). or ( f l Whether a floating roof i s required and i f so: (1) whether floating roof is designed to land as part of the normal operating procedure (see 9.1.1); (2) whether floating roof i s designed for wind-excited fatigue loading (see 9.3); 3) whether top edge of bulkhead is to be provided

single le fil let wel weld d (see 9.5); with continuous sing (4) floating roof ladder details (see 9.6.1, 9.6.2 and 9.6.4); (5) ype of primary roof drains (see 9.7.1); 6)equirements for additional roof manholes (see 9.1 9.1 1);

( 7 ) whether maximum aromatic content o f the product i s grea greater ter than 40 % ( m h ) see 9.13);

(8) requirements for the design of gauge hatch (see 9.14).

(9) An alternative type of manhole cover (see

11.3).

(h (h)) Details Details of fla flange nge drilling if no t n accor accordan dance ce wi th BS 1560 see 11.7).

(a) Alternative materials selection (see

4.1).

(b) Precauti Precautions ons for avoiding britt le fracture during hydrostatic testing (see figure 1). (c) Alternative bottom plate layouts (see 6.1.2).

(d) Spacing of the roof-plate-su roof-p late-support pporting ing member members s for dome roof (see 8.3.1). increa rease se in roof j oi nt efficien e fficiency cy for lapp lapped ed (e) Any inc and welded roof plates (see 8.3.6). (f ) Alternative Alternative loading loading conditions conditions for floating floating roof design (see 9.2.1.4). cleaning position positio n levels of the (9) The operating and cleaning supporting legs (see 9.10.1). (h) Propos Proposed ed method to hold the pla plates tes in position for welding (but see 14.5.1). (i)The location and number of checks on shell tolerances tolera nces during erection ere ction (see 14.6.2). ( j ) Methods of protecting the shell during erection against wind damage, etc. (see 14.9).

(k ) If ixed roofs ar are to be er erec ecte ted d i n tthe he tank bottom, bo ttom, and raised into position by an air pressure or suitable means (see 14.10). (I) Sequence in which joints are to be welded

(see

15.2).

(m ) If previously previously approved.appropriate approved.appropriate welding procedures are acceptable (see 16.1.3). (n) Test procedures to be used during the tank water t e s t (see

18.1.1).

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B S I BSm2b54 B7

m 3b24bb9 01143323

m BS 2654 1989

3.4 Inspections b y the pur purcha chaser ser during erection

The follo win g inspection inspections s b y the purcha purchaser ser during erection sh shal alll b be e fu lly ll y documented. Both the definitive rrequireequirements specified throughout this standard and the documented items shall be satisfied beforea claim of compliance compliance with this standard can be made andverified.

Bessemer steels nor rimming steel shall be permitted to be used. The tank manufacturer shall ascertain rom the steelmaker (at the the time o f order) the condition of supply supply of all plates, e.g. as-rolled, normalized, orquenched orquenched and tempered, and the nominal composition of the steel.        |     |     |

    |   |     |

(a) Rect ifica tion of da dama mage ge to materi materials als prior t o erection (see 14.4).

4.3 Chem Chemical ical composition

(b) Repai Repairr of all unacceptabl unacceptable e defects found fou nd in welds

4.3.1 The carbon equivalent calculated calculated rom the ladle

(see 15.14.1).

    |   |   |     |   |   |   |     |   |     |   |

analysis using the following formula shall not exceed 0.43 % ( m / m ) or plates 20 mm thick up to and including including 25 mm nor 0.42 % m / m ) or plates thicker than 25 .mm.     |   |

(c) Additional Addit ional radiographic testingof welds (see 15.14.2). (d) Records of each welder’s approval (see 16.3.5.1). (e) Standard t e s t radi radiogr ograph aph (see (see 17.4.4).

(f ) Repair Repair of leaks in bottomand bottomand bottom toshell toshell welds (see 18.2.4). (9) Leaks in pontoon compartments and decks (see 18.5.3).

    |     |   |     |   |

Mn

+-

    |     |

C r + M o +i +VC u

6

+-

    -

15

4.3.2 The ladle analysis and check analysis, when required (see 3.2(a)), sha shallll be reported by tthe he steel maker as required by the particular steel specificatio specification n together together with values for all elements specified n 4.3.1 and including any deliberate additions, .g. aluminium, niobium, boron

or vanadium. vanadium. 1n.a 1n.a check check analysis analysis th the e carbon equivalent, equiva lent, usi using ng the form formula ula C + Mn/6 shall not exceed 0.43 % m / m ) (see 3.2 a)). The incidence of testing shall not be less than that Specified in BS 4360.

4 Materials 4.1 Specifications

All Al l materials used used i n the manufacture of tanks complying wi th this standard standard shall shall be be in accorda accordance nce wi t h appropriate appropr iate specifications giv given en i n either (a) or (b), and as amended or amplified by the requirementsof this stánda stándard. rd. i n accordanc accordance e wi th BS 4360 sections and bars: ( I S 0 630-1980*) i n accordance accordance wi th BS 1503 (carbon Forgings: and carbon/manganese steels only) (a) Plates,

Bolting material:

i n accorda accordance nce wit wi t h BS 1506

Piping:

in accordan accordance ce with wi th BS 3602 and B S 3603.

(b) Otherwise suitable materials greed between the purchaser and the manufacturer (see 3.3 a)) provided that th at such such materials are are equivalent i n heat treatment treatm ent and chemical composition to those listed in (a) an and, d, i n other resp respect ects, s, comply w it h a l l the requirements of this standard. N O T E . E x a m p l e s a r e f o r gi gi n g s i n ac ac c o r d a n c e w i t h A S T M A 1 0 5 : 1 9 8 2 t , p i p in i n g n ac ac c o orr d an an c e w i t h A S T M A 1 0 6 : 1 9 8 2 t or A S T M A 5 2 4 : 9 8 0 t o r G r ad ad e s A a n d B o f A P I 5 L : 1 9 8 3 + .

4.2 Steelm Steelmaking aking proces process s

Steels shall be made made by the t he open hearth, electric elec tric furnace

or one of the basic oxygen proce process sses es.. Use Use o f s sem emi-k i-kill illed ed or fully-killed steels shal shalll be permitte permitted d provided that they comply with all the requirements of this th is standard standard.. Neither

4.3.3 For steels wi th specified specified minimum tensile tensile strength strength greater than 420 N/mm* the phosphorus plus he sulphur

shall not n ot exceed 0.08 % ( m / m ) .

4.3.4 Steels shal shalll be either aluminium treated wi th a minimum aluminium/nitrogen ratio of2:l or have a nitrogen content of less than 0.01 % ( m / m ) . 4.4 Notc Notch h du ctility 4.4.1 General. Th The e required impact t e s t temperatures and levels of impact properties fo r shel shelll and botto bot to m annul annular ar plates shall comply with the following clauses, as appropriate, together with 6.1.4 and figure :

< 430 N/mm2 tensile

(a) clause 4.4.2 for materials materials strength;

>

(b ) clause clause 4.4.3 for materials 430 N/mm2 and d 90 N/mm2 tensile tensile strength; strength; (c) clause 4.4.4 for fo r material materials s

strength.

> 490 N/mm2 tensile

For thickness thicknesses es n ot exceeding exceeding 13 mm i n materia materials ls with specified minimum tensile tensile strength strengths s up t o and including 490 N/mm2, impact tests are not required. N O T E . S t ee ee l s m a y b e s u p p l i ed ed i n c o n d i t i o n s o t h e r t h a n n o r m a l i z e d w h e n i t i s to be demons trated to the sati sfacti on of the purchaser purchaser that th e manuf actur i ng procedure (e.g. (e.g. con trol l ed r ol l i ng, quenchi ng and temperi ng, accel erated erated cool i ng, etc.) wi l l pr ovi de equi val ent notch duc tility.

*W hen speci fyi ng I S 0 6 3 0 - 1 9 8 0 , p u b l i s h e d b y t h e I n t e r n a t i o n a l O r g a n i za za t i o n f o r S t a n d a r d i z a t i o n (1801, i t i s recommended that reference

i s made to t h e a p p r o p r i a t e n a t i o n a l s t ee ee l s t a n d ar ar d f o r t h e p u r p o s es es o f s p e c i f y in in g a d d i t i o n a l r e q u i re re m e n t s n o t i n c l u d ed ed t h e r e i n .

t P u b l i s h e d b y t h e A m e r i c a n S o c i e t y o f M a t er er i a ls ls a n d T es es t i n g a n d av av a i lla able from the L ibrary, BSI, L i n f o r d W o o d , M i l t o n K e eyy n e ess M K 1 4 6 L E .

..”

+Pub jshed jshed b y theA theA m e r i c a n

P e t r o l e u m n d u s t r y a n da da v a aii l ab ab l e f r o m h e L i b r a r y ,

COPYRIGHT COPYRIG HT 2002; British Standards Institution on ERC Specs and Standards

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B S I, L i n f o r dW dW o o d , M i l t o n

K e y ne ne s M K 1 4 6 L E .

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B S 2654 : 1989

4.4.2 Mater Materials ials wi th spec specified ified minimum tensi tensile le streng strengths ths less than or equal to 430 N/mm2, thicker than 13 mm. Materials Material s with wit h specified specified minimum mini mum tensile tensile strengths strengths less than or equal equal t o 430 N/mm2 and thicker than 13 mm shall

minimum specified specified yield strength for the shell plates plates to which they the y are attached. Nozzle No zzle bodies shall also omply omp ly with wi th thes these e requirements requirements when he nozzle body is used in the reinforcement calculation.

be impact tested and show not less than 27 J Charpy V a t t 2 0 "C or a t the t e s t temperature indicated n figure 1,

4.5.2 Permanent Permanent attac attachments hments,, reinfor rein forcing cing plates, plates, nsert plates, plat es, nozzle nozzle bodiesand bodiesa nd langes langes shall shall comply com ply with wi th the notch notc h duc til ity requirements of 4.4. .4. The reference thickness shall be taken as the nominal thickness of the component except for the following,

whichever is the lower. Three specimens shall be tested, the val value ue taken being the minimum mini mum av aver erag age e of the three results. resul ts. The The minimum mini mum individual individu al value value shal shalll be not less than 70 % of the specified specif ied mi minim nimum um average average value. ue.

design met al tem peratu re iiss t10 C o r a b o v e , NOTE. Provi ded the design

i t i s not necessa necessary ry to test materi al s wi th a speci fied fied m i ni mu m y i el d strength no t exceeding exceeding 300 N / m r n * and less than 20 mm t h i c k .

4.4.3 Materials with specified minimum tensile strengths greater than 430 N/mm2 and up t o and including 490 N/mm2, thicker than 13 mm. Materials Materials with wi th specified specified minimum tensile strengths greater than 430 N/mm2 and up t o and including 490 N/mm2 N/mm 2 and thicker than 13 mm shall shall be impact tested and show not less than 41 J Charpy V a t - 5 O C or a t the t e s t temperature indicated n figure 1, whichever i s the lower. Three specimens shall be tested, the value taken being he minimum average of the three results, The minimum mini mum individual individua l value value shal shalll be be not less than 70 % of the specified minimum mini mum averag average e value. value. 4.4.4 Mate Materials rials wi th specified mini mum tensi tensile le stre strengths ngths greater than 490 N/mm2, all thickne thicknesses. sses. Mate Materia rials ls wi th specified minimum mini mum tensile strengths greater than 490/mm2 and of all thickn thicknesses esses shall be impact imp act tested and show not no t less than 41 J Charpy V a t - 15 "C or a t the t e s t temperature indicated in figure 1, whichever is the lower. Three s p e c i mens shall shall be be tested, tested, the value value taken ta ken being the th e m mini inimu mum m average of the three results. The minimum individual value shall be not less than 70 % of the specified minimum average value. 4.5 Mountings 4.5.1 Reinfor Rein forcing cing plates and nsert plates shall have a minimum specified specified yield strength not less than 90 % of the

(a) Welding neck flanges. The reference thickness shall be taken as the thickness a t the weld or 25% of the flange thickness, whichever s greater. b ) Hubbed or slip-on sli p-on flanges. The reference thickness shall be?aken as the nominal thickness of the branch to which the flange i s welded or 25 % of the flange thickness, whichever i s greater.

(c) ßeinforcingplates. The reference thickness shallb be e

taken as i t s nominal thickness and f such plates exceed 40 mm thick, they shall show not less than 27 J Charpy V a t -5 0 'C, irrespe irrespective ctive of the minimum minim um design design metal temperatur tempe rature. e. Three pecimens pecimens shall shall be be tested, tested, the value taken being the minimum average of the three results. resul ts. The minimum mini mum individual individu al value value sha shallll be not l e s s than 7 0 % of the specified minimum mini mum averag average e valu value, e, 4.6 Other requirements 4.6.1 The measured thickness a t any point more than 15 mm from the edge of any shell (whose thickness shall comply with wi th 7.1.3 7.1.31, 1, bottom, bottom , rroof oof or annular plate shallnot be'less less than the specified thickness less half the total tolerance toleran ce given in table 8 of B S 4360 1979. 4.6.2 The measured thickness a t any point more than 1 5 mm from the edge of shell plates whose thicknesses have been been calculated in acc accordanc ordance e wi th 7.2. 7.2.2 2 to be gr greate eaterr tha than n as speci specified fied in 7.1. 7.1.3, 3, sha shallll no nott b be e less than the calculated calculated minimum thickness. thickness.

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S ca le B S c a l e A +2

o

42

o

+15

S c a l e A - M i n i m u md md e s i g nm nm e t a l temperature O C (se e 2 .2 ) S c a l e B - M i n i m u mw mw a t e r e m p e r a t u r e

t

...

.

...

. . . . I .

v

W

L

 

 |     |   

c

+1 5

W

.-E .-

 |   |     |   |   

E

 |   

I

 |   |   

v v

 |   |     |   |     |   |   |   |     |   |   |     |   

W

c

Y

.-u

.c

+lo-

c

 |   |   

W

u

c

 |   

W

 |     |    -

L

u-

W

L

.-CI

5

L

al

c

r

0-

-50

-4 O

-10

-30

-20

Charpy

V test emperature

O

+10

+

20

C

(Intermediate values may be determined by interpolation.) NOTE. Scale Scale A on he ordinate i s to be us used ed in determining determining m inimum Charpy V requirements for the thickness and minimum design temperature concerned. For the purposes of this note, conversion of the measured impact value to the 27 J (or 41 J for ste e l s wi th specified mini mum tens ile strength greater greater than 430 N/m m') value may be made on the basi basis s of 1.35 J per C, uc uch h extrapolation being being limite d to a maximu m range of 20 OC. For example, i f t he actu al valu value e by test equivalent test i s 33.75 J a t -2OOC for a steel of specified minimum tensile strength greater than 400 N/m mz , the equivalent temperature for 27 J may be assumed to be -25 OC. The requirements derived from sca scale le A take i nto account an improvement i n safe safety ty wh ich may be anticipated as a result of the hydrostatic t e s t . Durin During g the first hydrostatic e s t the degree of security against brittle fracture may be iather less than onsubsequent on subsequent loading. Attention i s drawn to the more conservative requirements of scale B when consideration is to be given given to the us use e of this sc scal ale e during hydrost atic esting of tank shel shells ls con constructed structed of steels wit h specified specified minimum tensile strength greater than 430 N/mm* . The application of scale B, or any alternative procedure regarding the precautions safeguard rd the tank f rom bri ttl e racture, is the subject of agreement between the to be taken during water testing to safegua purchaser and the manufacturer (see 3.3(b)).

Figure 1. Minimum Charpy V impact requirements

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BS 2654 : 1989

5 Design oadings

three second three second gust speed speed shal shalll be obtain obt ained ed fr from om the t he approapp ropriate authority.

5.1 General General

NOTE. Careful consideratio n should be give given n t o op en-top water tanks without any form of roofsince roof since wind effects could produce severe movement of the contents resulting in spillage and excessive loading on the tank. If this loading cannot be quantified, it is recommended that a roo f be provid ed unless previous experience experience with similar conditions has proved satisfactory.

The tank shallofbethe designed for f orspecified theified most mosint severe possibl combination loadings spec 5.2 t o possible 5.7. e 5.2Dead 5.2Dead oads Dead loads shall be considered as those those resulting from the t he weight of a l l component parts of the tank. weight 5.3 Superimposed Superimposed oads

5.7 Sei Seismi smic c oads ( i f applicable) applicab le) The purchaser shall specify whether the tank tan k i s to be designed t o with withstan stand d seismic seismic loads loads (see 3 . 2 d ) ) . NOTE. Recommendations on seismic provisions for storage tanks

5.3.1 The fixed 5.3.1 fix ed roof and and supporting suppo rting structures stru ctures sha shallll be designed to support a minimum superimposed load of 1.2 kN/m kN /m Z of pro project jected ed area, area, The superimposed superimposed oad shall shall be th the e su sum m of either inter int ernal nal vacuum and snow load, load, or internal inte rnal vacuum vacuum and live load.

are given in appendix G.

5.3.2 5.3. 2 Unless Unless otherwise othe rwise specified by the purchaser (see 3.2(b)) 3.2(b)),, the weight of any insulation insulat ion sha shallll be included in the minimum superi superimpos mposed ed loadi loadings ngs for fixed roofs

6.1General

specified in 5.3.1, 5.3.3 5.3. 3 The superi superimpos mposed ed oadin oadings gs shall be as specified in clause clause 9.

applied to ffloat loating ing roofs ro ofs

5.4 Contents The load due to the contents conte nts shall shall be the weight of the product to be stored from full toemp empty, ty, with or witho ut the specified vapour pressure, For the design design of the th e shell, the produ p roduct ct relative density sha shallll be as assu sume med d t o be no nott less than 1 O. '5.5 '5.5 Loa Loads ds resulting result ing from fr om connected piping pipin g Pipes, valves and other items connected o the tank shell shall be designed designed in such a manner that no significant additional loads or moments are applied to the tank shell. Settlement of all pipe support oundations ou ndations relative to those those of the tank, rotational an and d translational translat ional moveme movements nts of the lowest shell course shall be taken into consideration. The purchaser shall s t a t e whet whether her this loading is significant (see 3 . 2 ( c ) ) , otherwise it shall not be taken into account. 5. 5.6 6 Wind oading wind d speed speed us used ed in the th e calculat calc ulations ions shall shall be tthe he The win

maxim ma ximum um hree hre e second second gust speed estimated estimatedo be exceeded on the average only once in 50 years. In the UK this value shall be taken as 'design wind speed' a s defin defined ed in CP 3 : Chapter V : Part 2, I n oth other er areas areas the th e

6 Bottom design

6.1. 6.1.1 1 Full support of the tank bot tom to m by the foundation foundatio n shall shall beassumed. NOTE. Recommendations for tank foundations and typical tank pads are given in appendix A .

6.1. 6.1.2 2 Bottoms for tanks up t o and including 1 12.5 2.5 m diameter shall normally be constructed from rectangular plates plates,, wit h sketch sketch pla plates tes to the perimeter. I n particular cases, by agreement agreement between the purchaser purchaser and the manufacturer (see 3.3(c)), a ring of annular plates or other layouts are permitted. The specified thickness of the rectangular, sketch and annular plates shall be no t less than 6 mm (see 4.6.1). 6.1. 6.1.3 3 A l l tanks greater than t han 12.5 m diameter shall have a ring of annular plates having the ollowing minimum thicknesses: (a) 8 mm, when when tthe he bo tt om course course of shell plating plat ing i s 19 mm thick or less;

(b) 1O mm, when the bottom course of shell plating is over 19 mm up to and and including 32 mm thick; (c) 12.5 12.5 mm, whe when n the bot tom to m cour course se of shell plating is

over 32 mm thick.

The specified thickness of both the rectangular plates and the sketch plates shall be not l es s than 6 mm (see 4.6.1). 6.1.4 The annular plates shall have a minimum width of 500 mm and shal shalll be of th the e sa same materi mat erial al specif sp ecificat ication ion with wi th resp respect ect to strength a and nd impact requirements s the bot tom to m cou course rse of shell shell plate. 6.1.5 6.1.5 The minimum mini mum distance fro m the outer surface surface of the shell plates to the outer edge of the bottom plates shalll be in accordance wi t h sections D - D and E - E of shal figure figu re 2.

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.

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B S 2654 : 1989

 

 |     |     |   |     |   |     |     |   |     |   |     |   |     |   |   |   |     |   |   |     |     |   |   

 |     |     |    -

. -. ...,"...""" .

and sketch plates see 6.1.3.

Section 0 - 0 (a) Typi Typical cal bottom layout for tanks tanks up toand toand including 12.5 m diameter

Shel l p l a t e Annular Sketch p

6 0 ' 360 min. m i n .

SO

min.

Section E - E Fillet weld size, see 6.2.4.

figure 5 (b) Typical bot tom layout for tanks over over 12.5 m diameter For layout o f plates similar to sections sections and B B see (a). A - A e stated. Dimensions are are i n mil limetres, unless unless otherwis stated.

Figure 2. Typical bottom layouts for tanks (see clause 6)

For thickness o f annular, rectangular and sketch plates see 6.1.3.

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COPYRIGHT COPYRIG HT 2002; British Standards Institution on ERC Specs and Standards

9

-.  

~~

B S I BS*Zb54

~

87 W 3 6 2 4 6 6 7 3 4 3 3 3 4

3

m

B S 2654 : 1989

6.2.4 The attachment attachment between the botto bot tom m edg edge e of the

6.2 Design 6.2.1 All joints in rectangular and sketch plates shall be

lapped, lappe d, They They s shall hall be welded welded on the to p side side only on ly w it h a ful l fill et weld, wel wit(see h a minimum lap of of figure five times thickness of d, theand plate section C - C 2). the

The rectangular plates and the sketch plates shall be lapped over the annular ring of segmental plates where these are used. They shall be welded welded on the top to p side only with a full fil le lett weld and the minimum minimu m lap s shal halll be 60 mm (see section E - E of figure 2). At the ends of cross joints in rectangular plates and sketch plates where three thicknesses thicknesses occur, the upper plate shall be hammered down and welded as indicat indicated ed i n detail A or B of figure 3 as a corrective measure if the upper plate overlaps the lower plate. m 6.2.2 For tanks of 12.5 m diameter diameter and unde under, r, the en ends ds of the joints in the sketch plates under the bottom course of shell plates shall be welded fo r a minimum distance of shown n i n figure 4, 150 m m as show 6.2.3 For tanks exceeding 12.5 m diameter diameter,, th the e radial ra dial seams connecting theends theends of the annular segmental plates shall be full penetration butt-welded; a backing strip weld o f the form shown shown in figure 5 i s acceptable.

lowest cours course e of shell plates and the bo bott ttom om sketch plate or annular plate shall be fillet-welded fillet- welded co continuo ntinuously usly on both sides of the shell plate. The leg length of ea eac ch fil le lett weld shall shall be be equal equal to the th ickness of the sketch plate or annular plate (see sections D - D ond E - E of figure 2), except that they shall not exceed the appropriate value given given in table 1 when the shell plate thickness i s less than the b ott om plate thicknes thickness. s. Table 1. Leg length of fillet weld S hel l pl ate thi c k nes s

Leg length of fillet weld

mm 5 ver 6 and

6 8

(see 2.1.41, special I n the des design ign of high-pressure consider consideration ation sh shal alll b be eg giv iven en to tanks the l imi tat ion of upl ift n the tank tank bott om (see clause IO).

Typical layouts for tank bottom plates are shown in sections A-A and B - B of figure 2.

Detail B

s9szLm

Section X - X

EiS2Bz4 Section Y - Y

Figure 3. Cross joints in b o t t o m plates where three thicknesses occur (see 6.2.1)

4

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BSI B S * Z b 5 4

87

m LhZLtbb7 0 1 4 1 3 3 5 3 m BS2654:1989

Backing

Section Z-Z

All dimensions are in millimetres.

t

Figure 4. Typical joint s in sketch sketch plates plates under shell plates: plates: tanks tanks up toand toand including 12.5 12.5 m diamete diameterr (see 6.2.2)

1.5 Section F

 

-F

All dimensions are in millimetres.

 |     |     |   |   

Figure 5. Typical annular plate oin t under shel shelll plates: tanks over 12.5 m diameter (see 6.2.3)

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 |     |     |    -

7 Shell design 7.1Design 7.1Designstresses stresses 7.1.1 The maxim 7.1.1 ma ximum um allowable allowab le desig design n stress stress i n any plate shall be 260 N/mmz or two-thirdsof two-thirdsof the material specifi specified ed minimum yield strength (in N/mm2) t room temperature for a l l tank courses, whichever is the lower. Where the operating temperature s over 150 OC, consider consideration ation shall be given to the effect of that temperature on the yield strength, 7. 7.1. 1.2 2 I n calculating thethickness of plate required, required, he joint as .O. efficiency factor has been taken No relaxation shall be permitted permit ted to the requirements of this t his standar standard d with wi th regard regar d to the approval of o f procedures procedures and welders welders (see clause 16) and the s i t e inspection of shell shell joints (see clause 17). 7.1. 7.1.3 3 I n no case shall the specified thickness of o f shell plates be less than is given given i n table 2 (see 4.6.1). The maximum thickness of shell plates shall be 40 mm.

Table 2. Minim Minimum um specified specified shell thickness Nominal tank diameter

Specified shell thickness t

D

m

mm D< 5 12.5 m m 25 m m h i c k : (c) pl ates > 25 m m t h iicc k : 6 m m .

(b ) pl ates ates

8 mm;

14.6.6 Plates to be joined by but t welding shall be matched accurately and accurately and retained in position during the welding operation. opera tion. Misalignment of the plates shall no nott exceed exceed the following.

14.4 Rectification o f damage to materials Any dama damage ge t o materi material al s shal halll be corrected corre cted to the satisfacsatisfactio n of he pur purch chas aser er prior to erection (see 3.4 a)).

(a) In completed vertical joints: 10 % of the plat plate e

plates tes 14.5 Erection of pla

thickn thickness ess,, or 1. 1.5 5 mm for plates 19 mm thick thic k and under, and 3 mm fo forr plates over over 19 mm thick, whichever i s the larger.

proposed to hold ho ld the pla plates tes in position 14.5.1 The method proposed for welding shall be approved by the purchaser, unless such approval has already been given in writing byhe byhe purchaser

(b) In complete completed d horizontal joints: 20 % of the upper plate thickness, or 1.5 mm for plates 8 mm thick and under, and 3 mm for plates over 8 mm thick, whichever is the smaller.

(see 3.3 h)).

14,5.2 The course of shell plates to be erected first shall be

held i n position by metal clamps clamps or other devic devices es attached to the bo botto ttom m pla plates tes whilst it i s plumb plumbed ed and che checke cked d for fo r circuladty and befare it is tack welded or welded. welded. I n setting ----7 COPYRIGHT 2002; British Standards Institution on ERC Specs and Standards

12.5 m m t h iicc k : 10 m m ;

NOTE . The ank she ell l s h o u l d b e c h e c k ed ed f o r c i r c u l a r i t y , d i m e n s i o n s a n d l e v el el b e eff o r e t h e r o o f m em em b e r s a r e p o s i t i o n e d o r t h e p r i m a r y w i n d g i r d er er i s erected.

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53

 

BSI B S 2654 1989

14.7 Floating-r Floating-roof oof tole toleranc rances es

14.12 Final surface finish

The difference in the gap between the shell and the periphery of the roof on completion of erection of the roof shall not exceed ? 13 mm from fro m the nominal g gap ap..

The final surface preparation and painting system shall be specified by the purchas purchaser er in accordan accordance ce wi th the environ env iron-mental and and operational conditions cond itions (see 3.2(¡)).

NOTE. A t any elevation of the roo f o ther tthan han that a t which it was erected, this difference in gap gap should not exceed f 50.mm or such other value a s may be agreed between the purchaser and the manufacturer for a particular seal design.

15 Welding

cutting ting 14.8 Manual oxygen cut

15.1 Welding process

manuall oxyg oxygen en cu cutting tting i s used for trimming 14.8.1 If manua

inclu ding repair, tack and attachment 15.1.1 All welding, including welding, shall shall be carr carried ied out according to the welding procedure established in 16.2 and by welders approved under 16.3.

outside circumferential edges of roof and bottom sketch pl plat ates es and and for trimming trim ming corne corners rs of bott bo ttom om plate plates s where two lapped joints intersect, such oxygen-cut edges shall be properly cleaned for welding and free from oxide and cutting scale. welding ng edg edges es NOTE, These should be reasonably smooth a t the weldi although this would not normally require grin although grinding ding if a good quality of workmanship is achieved. It is particularly important for the sketch to annular plate connection to be properly prepared and fitted for welding,

14.8.2 When openings for fittings fixed on site are manu ally oxygen manually oxyg en cut, cu t, th then en radius arms, strai straight ght edges edges and and nozzle guides shall be used. The cut edge shall be cleaned and trimmed by chipping or grinding where necessary to maintain the correct weld preparation. 14.9 Protect Protection ion of shell shell during erection The erection contractors shall employ suitable methods or the protection of the shell during erection which have been agreed with the purchaser (see 3.3( 3.3(j)). j)). Wh Whe en required by the purchaser, full details of these methods shall be made available for his approval, The factors to be taken into account when determining thesuitability thesuitability of the proposed method of protection shall be: (a) tank size;

(b) construction method; (c) loca location tion and d degr egree ee of exposu exposure re to wind loads; loads;

NOTE. Unless otherwise agreed between the purchaser and the manufacturer, this standard is confined t o manual metal-arc and

mu ltiCO, -r un subme submerged rged-arc -arcspray welding proce processe sses s for all se seam ams. s. Add itio nally, welding using transfer is permitted for welding girth seams only. When it is proposed to uti liz e welding proces processes ses or techniqu techniques es other than those specified in this clause, it may be nec necess essary ary to mo di fy or amplify the approval tests and/or inspection to ensure satisfacto ry results. For exampl example, e, singl single-pas e-pass s bu tt welds may introdu ce speci special al notch du ctil ity problems problems both in the the weld metal and heat heat-affected zone and dip transfer welding pro proces cesses ses could introd uce lack of fusion anctcold lapping which are not easy to detect. Additional t e s t s and/or inspection will be the subject of agreement between the purchaser and the manufacturer.

15.1.2 Wher Where e manual manual metal-arc metal- arc welding weld ing s employed in

construction, hydrogen-controlled electrodes shall be used for welding steels with wi th specified specified minimum min imum tensile tensile strengths strengths greater than 430 N/mm2 in thicknesses exceeding 13 mm.

15.2 Welding sequences The sequen seqbetween uences ces wh which ich join jo ints ts and are manufa to be welded be (see 3.3(1)), agreed betwe eninhe purchaser man ufactu cturer rer shall and the they y shall beadhered o on site. The sequence employed for tack welding and and welding the bottom, botto m, shell shell and roof ro of pl plate ates ss shal halll be such such tha thatt the th e distort dist ort ion du due e to welding we lding shrinkage is minimized,

(d ) n numbe umberr and type of key plate equipment;

15.3 Vertical joints

(e) availability of reliable meteorologicald data ata during all periods periods of erection.

I n vertical joints in shell plat plates es exceed exceeding ing 13 mm thick, a ll but the root runs shall be welded by the 'upwards' technique. Root Ro ot runs by either the 'upwards' technique or by vertical-down welding in such plates over 13 mm shall be permitted but, in the latter case, the weld metal shall shall be be complet com pletely ely removed by gouging or other suitable suitab le me mean ans s to sound clean metal, before bef ore welding weld ing on the th e reverse side. side.

NOTE. The use of s t eel wire guys or cables may not necessarily b e adequate and consideration should be given o the use of temporary wind girders.

14.10 Erection of fixed roof The.temporary support suppor t for the erection of roof framing fr aming shall remain in position until the completion of the main and secondary framing, Care shall be taken when assembling roof sheets on the framing hat no excessive unsymmetrical loading s applied to the roof members due to the stackingof roof she sheets ets.. Thestren strength gthof the temporary supportt shall b suppor be e calculate calculated d usin using g the most unfavo unfavourable urable loading condition during erection.

15.4 Weather conditions

When ag When agre reed ed w it h th the e purchaser (see 3.3( 3.3(k)), k)), roofs are are permitte perm itted d to be e erect rected ed on the tank bot tom and rais sed ed into position by an air pressure or other suitable means.

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14.11 Erection holes Erection holes holes s sha hallll not be permit permitted ted in plate work. ...

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COPYRIGHT COPYRIG HT 2002; British Standards Institution on ERC Specs and Standards

54

Welding shall not be done when the t he surfaces of the parts to be welded are w wet, et, when rain or snow i s falling on such sur surface faces, s, or d durin uring g periods of high winds unless the welder and work are properly shielded. When the parent metal temperature i s lower than O OC, he surfaces on both sides of the joi nt shall shall b be e preheated preheated to a temperature warm o the hand, hand, o orr t o tthe he temperature specified specified in the welding procedure, and to a dist distance ance of not less than four times the plate thickness or 75 mm, whichever is the greater, in any direction before welding s beg begun. un. During the course course of the welding operation this preheat temperature shallbe be maintained in th the e specif specified ied area. area. |

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15.5 Preheating

15.10 Visual inspection

The necess necessity ity for and and the ext extent ent of prehe preheat at for any of the conditions conditio ns sh shal alll be determined before he procedu procedure re tests are carried out.

All welds shall be visu v isuall ally y inspected.

N O T E . P r e h e a t i s not n or m al l y nec es esss ar aryy o n pl ates less t h a n 25 m m t h i c k f t h e t h e r m a l n p u t i s n o t less than 1.6 k J l m m a n d t h e m a t e ri ri a l c o m p llii e ess w i t h d a u s e 4.

The weld weld metal of bot h sides of a ll bu tt joints shal shalll b be e built up so that the finishe finished d ffac ace e in the are area a of fusion extends extend s above the surface of the th e adjo adjoinin ining g plate plates, s, or the thinner plate joined (see 16.2 and 16.3).

For plates thicker than 25 mm and for a l l thicknesses if inpu t deriv derived ed fr from om the t he welding pro proces cess s i s less the thermal input than 1.6 kJ/mm, the necessity necessity fo forr preheat shall receive special consideration (see BS 5135).

15.6 Electrodes Electrodes shall be stored in their original packets or cartons carton s in a dry plac place e adequ adequatel ately y protected fr from om weather effects. Similar precautions shall be taken in the storage of flux fl ux for sub submer mergedged-arc arc welding. N O T E , I f th th e el el e c tr tr o d e s b ec ec o m e d a m p b u t a r e n o t o t h e r w i s e dam aged, aged, they m ay be used used onl y after bei ng dr i ed out i n a m anner a p p r o v e d b y t h e e le le c t rro o d e m a n u f a c t u r e r . A n y e l ec ec t r o d e s w h i c h have areas of t h e f l u x c o v er er i n g b r o k e n a w a y or d a m ag ag e d a arr e t o b e di s c ar ded.

Hydrogen-controlled electrodes shall be stored and baked in accorda accordance nce wi th the electrode manufacturer's recommendations,

15.7 Tack welds Tack weld Tack welds s used in i n the assembl assembly y of the vertical joi joints nts of tank she shelllls s and horizontal jjoints oints to be manually weld welded ed shallll be re sha remove moved d and sh shall all no t remai remain n i n the fini finished shed joi nt nt.. N O T E . Ta Ta c k w e l d dss i n t h e b o t t o m , s h e l l -t -t o - b o t t o m , r o o f and a u t o m a t i c a l l y w e l d e d h o r i z o n t a l j o i n t s o f t h e t a n k s hel l and oth er j oi nts , need not b e r em ov ed pr ov i ded they ar e s ound and the s u b s eq eq u e n t w e l d r u n s a r e t h o r o u g h l y f u s e d i n t o t h e t a c k w e l d s .

Cleaning ing o off welds welds 15.8 Clean Each run of weld metal shall be cleaned of slag and other deposits before the n ext ru n i s applied. Slag shall also

15.1 1 Weld reinforcement

15.12 Undercutting

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The edges of a l l wel welds ds shall merge smoothly w it h the surface of the plane without a sharp angle. There shall be no undercutting of the parent metal, except that o on n horizontal bu tt joints and fillet we weld lds, s, an undercut not exceeding 1 mm in depth shall not be caus cause e for rejection.

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15.13 Peening

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Peeni Pee ning ng of bu tt weld welds s shall not be permitted.

15.14 Repairs 15.14.1 All unacceptable defects found in welds shall be

brought to t o the at attenti tenti on o off the purcha purchaser ser and his app approv roval al shall be obtained as to the method of repair (see 3.4 b)).

15.14.2 When a section of weld is shown by radiography

not tocomply tocomply with this standard, two adjacent spots shall be examined by radiography. I f th the e weld a t either of the these se sect section ions s fails t o comply with 17.4.10, then either o f the ffollow ollow ing co cours urses es sh shall all b be e followed: (a) additional nearby spots shall be examined until the

limits of such welding are determined; o r (b) a l l welding performed b y the welder welder in that join t shall be replaced. In case (a), (a), i f any additional spot fails to comply with 17.4.10 the limi li mi t of suc such h welding sha shallll be determine determined d

be remove removed d from finished welds welds before b efore insp inspection, ection, Wher Where e air-arc gougi gouging ng i s use used, d, the surfaces surfaces shall be chippe chi pped d or ground back to bright metal before welding.

as specified for the initial section of the defective weld. For case b ) , the purchaser shall be permitted to request that one radiograph be taken a t any selected location on any other ot her jo in t that the s sa ame welder has welded (see 3.4 c)).

gouging and and chipping 15.9 Back gouging

15.14.3 Al l defects in exc exces ess s of the t he mini minimum mum requiremenfs specified specif ied in 17.4.10 shal shalll be remo removed ved by chipping, chi pping, grindin gri nding g

The reverse reverse side side of fu ll penetration b ut t weld welds s shall shall be clea cl eane ned d thoroughly prior t o the application of the fir st run to this si side de in a ma manne nnerr that w il l leave the exposed surface surface suitable suitab le for proper interfusion wi th the deposited weld metal.

or gouging gouging from one or bo th si side des s of the joint, j oint, as required, and rewelded. Only sufficient cutting-out of the joints shall be done-as s nece necess ssar ary y t o remove the defects.

15.14.4 A l l repairs carried out because of non-compliance with 17.4.10 shall be 100 % radiographed unless unless the

N O T E . T h i s m a y b e d o n e b y c h i p p i n g , g ri ri n d i n g , f l a m e or air-arc g o u g in in g o r , w h e re re t h e b a c k o f t h e i n i titi a l b e a ad d i s smooth and free f r o m c r e vi vi c e ess w h i c h m i g h t e n t r ap ap s l a ag g, by other m ethods which may, u p o n f i e l d i n s p e c t i o n , b e a c c ep ep t a b l e t o t h e p u r c h a s e r .

COPYRIGHT 2002; British Standards Institution on ERC Specs and Standards

com comple plete te se seam am is remove removed d and rrewelded ewelded; whic which h case original w eld weld ins inspection pection proced pro cedure ure s shal halll ;beinfollowed followed. . the

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BS2654:1989

16 We Weldin ldin g proce procedure dure and welder approval

provided the process and consumables have been approved on a weld t e s t plate i n accor accordanc dance e wit h BS 4870 : Part 1.

16.1 General

16.2.3 E x a m i n a t i o n o f test plate. Each butt-welded t e s t plate shall be prepared prepared and radiographe radiographed d in accordance with BS 4870 : Part 1.

weld ing proce process sses es to be us used ed for the const c onstrue rue 16.1.1 The welding

16.2.4 Destructiv e testing testing

ti on of the tank shall shall be used used in the procedur pro cedure e and welder approval tests.

Destructive ctive testing te sting shal shalll be i n accordance accordance 16.2.4.1 General. Destru with B S 4870 : Part 1 .

16.1.2 A l l welding procedures shall be approved approved in accord acc ordance ance wit h 16.2 and all welders shall be approved in accord acc ordance ance wit h 16.3.

Wher Wh ere e impa impact ct testing te sting of the plate material materi al i s specified shal alll be (see 4.41, then impact testing of the weld metal sh carried out. 16.2.4.2 Impact tests. Charpy V-notch impact t e s t specimens shall be selected, machined and tested as shown in figur figure e 34 and in i n accordan accordance ce wi th B S 1 3 1 : Part 2.

16.1.3 Previously approved procedures shall be acceptable

asagreed between purchaser andmanufacturer (see 3 .3 ( m) ) .

16.2 Welding procedure approval 16.2.1 Procedure details. The welding procedure specifica-

tio n shall give all deta details ils of the welding proces processe ses s to be us used ed by the contractor, including those for repair, tack and attachment welds and shall also also includ include e the the results of such approval te s ts as required by this stand standard. ard.

16.2.2 Nu mb e r a n d t yp e s of test plates, The number and types of t e s t plates shall be in accordance with B S 4870 : Part 1 and this standard, standard, When s t e e l s with specified minimu min imum m tensile tensile strengths strengths greater th than an 490 N/mm2 N/m m2 are are used in construction, the highest tensile grade of steel to be us used ed i n con constru structio ction n sha shallll be us used ed in approval testing. Procedure te s ts for nozzle (stres (stress s relieved or as welded) repair, tack and attachmen attac hmentt welds are arenot not normally required

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The weld metal of vertical shell shell b ut t welds welds and of manual metal arc welded shell ut t weld welds, s, includi including ng the connections between nozzles and mountings mounting s and and the shell, shall meet 27 J minimum average Charpy V impact energy at the same t e s t temperature a s required by 4.4 for the plate material. When Wh en connections are are made made bet betwee ween n materials of diff differe erent nt thickness, the reference thickness for figure 1 shall be that of the thicker part p art joined. When Whe n gi rt h seam seams s ar are e welded w elded by an aut a utom omat atic ic proces process, s, the Charpy V impac impactt energy energy shall shall no t be less than 27 J minimum mini mum av aver erag age e a t - 1 0 "C or a t a temperatu temperature re indicated by figure 1 using scale A , whichever i s the least onerous. Three specimens shall be tested, the value taken being the minimum average of the three results.The results.The minimum . individual individ ual value value sh shall all be be no nott less than 70 % of the specifi specified ed minimum average value.

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b) Horizontal

jolnts

c r o o tgtg a pa pa n dn dn o t c h

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A l l d i m e n s io io n s a re re i n m i l l i m e t r e s .

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Figure 34. Location o f Charpy V-notc h impact t e s t specimen (see 16.2.4.2)

COPYRIGHT 2002; British Standards Institution on ERC Specs and Standards

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specimen fails t o 16.2.4.3 Retests. If one or more Charpy specimen comply compl y with 16.2.4.2, thre three e fur the therr speci specimen mens s sha shallll be prepared and tested.

I f any of the retests retests fail t o comply wi th 16.2.4.2, the procedure cedu re shall shall be deemed deemed no t to tocomply comply wi th this standar standard d and a new procedure shall be be tested. tested. NOTE. Hardness. I t i s ''rr e cco ommende ed d t h a t it i s d e m o n s t r a t e d i n t h e

p r o c e d u r e t es es t s t h a t t h e h a r d n e ess s o f t h e h e a t - a f f e c t e d z o n e a t t h e s h e llll t o b o t t o m p l a t e a n d o f t h e w e l d m e t a l , e a t --a a f f ec ec t e d z o n e a n d p a r e n t p l a t e a t o t h e r l o c at at i o n s i n t h e s h e llll , s h o u l d n o t e x c e ed ed 300 H V (using 30 kg l o a d ) .

W h e r e w e t H,S c o n d i t i o n s a r e t o b e e n c o u n t e r e d a n d a n a p p r o p r i a t e low l e v el el o f h a rrd dness canno t be obtained, the most 'suitable w a y t o a v o i d s ttrr es es s c o r ro ro s i o n c r a c k i n g w i l l b e t o p r o t e c t t h e s h el el l to an nul ar wel d ar ea and i h e adj ac ent v er ti c al s hel l and annul ar p l a t e w e l d s u s in in g a n a p p r o p r i a t e p a i n t .

procedure 16.2.5 Changes affecting approval. A welding procedure

shallll b be e req requir uired ed when any of the t he chang changes es specified speci fied t e s t sha i n BS 4870 : Part 1 and/or the f oll owi ng are are mad made e to an approved welding procedure.

(a) A change of brand of hydrogen-controlled welding.

purchaser (see 3.2(n)). Otherwise, approved welders shall carry out ou t these these operations.

16.3.3 E x a m i n a t i o n o f welders'test plates. Each Each bu tt welded test-p tes t-plate late shall shall be radiograp radio graphed hed n accordance accordance with BS 4871 : Part 1.

16.3.4 E x t e n t o f approval. A wel welder der who has succes successsfu ll y weld welded ed the specifi specified ed e s t s shall be approved approved o the extent specified in BS 4871 : Part 1 except that: (a) a welder who w ho has successful successfully lyweld welded ed the tests using a basic coated electrode shall e approved to use rutile, cellulosic or iron powder coated electrodes; (b) a welder who has successfully welded the te s ts using a ru rutil til e coated electrode shall be approved approved to use cellucellu losic or iron powder coated electrodes;

(c) a ch chan ange ge from fro m single single arc t o mult iple arc or vice versa fo forr we.lde we.lders rs operating automatic autom atic or semi-automatic machines requires re-testing.

16.3.5 Records 16.3.5.1 Copies of the records of each welder's approval

electrode or in automati au tomatic c welding consumabl consumables, es, except except for fo r the wi wire re in submergedsubmerged-arc arc welds welds..

shalll be available shal available for examination examin ation on s i t e by the purchaser

(b) For a specif specified ied weld preparation i n plates plates 12.5 mm thick and thicker, a ch chan ange ge of more than -t- 25 % in the number of runs. I f the cross-sect cross-sectional ional area of the groove is increased, it i s permissible to increase the number of runs in propo p roportio rtion n t o the inc incre rease ase in area. area.

who o has been approved shall n ot be 16.3.5.2 A welder wh prevented preven ted from undertaking production work pen pendin ding g examination examin ation of these these rec records ords,, or certified copies copies of the these se records, provided 16.3.5.1 ha has s be been en comp c omplie lied d with.

(c) For automatic girthseam welding, a change from multiple runs per side to single run per side. (dl For automatic girthseam welding, a change from single single arct o multiple mult iple arc or vice-ver vice-versa. sa.

16.3 Approval process for welders 16.3.1 A p p r o v a l o f welders. Each welder shall be approved before welding on he tank. A welder who has successfully welded the procedure e s t plate shall b e considered to have

(see

17

3.4 d)).

Radiography

17.1 Application The procedure specified n this clause clause shall shall apply t o the inspection inspect ion of the joints listed in 17.3. Radiographic examination exami nation of fill et etwelds welds shall not be required.

17.2 Preparat Preparation ion for examination

been approved. tests. Each welder shall be approved n 16.3.2 Appr oval tests.

accordance accord ance wi th BS 4871 : Part 1 and this standard, except for the following applications. (a) Unl Unless ess specifically required by b y tthe he purchas purchaser er (see 3.2(m)), a welder who i s only required to ma make ke fil let le t welds welds on the tank tank bottom, roof or shell shell plates plates not no t exceeding 12.5 mm thickness, except for the shell-tobot tom we weld ld,, i s no t req required uired to t o pa pas ss an approval test, but his standard of workmanship shall be such that the requirements of this sta standar ndard d are maintained.

(b) Tack welding of shell, roof or bottom, where the tack weld shall be removed by gouging or shall be completely comple tely fused fused,, c can an be be carried out by non-approved operators who are are suitably sui tably instructe instructed d and and supervi supervised sed t o the purchase purchaser's r's satisfaction when permitted pe rmitted by the th e

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17.3.1 The extent of radiography shall be not less than that listed listed in table 6 for each plate thickness, but shall include one radiograph radiograph taken rom the fir st completed vertical joint for each welding process and thickness, if differing by more more than ? 3 mm, welded by b y each welder. welder. Thereafter, without regard to the number of welders working thereon, the same incidence of radiography shall be maintained. NOTE. T h e l o c a t i o n o f t h e r a d i o g r a p h s i s t o b e d e t e rm rm i n e d i n a g r e em em e n t w i t h t h e p u r c h a s e r .

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17.3 Extent of o f radiogr radiography aphy per per tank

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COPYRIGHT 2002; British Standards Institution on ERC Specs and Standards

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Surface dressing of butt-welded seams is not normally required. except hat surfac surface e irre irregulari gularities ties which may confuse or mask any objectionable defect shall be carefully removed.

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B S I BS*2b54

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BS2654:1989

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Table 6. Extent o f radiography per tank Thinner plate thickness

Vertical Verti cal welds andT-joints

Hor Horizo izonta ntall se seam ams s

Over 25 mm

10 % of to tota tall seam length plus all T-junctionst

2 %of s se eam length

10 % of to tota tall seam length,

2 % of seam length

Over Over 13 mm up t o and including 25 mm

Up to and including 13 mm

a t least half of the

Annular bottom buttwelds' buttwelds'

radiographs to include T-junctions 1 of total vertical seam length

Annular plates over 1O mm Annular plates over 8 mm up to and and including 1 10 0 mm Annular plates up to and including 8 mm

1 % of seam length All joints Half the numberof numberof joints A quarter of the number of joints, with a minimum of 4 radiographs

*The length to be radiographed shall consistof consistof that lengt length h from the outsi outside de of the annula annularr plate to a po int 250 mm inside the tank. t 5 0 % o f radi radiogra ographs phs wi th fil m horizontal and and 50 % of radi radiogra ographs phs wit h fil m verti vertical. cal.  

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17.3.2 Butt welds around the periphery of an insert plate  |   |   

shall be radiographed over the whole of their length length..  |   |     |   |   

NOTE, When two or more tanks are erected in the same location for the same same pur purcha chaser ser,, either ei ther co concu ncu rre rrently ntly or consecutively conse cutively,, the initial radiographs of the work of each welder need only be taken on one one tank, I n addition, the tot al number of radiographs taken may be based on the aggregate length of welds for the same type and thickness n suc such h a group of tanks rather than on the length in eac each h tank, b ut wi th a minimum of 50 % of the coverage requirements given n ttable able 6 on each tank.  |   |   |   |     |   |   |     |     |   |   

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17.4 Radiography procedure

subjected to t o mechanical or chemical damage and it i s particularly impor important tant to t o guard guard again against st inadvertent inadvertent exposure to sunlight, radiation or excessive heat. exposing, g, fil m propr o17.4.4 Standard test radiograph. The exposin

cessing and handling procedures shallbe shallbe demonstrated to the purchaser and s shall hall be subject subject t o his approval approv al (see 3.4 e)). A standard t e s t radiogr radiograph aph shall be prepared and shall be made available availablefor inspection. inspectio n.

17.4.5 Ima Image ge qualit y indicators. To check the degree of definition and contrast achieved and to determine whether the minimum mi nimum radiog radiographic raphic standard s being attained,