BSI Standards Publication

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1 BSI Standards Publication Shell boilers Part 4: Workmanship and construction of pressure parts of the boiler

2 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN :2018. It supersedes BS EN :2002, which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee PVE/2, Water Tube And Shell Boilers. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. The British Standards Institution 2018 Published by BSI Standards Limited 2018 ISBN ICS Compliance with a British Standard cannot confer immunity from legal obligations. This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 April Amendments/corrigenda issued since publication Date Text affected

3 EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM EN March 2018 BS EN :2018 ICS Supersedes EN :2002 English Version Shell boilers - Part 4: Workmanship and construction of pressure parts of the boiler Chaudières à tubes de fumée - Partie 4 : Fabrication et construction des parties sous pression des chaudières Großwasserraumkessel - Teil 4: Verarbeitung und Bauausführung für drucktragende Kesselteile This European Standard was approved by CEN on 6 December CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMITÉ EUROPÉEN DE NORMALISATION EUROPÄISCHES KOMITEE FÜR NORMUNG CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels 2018 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN national Members. Ref. No. EN :2018 E

4 Contents Page European foreword Scope Normative references Terms and definitions Symbols General requirements General Traceability General Material Welding Inspection (NDT) Cylindrical shells Tell-tale holes End plates and tube plates Plain tubes and stay tubes Manhole frames and openings Jointing flanges Openings for access and inspection Connections for accessories Accessories Set-in flange and set-on flange Flanges on nozzles Bolting Cylindrical furnaces Water-cooled reversal chamber Stays Bar stays Girder stays Tube stays Non-perpendicular bar stays or tube stays Design of welded joints Weld deposition Weld crosses Types of welds Weld preparations Welding plates of unequal thickness Openings in or adjacent to welds Fabrication General Welding Cutting, fitting and alignment Longitudinal seams Circumferential seams Surface condition before welding

5 Middle line alignments Surface alignment tolerances Miscellaneous welding requirements Repair of weld defects Post-weld heat treatment (PWHT) and other heat treatments General Material thickness Annex A (normative) Typical welds for shell boilers Annex B (informative) Gaskets for closing systems of access and inspection openings Annex C (informative) Significant technical changes between this European Standard and the previous edition Annex ZA (informative) Relationship between this European Standard and the Essential Requirements of EU Directive 2014/68/EU aimed to be covered Bibliography

6 European foreword This document (EN :2018) has been prepared by Technical Committee CEN/TC 269 Shell and water-tube boilers, the secretariat of which is held by DIN. This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by September 2018, and conflicting national standards shall be withdrawn at the latest by September Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN shall not be held responsible for identifying any or all such patent rights. This document supersedes EN :2002. This document has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirements of EU Directive(s). For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this document. The informative Annex C lists the significant technical changes between this European Standard and the previous edition. EN 12953, Shell boilers, consists of the following parts: Part 1: General; Part 2: Materials for pressure parts of boilers and accessories; Part 3: Design and calculation for pressure parts; Part 4: Workmanship and construction of pressure parts of the boiler; Part 5: Inspection during construction, documentation and marking of pressure parts of the boiler; Part 6: Requirements for equipment for the boiler; Part 7: Requirements for firing systems for liquid and gaseous fuels for the boilers; Part 8: Requirements for safeguards against excessive pressure; Part 9: Requirements for limiting devices of the boiler and accessories; Part 10: Requirements for feedwater and boiler water quality; Part 11: Acceptance tests; Part 12: Requirements for grate firing systems for solid fuels for the boiler; Part 13: Operating instructions; Part 14: Guideline for involvement of an inspection body independent of the manufacturer [CR ]. 4

7 Although these parts can be obtained separately, the parts are interdependent. As such, the design and manufacture of shell boilers requires the application of more than one part in order for the requirements of the standard to be satisfactorily fulfilled. NOTE A Boiler Helpdesk has been established in CEN/TC 269 which can be contacted for any questions regarding the application of the European Standards series EN and EN 12953, see the following website: According to the CEN-CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. 5

8 1 Scope This European Standard specifies requirements for the workmanship and construction of shell boilers as defined in EN NOTE 1 For other components such as water tube walls, see the EN series. NOTE 2 For economizers and superheaters, see EN or EN Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN :2007+A1:2013, Flanges and their joints Circular flanges for pipes, valves, fittings and accessories, PN designated Part 1: Steel flanges EN :1997, Flanges and their joints Circular flanges for pipes, valves, fittings and accessories, PN designated Part 2: Cast iron flanges EN :2009, Flanges and their joints Bolting Part 4: Selection of bolting for equipment subject to the Pressure Equipment Directive 97/23/EC EN :2004, Flanges and their joint Circular flanges for pipes, valves, fittings and accessories, Class designated Part 1: Steel flanges, NPS 1/2 to 24 EN :2013, Seamless steel tubes for pressure purposes Technical delivery conditions Part 2: Non-alloy and alloy steel tubes with specified elevated temperature properties EN :2002, Welded steel tubes for pressure purposes Technical delivery conditions Part 2: Electric welded non-alloy and alloy steel tubes with specified elevated temperature properties EN :2002, Welded steel tubes for pressure purposes Technical delivery conditions Part 5: Submerged arc welded non-alloy and alloy steel tubes with specified elevated temperature properties EN :2012, Shell boilers Part 1: General EN :2012, Shell boilers Part 2: Materials for pressure parts of boilers and accessories EN :2016, Shell boilers Part 3: Design and calculation for pressure parts EN :2002, Shell boilers Part 5: Inspection during construction, documentation and marking of pressure parts of the boiler EN ISO 2553:2013, Welding and allied processes Symbolic representation on drawings Welded joints (ISO 2553:2013) EN ISO :2017, Qualification testing of welders Fusion welding Part 1: Steels (ISO :2012 including Cor 1:2012 and Cor 2:2013) EN ISO 14731:2006, Welding coordination Tasks and responsibilities (ISO 14731:2006) EN ISO 14732:2013, Welding personnel Qualification testing of welding operators and weld setters for mechanized and automatic welding of metallic materials (ISO 14732:2013) 6

9 EN ISO :2004, Specification and qualification of welding procedures for metallic materials Welding procedure specification Part 1: Arc welding (ISO :2004) EN ISO :2017, Specification and qualification of welding procedures for metallic materials Welding procedure test Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys (ISO :2017) 3 Terms and definitions For the purposes of this document, the terms and definitions given in EN and the following apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: IEC Electropedia: available at ISO Online browsing platform: available at seam generic term for welded joints, welded seams or welds 4 Symbols For the purposes of this document, the symbols given in EN :2012, Table 1 apply. 5 General requirements 5.1 General The rules in this part are applicable to all aspects of fabrication, including welding, of boilers and boiler parts, and shall be used in conjunction with the specific requirements applicable to the grades of materials used All welding activities shall be in accordance with the requirements of this standard For category II, III and IV boilers, all welders or welding operators and welding procedures shall be approved (see ). For category I boilers, approval shall not be mandatory The manufacturer of a boiler, built in accordance with the requirements of this European Standard, shall be responsible for the welding done by his workmen or subcontracted by him. The manufacturer shall designate a competent welding supervisor in accordance with EN ISO No production work should be undertaken on category II, III and IV boilers according to the Pressure Equipment Directive PED 2014/68/EU until both the welding procedures and the welders or welding operators have been approved Materials and welding consumables shall fulfil the requirements of EN :

10 5.2 Traceability General The manufacturer shall demonstrate during the whole manufacturing process that identification and traceability shall be achieved for at least: pressure part materials; welding; inspection (NDT). This traceability shall be achieved through either marking of the part or by a documentation system Material Pressure bearing parts When laying out and cutting material the manufacturer shall take into consideration the location of the transferred identification markings to ensure that they are clearly visible when the pressure part is completed. In case the original identification markings are unavoidably cut out or the material is divided into two or more pieces the markings shall be accurately transferred by the manufacturer's nominated personnel prior to cutting. The actual material marking shall be by methods which are not harmful to the material in subsequent use/operation. The transfer of markings shall take place before partitioning of the product and after verification of the marks present with the corresponding certification. The manufacturer shall verify traceability of the material markings with the material certificates Non pressure bearing parts For non-pressure-bearing parts welded to a pressure part of the shell boiler, the material shall be compatible with the pressure part material, corresponding to a specification which can be identified, and shall have a maximum carbon content in the ladle analysis of 0,24 % Welding consumables The manufacturer shall ensure that the correct welding consumables according to the relevant welding procedure specification (WPS) are used Welding The welds made by each welder shall be marked with a stamp showing the welder s identity or some other appropriate record shall be made. If hand stamping is employed; only low-stress shall be used Inspection (NDT) An as built sketch or equivalent shall be produced by the manufacturer in order to record the locations where the NDT has been performed. On welds which have undergone RT or UT the zero datum point shall be indicated. The location of any repairs shall be also clearly indicated on the reports. 8

11 5.3 Cylindrical shells Each ring shall be formed from not more than two plates, bent to cylindrical form to the extreme ends of the plate. The bending shall be performed entirely by machine, and local heating or hammering shall not be used The shell of completed boilers shall be in accordance with the following requirements. a) Straightness Unless otherwise shown on the drawing, the maximum deviation of the shell from a straight line shall not exceed 0,3 % both of the total cylindrical length and of any 5 m length. Measurements shall be made to the surface of the parent plate and not to a weld, fitting, or other raised part. b) Irregularities in profile 1) Gradual local departures from circularity Irregularities in profile (checked by a 20 gauge) shall not exceed 2 % of the gauge length. This maximum value may be increased by 25 % if the length of the irregularities does not exceed one quarter of the length of the shell part between two circumferential seams, with a maximum of 1 m. Greater irregularities require proof by calculation or strain gauge measurement that the stresses are permissible. 2) Peaking at welded seams If an irregularity in profile occurs at the welded seam and is associated with flats adjacent to the weld, the irregularity in profile or peaking shall not exceed the values given in Table 1. Table 1 Maximum permitted peaking for dynamic and cyclic loads Dimensions in millimetres Wall thickness e Maximum permitted peaking e < 3 1,5 3 e 6 2,5 6 e 9 3,0 9 e the lesser of e/3, or 10 mm A conservative method of measurement (covering peaking and ovality) shall be by means of a 20 profile gauge or template. The use of such a profile gauge shall be in accordance with Figure 1. Two readings shall be taken, P 1 and P 2, on each side of the seam at any particular location, the peaking is taken as being equivalent to 0,25 (P 1 +P 2 ), or P 3. 9

12 a) 20 profile gauge b) Reading 1 c) Reading 2 d) Negative peaking (flat) Key a cut out in gauge to clear weld reinforcement Figure 1 Profile gauge and its method of use c) Out of roundness Out of roundness u shall be calculated in accordance with the following Formula (1): where ˇ 2 d ˆ d u = 100 in % (1) d ˆ + d ˆ d d is the maximum mean diameter of the shell; is the minimum mean diameter of the shell. The out of roundness u shall be 1,5 % for the concerned parts of the shell boiler except for corrugated furnace. 10

13 Measurements shall be made to the surface of the parent plate and not to the weld, fitting or other raised part. As example, shell sections should be measured for departure from circularity either when laid flat on their sides or when set up on end. If the shell sections are checked when laid flat, each measurement for diameter shall be repeated after turning the shell through 90 about its longitudinal axis. The two measurements for each diameter shall be averaged to give the out-of-roundness. Any local departure from circularity shall be gradual. d) Cold rolling Cold rolling of a welded shell to rectify a small departure from circularity shall be permitted, provided that non-destructive testing in accordance with EN is carried out after the departure from circularity has been remedied. 5.4 Tell-tale holes Reinforcing plates and saddles of nozzles attached to the outside of a boiler shall be provided with at least one tell-tale hole. These tell-tale holes may be left open or may be plugged when the boiler is in service. If the holes are plugged, the plugging material used shall not be capable of sustaining pressure between the reinforcing plate and the boiler wall. 5.5 End plates and tube plates If practicable, flat or dished ends shall be made in one piece except that, where the diameter is so large as to make this impracticable, flat ends may be made from two plates butt welded together (see Figure A1 in Table A.1). The weld shall be located preferably between two rows of bar stays or, if there is only one row of bar stays, between this row and the top row of stay tubes. Dished end plates and flanging of flat end plates shall be produced either by pressing or spinning. The cylindrical skirt shall have a good surface condition and shall be free from local irregularities. Cold forming of flat flanged end plates, tube plates and dished ends shall be permitted in accordance with an agreed approved procedure, including normalizing, if required. Hot forming of plates that have been dished or flanged at non-uniform temperatures, or that have been locally heated, shall be normalized after forming unless the manufacturer can demonstrate that the safety of the component is not affected. Where hemispherical shell end plates are pressed from one plate, they shall be pressed to form by machine in progressive stages, and shall be normalized on completion. Normalizing can be omitted for hot formed ends, when the forming process is completed at temperatures within the normalizing range. 5.6 Plain tubes and stay tubes Tubes shall be expanded or welded into the tube plate, or secured by a combination of both methods If the tubes are fully expanded only, the process shall be carried out with roller expanders, and the expanded portion of the tube shall be parallel throughout the full thickness of the plate In addition to expanded tubes, flared tubes, bell-mouthed tubes or beaded tubes shall be permitted Connections of smoke tube to tube sheet shall fulfil the requirements of EN :2016,

14 5.7 Manhole frames and openings Jointing flanges The jointing flanges of openings and covers shall be machined on the face and edges and on the bearing surface of the bolt heads and nuts Openings for access and inspection The closing system consists of the following elements: gasket; metallic closure parts with straight or conical welding rings; plain or dished cover; studs, nuts, washers and cross-bars. Recommendations for gaskets that are used for access and inspection openings are indicated in Annex B. The inboard cover is braced by studs, nuts and cross-bars and additionally acts self-sealing under internal pressure. In general, the joint surfaces shall be machined. a) b) c) d) Figure 2 Typical types of closing systems for access and inspection openings Openings for access and inspection shall fulfil at least the requirements of this European Standard and the following: a) Covers shall be formed to fit closely to the internal joint surface and shall be fitted with studs, nuts and cross bars; b) The spigot part, or recess of manhole and sight-hole covers (i.e. headholes and handholes) shall be as neat a fit as practicable. However, in no case shall the clearance b all round exceed 2 mm (see Figure 3); c) Ring and cover shall be chosen in such a way that the cover does not clamp and the gasket is laid on the sealing surface in a proper way; d) Tolerance of sealing surfaces: The deviation of the parallelism of the sealing surfaces in unbraced condition shall not exceed 1 mm for manholes or 0,5 mm for head- and handholes; e) The angle α between the sealing surfaces shall not exceed 2 in braced condition. The angle γ between ring and dished cover shall not exceed 20 (see Figure 3); f) Nuts shall be compatible with the studs; 12

15 g) The manufacturer of the gasket shall define the minimum required torque due to the geometry of the screws. The manufacturer of the closing system shall design the parts of the closing system in such way that the required minimum gasket load is reached. The permitted torque range shall be defined by the manufacturer of the closing system; h) The cross bars shall be designed for the maximum screw forces; i) Rough radial surface imperfections like corrosion scars, mechanical damages or erosion are not allowed; j) The use of type-tested gaskets is recommended. 5.8 Connections for accessories Accessories Figure 3 Opening for access and inspection Safety and pressure accessories shall not be attached directly to any boiler plate but through suitable forged, cast or fabricated nozzles. Screwed accessories shall not exceed DN 80 bore Set-in flange and set-on flange Set-in flange and set-on flange welded to the boiler shall be formed to fit closely to the plate to which they are to be attached (see Figure 7). If pads are used, the jointing surfaces shall be machined. The pads shall have sufficient thickness to allow the drilling of the stud holes for mountings without the inner surface being pierced and the length of the screwed portion of the stud in the pad shall be not less than the diameter of the stud Flanges on nozzles When nozzles are used, the flanges shall be in accordance with EN , EN or EN Flanges machined or thermal-cut by machine on the edges are accepted provided they satisfy with the requirements of this standard. The flange and bolting shall be calculated to withstand the design pressure and temperature, therefore the pressure-temperature rating tables of EN , EN and EN may be used. The flanges shall be machined on the jointing and if applicable on the bolting surfaces. 13

16 5.8.4 Bolting Bolting shall be in accordance with EN Cylindrical furnaces Each section of a cylindrical or conical furnace shall be made from a plate or from a tube. Furnace section shall be made from one plate. If this is not possible, no more than two plates shall be used for the concerned section; in this case the longitudinal welds shall be at least 120 apart and shall be full penetration butt welds in accordance with Alternatively, furnaces shall be made from tubes in accordance with EN , EN or EN Finished plain or corrugated furnace tubes shall be subjected to inspection, as follows: Visual (especially the welds and weld-adjacent zones); Dimensional according to and Table 2; NDT in accordance with EN For plain furnaces, the manufacturing tolerance on diameter shall be ± 5 mm. For corrugated furnaces, the manufacturing tolerance shall be as given in Table 2. Out of roundness (see c)), shall not exceed 1 % for corrugated furnaces or 1,5 % for plain furnaces. Any departure from circularity shall be gradual. Table 2 Manufacturing tolerances for corrugated parts of furnaces Symbol Definition Tolerance [mm] 50/150 and 75/200 (w/p cor ) d i Internal diameter of corrugation e Wall thickness after forming +4 0 L cor Total length of corrugations ±25 P cor Pitch of corrugations +2 5 w u Nominal depth of corrugations First and last 3 waves Out of roundness (see EN :2016, 13.3) Deviation from the straight line +10 / / 5 1 % 0,3 % of L cor The ordered wall thickness of the furnace (nominal thickness) shall not exceed the maximum allowable calculation thickness e fa in EN :2016, Clause

17 The ordered base materials (e.g. plates) shall take into account the manufacturing requirements to reach the ordered wall thickness of the corrugated furnace (finished product). For furnace wall thickness of 22 mm, the tolerances mentioned in Table 2 are acceptable. From the specified tolerance band may be deviated if the specific values (of the second moment of area I and of cross section area A with the measured thicknesses and the furnace) used for the calculation are verified separately. Key d i e w L cor P cor internal diameter of corrugation wall thickness after forming nominal depth of corrugations total length of corrugations pitch of corrugations Figure 4 Corrugated furnaces For special corrugations not specified in Table 2, the tolerances shall be agreed between the purchaser and the furnace supplier. These tolerances shall be considered during the design The longitudinal welds of furnaces shall be placed in such a position that they can be examined from the water side in accordance with access and inspection openings in accordance with EN :2016, Clause Corrugated furnaces and bowling hoops shall be produced by machine. They shall be normalized unless the manufacturing process is carried out above the normalizing temperature If stiffeners are required, they shall be attached externally by continuous full penetration welds During the assembly the gap between the furnace and front tube plate, rear plate and reversal chamber tube plate shall be nearly equal around the whole circumference. Furthermore, the edge shall be rounded or bevelled on gas inlet and outlet. Forms of furnace connections to front tube plate, rear plate and reversal chamber tube plate are shown in Figure 5. 15

18 Key a) Cold side 700 C b) Hot side > 700 C 1 The shape of the internal fillet weld should be concave, and be related to the shell thickness as follows: Minimum weld thickness of the back fillet weld: a 3 mm Instead of the fillet weld, welding with full penetration using ceramic protection backing or support is possible only if 100 % NDT is carried out (see EN :2002, Table 5.5-1) 2 Maximum value of 3 mm including weld 3 The plate edge radius of not less than e rf /2 is only required when the furnace end is exposed to flame or comparably high temperature g 1 as per WPS Figure 5 b) may also be used on cold side. Figure 5 Forms of furnace connections to front tube plate, rear plate and reversal chamber tube plate 5.10 Water-cooled reversal chamber The reversal chamber tube plates and end plates shall be welded to the wrapper plate, e.g. Figures D2 to D5 in Table A Stays Bar stays All bar stays shall be made from a solid rolled bar from only one section. If a stay is installed in position in the boiler, its axis shall be perpendicular normal to the plate which it supports. A tell-tale hole shall be drilled along the axis of all bar stays. The nominal diameter of the hole shall not exceed 5 mm and the drilling shall extend a minimum of 15 mm beyond the water surface of the plate. 16

19 Girder stays The attachment of girder stays welded directly to the crown plates shall be by means of full penetration welds Tube stays Tube stays shall be made from seamless or welded tube. If appropriate, tube stays can be fitted in accordance with the requirements of bar stays as given in Tube stays may be provided in two sections at least, provided the weld shall be full penetration and 100 % RT tested Non-perpendicular bar stays or tube stays Non-perpendicular bar stays or tube stays are only permitted for Low Pressure Boilers (LPB) (see EN :2012, 3.6). Stay tubes in a tube nest shall not be permitted Design of welded joints Weld deposition The design of the welded joints shall be such as to provide adequate access to enable the deposition of weld metal to meet the requirements laid down in this European Standard. The welds shall be full-penetration welded, where applicable, according to Annex A, and the weld preparation may be I-, Y- (HY), V (HV) or X (K). Other weld preparation is allowable if the equal level of safety is achieved. Welding procedure specification (WPS) shall be provided by the manufacturer showing the details such as bevelling. Butt-joints with a difference in thickness of more than 20 % or more than 3 mm the thicker plate shall be bevelled with an angle not exceeding 15 to the thickness of the thinner plate Weld crosses Pressure parts Joints shall not be permitted where more than two welded seams meet at one point. If a component is made of two or more shell sections, the longitudinal seams shall be completed before commencing the adjoining circumferential seam(s). The longitudinal seams of each adjacent section shall be staggered by at least 100 mm and they should, if possible, be located in a way to allow inspections Non-pressure parts For the attachment of non-pressure parts by welding the following designs shall be avoided: attachment welds crossing existing main welds; attachment welds where the distance between the edge of the weld and the edge of the existing main welds or nozzle welds is less than the minimum of twice the thickness of the pressure part or 40 mm. 17

20 If this is not possible, they shall cross the main weld perpendicular as far as possible and completely rather than stopping abruptly near the main or nozzle weld in order to avoid stress concentrations in these areas Types of welds Full penetration welds The following welds shall be of the full penetration type in accordance with Annex A (see Table A.1): a) longitudinal and circumferential main seams in cylindrical shells, furnaces and reversal chamber wrapper plates; b) seams in flat end plates; c) unflanged flat end plates or tube plates where they are welded: 1) to shells; 2) to furnaces; 3) to reversal chamber wrapper plates; and 4) to access tubes; d) attachment of flanged end plates; e) welds of branches, nozzles and pads (set-in flange and set-on flange) considered to be reinforcing (In case of reinforcing plates only the connection between nozzle and reinforcing plate shall be full penetrated); f) weld neck flanges to pipes; g) manhole frames, gusset stays, furnace stiffeners, and reversal chamber girder stay attachment welds Internal fillet welds (back welds) When unflanged flat end plates or tube plates are welded to shells, furnaces and reversal chamber wrapper plates, the internal fillet welds shall be deposited for the full circumference of the seam, except as permitted for small boilers in accordance with EN :2016, Table 6, water-walls of vertical boilers and electric boilers. The fillet welds shall be back welded where possible (accessibility for welding). Instead of the fillet weld, welding with full penetration using ceramic protection backing or support is possible only if 100 % NDT is carried out. The profile of the fillet welds shall be such as to minimize harmful notch effects. Welding procedure specification (WPS) shall be provided for both sections with or without back welded Other welds Welds other than full penetration welds shall be permitted for welding stay tubes to tube plates, plain tubes to tube plates, bar stays to tube plates, and fillet welds attaching compensating plates. 18

21 Weld preparations The dimensions and shape of the weld preparation as defined within the welding procedure specification (WPS) shall permit sound welds (see ) Welding plates of unequal thickness If plate edges of unequal thickness are abutted, and if the difference between the surfaces on either side exceeds that specified in , the thicker plate shall be trimmed to a smooth taper 15, including the width of the weld if so desired Openings in or adjacent to welds Openings in or adjacent to welded seams shall be avoided, especially if the seams are not stress relieved. Openings in or adjacent to welded seams shall be in accordance with EN : Fabrication General The weld shall be in accordance with the requirements of this standard and shall be supported by procedure qualification records (PQR) as well as welding procedure specification (WPS). This documentation shall be in accordance with If the welding is subcontracted, the manufacturer is responsible to approve all relevant documentation related to welding provided by the subcontractor Welding General Any process shall be acceptable provided that it meets the requirements of the approved welding procedures Welding procedure specification (WPS) The manufacturer shall provide the corresponding welding procedure specification (WPS) for each weld in accordance with EN ISO The manufacturer shall also provide WPS in order to perform the corresponding procedure qualification records Procedure qualification records (PQR) The manufacturer shall provide the corresponding procedure qualification records (PQR) supporting the welding procedure specification (WPS) in accordance with EN ISO , if relevant, including post-weld heat treatment Welding consumables Electrodes, filler wires, filler rods, fluxes, fusible inserts, shielding and purge gases shall either: a) comply with the relevant European Standards; or b) where relevant European Standards do not exist, comply with the relevant national standards. The manufacturer shall ensure that the correct consumables, as stated in the welding procedure specification (WPS), shall be used during manufacturing operations. All consumables including gases shall be stored and handled with care, and used in accordance with the conditions specified by the consumable manufacturer. 19

22 Electrodes, filler wires, filler rods and fusible inserts that show signs of damage or deterioration, such as cracked or flaked coatings or rusting or dirty electrode wire, shall not be used. Fluxes shall be clean and dry Welders and welding operators The list of welders and/or welding operators who have been involved in the manufacturing process of a shell boiler shall be registered by the manufacturer in order to demonstrate the traceability of each weld. The welders shall be approved in accordance with EN ISO :2017 for the intended processes, material groups and range of sizes and shall be in possession of a valid test certificate in accordance with EN ISO :2017, Annex A. Welding operators for fully mechanized or automatic processes shall be approved in accordance with EN ISO For pressure equipment, permanent joints in categories II, III and IV, the route 9.3 c) according to EN ISO and route 5.3 c) according to EN ISO is not permitted Temporary attachments Temporary attachments welded to the pressure parts shall be kept to a practical minimum. Temporary attachments (except hydraulic testing blanks) shall be removed prior to the first pressurization unless they have been designed to the same requirements as permanent attachments. The removal technique shall be such so as to avoid, as far as practicable, impairing the integrity of the pressure part and shall be by chipping, grinding or thermal cutting followed by chipping or grinding. Any rectification necessary by welding of damaged regions after removal of attachments shall be undertaken by approved welders working to an approved welding procedure specification. All temporary attachments shall be removed. For removal the technique used shall be such as to avoid impairing the pressure part proper. The associated weld area shall be ground flush and examined, if relevant, by a surface flaw detection method appropriate to the material. If temporary attachments have not been designed to the same standard as permanent attachments, they shall be removed prior to the first pressure test. The preheating requirements, if applicable, shall be applied and maintained during tack welding and the welding of bridge pieces or other attachments. Filler materials used for tack welding shall be of a designation appropriate to the particular weld and shall be deposited in accordance with a welding procedure specification (WPS). Particular attention shall be paid to the quality of tack welds which shall be deposited by approved welders. Where necessary, the ends of these tack welds shall be dressed by grinding or chipping to facilitate proper fusion if they are to be incorporated into the root run. Any cracked tack welds shall be completely removed Stray arcing While arc strikes are to be avoided, any accidental arc strikes shall be ground smooth and the parent material examined, if necessary, by a surface flaw detection method appropriate to the materials Cutting, fitting and alignment Plates shall be cut to size and shape by thermal cutting, machining and/or any other adequate process. For plates not thicker than 15 mm, cold shearing can be used provided that the edges are examined (visually or otherwise) and found suitable for welding Thermal cutting of plate, sections, bars and forgings shall be at an ambient temperature greater than 5 C. 20

23 Plates shall be fitted, aligned and retained in position during welding. Bars, jacks, clamps, tack welds, or other appropriate means shall be used to hold the edges to be welded in line. Tack welds shall be removed unless they are completely fused into the weld. The edges of butt joints shall be held during welding so that the tolerances in and are not exceeded in the completed joint Longitudinal seams Longitudinal seams in shells shall be welded from both sides Circumferential seams If circumferential seams in shells are welded from one side only with the use of a backing strip, this backing strip shall be removed after welding and prior to any required non-destructive examinations, and it shall be of a material that will not adversely influence the weld Surface condition before welding The surface to be welded shall be clean and free from foreign material, such as grease, oil, lubricants and marking paints, for a distance of at least 25 mm from the welding edge. Detrimental oxide shall be removed from the weld contact area. If weld metal is to be deposited over a previously welded surface, all slag shall be removed to prevent inclusion in the weld metal Middle line alignments For longitudinal seams, the middle lines of the plates shall be in accordance with Table 3 and Figure 6. However, the limits for the alignments of the mid-lines may be exceeded if the design requires that the mid-lines be offset for some technical reasons, and these offsets shall be taken into account in the calculations. Table 3 Maximum misalignment for finished longitudinal seam in plates Thinner plate thickness e mm Maximum misalignment d 1 mm e 10 1 e > 10 e/10 21

24 a) b) c) Figure 6 Plate alignment Surface alignment tolerances Circumferential joints The maximum misalignment at the surface of the plates (see Figure 6) shall be as given in Table 4. If this misalignment would otherwise be exceeded, the surface of the thicker plate shall be tapered in accordance with Figures A2 and A3 in Table A.1. Table 4 Maximum misalignment of plates with circumferential joints Thinner plate thickness e mm Maximum misalignment d 2 or d' 2 mm e 20 e/4 e > Longitudinal joints The maximum misalignment at the surface of the plates (see Figure 6) shall be as given in Table 5. If this misalignment would otherwise be exceeded, the surface of the thicker plate shall be tapered in accordance with Figures A2 and A3 in Table A.1. 22

25 Table 5 Maximum misalignment of plates with longitudinal joints Thinner plate thickness e mm Maximum misalignment d 2 or d' 2 mm Miscellaneous welding requirements Double-sided welds e 12 e/4 e > 12 3 Depending on the welding method applied, the reverse side of double-sided welded joints shall be cleaned back to sound metal before applying weld metal from the reverse side Restart If the welding is stopped for any reason, extra care shall be taken on restarting to obtain the required penetration and fusion. For submerged arc welding, chipping out the groove in the crater is recommended Single-sided welds Where single-sided welded joints are used, particular care shall be taken to ensure complete penetration and fusion at the bottom of the joint for its full length End plates welded prior to hot or cold forming Hot forming of welded plates shall be permitted provided that the welded joint is subjected to 100 % volumetric examination after hot forming. Cold forming of welded plates shall be allowed under the following conditions: a) Forming precautions: Before cold forming, the weld reinforcement shall be ground smooth, and the manufacturer shall take precautions, where necessary, in order to avoid crack formation in the weld metal or the heataffected zone; b) Limiting thicknesses: The limiting thicknesses shall be 20 mm unless forming procedure qualification demonstrates that this limit can be exceeded; c) Forming: If the inside radius of curvature after forming is less than 10 times the thickness, an appropriate post forming heat treatment shall be applied; d) Control: After cold forming, the welded joints shall be visually examined and subjected, to 100 % volumetric examination throughout their length. Joints of any thickness which have been cold formed to an inside radius less than that specified in c) shall be inspected for cracks by magnetic particle or penetrant methods or by other agreed methods. 23

26 Permanent attachments Lugs, brackets, stiffeners, and other attachments shall fit to the curvature of the shell or other surface to which they are to be attached. All attachments to the pressure bearing parts should be welded before hydrostatic pressure test. If not practical, special arrangements should be provided (e.g. NDT) Repair of weld defects Any repair to a weld shall be recorded. The manufacturer, after due consideration of the importance and number of defects to be removed shall decide whether to carry out a number of local repairs, or whether to produce a new complete joint after grinding of the weld concerned. The welding procedure specification (WPS) for local or complete repairs shall be approved, if the welding procedure applied for repairing the defect is not the same. In the case of recurring unacceptable imperfections, the cause shall be determined and corrective action taken, all of which shall be recorded Post-weld heat treatment (PWHT) and other heat treatments General Post-weld heat treatment (PWHT) shall be performed provided material thicknesses of both welded parts are above 35 mm. In case that post-weld heat treatment (PWHT) needs to be performed, the appropriate procedure shall be written, for example based on EN The procedure qualification records (PQR) shall be provided Material thickness If a welded joint connects parts of different thickness, the thicknesses to be considered in applying the limits given in shall be the following nominal thicknesses, including corrosion allowance (see Figure 7): 24

27 Key 1 nozzle (set in) 6 pad (Set-in flange) 2 flange 7 pad (Set-on flange) 3 nozzle (set on) 8 manhole frame 4 reinforcing plate (compensation plate) 9 flat plate 5 non-pressure part NOTE For set-in flange and set-on flange, see Figure 7 Thickness to be considered when determining the requirement for post weld heat treatment a) the thickness of the shell or flat plate, as appropriate, in nozzle or pad attachment welds (A); Thickness of a pad and/or reinforcing plate should not be added to the wall thickness (A). b) the thickness of the nozzle neck at the nozzle neck to flange welds, and set-on nozzle to shell or flat plate welds (B); c) the throat thickness of the weld at the point of attachment where a non-pressure part is welded to a pressure part (C); d) the thinner of two adjacent butt-welded plates, including dished end to shell connections (D); e) the thickness of the shell in connections to flat plates which are butt welded to the shell (E); 25

28 f) the thickness of flat plates where they are set into the shell (F). 26

29 Annex A (normative) Typical welds for shell boilers This Annex A specifies design requirements of welds to be applied for shell boilers. Used symbols for welded joints in Table A.1 are in accordance with EN ISO Table A.1 Typical welds for shell boilers Ref. Type of joints Design requirements A Boiler shell A1 A2 A3 A4 Where plates differing in thickness by 3 mm or more, the thicker plate shall be bevelled with an angle of maximum 15 to the thickness of the thinner plate. Where plates differing in thickness by 3 mm or more, the thicker plate shall be bevelled with an angle of min. 15 but not exceeding maximum 30 in total to the thickness of the thinner plate. A5 The internal fillet welds can be omitted, see

30 Ref. Type of joints Design requirements B End plates (made at least in two parts) See A1 to A3 C Furnace C1.1 See Figure 5. C1.2 C2 See A1 or A2 or A3 Longitudinal and circumferential welds C3 In case of unequal thicknesses, limited to: e rs2 e rs1 Min [0,3e rs1 ;4] e 2 e 1 Min[0,3e 1 ;4] C4 For reinforcement ring b 22 mm 1 Continuous full penetration weld C5 For reinforcement ring b > 22 mm a 22 mm 1 Continuous full penetration weld 28

31 Ref. Type of joints Design requirements C6 C7 With or without back welding D Reversal chamber D1 D2 See A1 to A3 D3 D4 D5 E Reversal chamber access tube E1 29

32 Ref. Type of joints Design requirements E2 F Gusset and girder stays F1 1 All round smooth with groove F2 1 All round smooth with groove G Smoke tubes See EN :2016, Table 8. H Stay bars and stay tubes See EN :2016, Figures 24 to 27. I Openings, branch welds and pads I1 I2 No reinforcement of the shell by the nozzle. For nozzles > DN 50, only if: - no external loads can occur, - not for safety valves, - not for steam outlet. I3 30

33 Ref. Type of joints Design requirements I4 I5 No reinforcement of the shell by the nozzle. For nozzles > DN 50, only if: - no external loads can occur, - not for safety valves, - not for steam outlet. J Flanges to tubes, flanges to nozzle and/or pipe to pipe, circular weld for stay tubes J1 J2 This connection is not recommended for use if cyclic loading is expected to occur. 31

34 Annex B (informative) Gaskets for closing systems of access and inspection openings This Annex B specifies the recommendations for gaskets that are used for access and inspection openings according to of this standard. The gaskets used can be formed gaskets or endless gaskets. Gaskets should be suitable for the intended operation conditions (pressure and temperature). Other essential properties are: dimensional stability; chemical resistance against boiler water; durability. In general the use of sealing pastes or release agents is not allowed. Exceptions should be agreed with the gasket manufacturer. The suitability of gaskets can be verified, e.g. by a type examination. In general the service life of a gasket should reach a period between two internal recurrent inspections. Each gasket should be delivered with an operating manual, where the gasket manufacturer explicitly describes the installation of the gasket, the behaviour in operation (especially at boiler start-up) and maintenance. It should be pointed out to all safety-relevant aspects, particularly: allowable divergence from the parallelism of sealing surfaces; information for fixing the gasket at difficult installation conditions (e.g. overhead installation); remarks of boiler / closing system manufacturers; check of the gasket for proper condition and suitability for the use; quality of boiler water; centric installation of gasket; permissibility of use of sealing pastes or release agents; tighten of screws of the closing system according to the information of the indication of reference values for torque by manufacturer of closing system and of gasket, if applicable; limits for the minimum and maximum required surface pressure of the gasket; use of new gaskets after each opening of the closing system; service life of the gasket, when the closing system is not opened / cyclic loading / standstill periods; information about the check of gaskets and if applicable retorque of the screw joint of the closing system after putting the boiler into service up to 50 % of the allowable operating pressure PS; conditions of storage date of usability. 32