Recommendations for tube end welding Publication 143 Edition 2 Copyright © 2017 The Engineering Equipment and Materials Users Association. A company limited by guarantee. Registered in England. Company number 477838. All rights reserved. ISBN 978 0 85931 217 2 Imprint reference 02-2017 First published 02-2017 Registered and Trading Address: EEMUA, Second Floor, 16 Black Friars Lane, London EC4V 6EB Telephone: +44 (0)20 7488 0801 Email: sales@eemua.org Website: www.eemua.org EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Recommendations for tube end welding Publication 143 Contents Preface������������������������������������������������������������������������������������������������������������������������������������������������������������������ VII 1. Scope�������������������������������������������������������������������������������������������������������������������������������������������������������������������1 1.1 Acronyms and definitions......................................................................................................................................................................... 1 1.2 Convention........................................................................................................................................................................................................ 1 2. Welding process and joint detail����������������������������������������������������������������������������������������������������������������������3 2.1 Manual processes.......................................................................................................................................................................................... 3 2.2 Automatic and semi-automatic processes..................................................................................................................................... 3 2.3 Acceptable welding processes.............................................................................................................................................................. 3 2.4 Joint types.......................................................................................................................................................................................................... 3 2.4.1 Expansion only (no welding)....................................................................................................................................................... 3 2.4.2 Expansion and seal-welding........................................................................................................................................................ 4 2.4.3 External fillet weld............................................................................................................................................................................. 4 2.4.4 External butt and fillet weld......................................................................................................................................................... 5 2.4.5 Internal fillet weld.............................................................................................................................................................................. 5 2.4.6 Castellated.............................................................................................................................................................................................. 6 2.4.7 Full penetration internal butt weld.......................................................................................................................................... 6 3. Qualification of welding procedure������������������������������������������������������������������������������������������������������������������7 3.1 Introduction...................................................................................................................................................................................................... 7 3.2 Test samples..................................................................................................................................................................................................... 7 3.3 Non-destructive testing............................................................................................................................................................................. 7 3.3.1 Visual examination............................................................................................................................................................................ 7 3.3.2 Radiographic examination............................................................................................................................................................ 7 3.4 Destructive testing........................................................................................................................................................................................ 7 3.4.1 Weld strength tests........................................................................................................................................................................... 7 3.4.2 Macroexamination and hardness tests.................................................................................................................................. 8 3.4.3 Ferrite test.............................................................................................................................................................................................. 9 3.4.4 Corrosion test....................................................................................................................................................................................... 9 4. Qualification of welders and welding operators������������������������������������������������������������������������������������������ 11 4.1 Test samples...................................................................................................................................................................................................11 4.2 Test purpose...................................................................................................................................................................................................11 4.3 Previous qualification................................................................................................................................................................................11 4.4 Operators deemed competent............................................................................................................................................................11 IV EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding 5. Preparation of tubes and tube-plates����������������������������������������������������������������������������������������������������������� 13 5.1 Cleaning............................................................................................................................................................................................................13 5.2 Tube holes.......................................................................................................................................................................................................13 5.3 Assembly..........................................................................................................................................................................................................13 6. Tube location��������������������������������������������������������������������������������������������������������������������������������������������������� 15 6.1 Tube fit accuracy..........................................................................................................................................................................................15 6.2 Preparation for welding...........................................................................................................................................................................15 7. Preheat and interpass temperature�������������������������������������������������������������������������������������������������������������� 17 7.1 General...............................................................................................................................................................................................................17 7.2 Practical limits................................................................................................................................................................................................18 7.3 Weld interruption........................................................................................................................................................................................18 7.4 Preferred means of preheating............................................................................................................................................................18 8. Welding������������������������������������������������������������������������������������������������������������������������������������������������������������ 19 8.1 General...............................................................................................................................................................................................................19 8.2 Welding individually..................................................................................................................................................................................19 8.3 Distortion minimisation...........................................................................................................................................................................19 8.4 Autogenous welding.................................................................................................................................................................................19 8.5 Additional controls.....................................................................................................................................................................................19 9. Post-weld heat treatment������������������������������������������������������������������������������������������������������������������������������ 21 9.1 General...............................................................................................................................................................................................................21 9.2 Heating rates..................................................................................................................................................................................................21 9.3 Additional welding.....................................................................................................................................................................................21 10. Quality control and health and safety��������������������������������������������������������������������������������������������������������� 23 10.1 General............................................................................................................................................................................................................23 10.2 Samples..........................................................................................................................................................................................................23 10.3 Examination of materials......................................................................................................................................................................23 10.3.1 Tubes....................................................................................................................................................................................................23 10.3.2 Tube-plates.......................................................................................................................................................................................23 10.4 Health and Safety......................................................................................................................................................................................23 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association V Recommendations for tube end welding Publication 143 11. Cleaning and inspection������������������������������������������������������������������������������������������������������������������������������� 25 11.1 General............................................................................................................................................................................................................25 11.2 Dye penetrant testing............................................................................................................................................................................25 11.3 Other................................................................................................................................................................................................................25 12. Leak detection����������������������������������������������������������������������������������������������������������������������������������������������� 27 12.1 General............................................................................................................................................................................................................27 12.2 Air testing......................................................................................................................................................................................................27 12.3 Gas leak testing..........................................................................................................................................................................................27 12.4 Other leak testing......................................................................................................................................................................................27 12.5 Leak investigation.....................................................................................................................................................................................27 13. Repairs����������������������������������������������������������������������������������������������������������������������������������������������������������� 29 13.1 Leaks.................................................................................................................................................................................................................29 13.2 Qualified procedure.................................................................................................................................................................................29 13.3 Cause of defect...........................................................................................................................................................................................29 14. Tube expansion��������������������������������������������������������������������������������������������������������������������������������������������� 31 14.1 General............................................................................................................................................................................................................31 14.2 Location..........................................................................................................................................................................................................31 14.3 Equipment....................................................................................................................................................................................................31 14.4 Tube wall thinning...................................................................................................................................................................................31 14.5 Bores.................................................................................................................................................................................................................31 15. Pressure testing�������������������������������������������������������������������������������������������������������������������������������������������� 33 15.1 Cleaning.........................................................................................................................................................................................................33 15.2 Final acceptance pressure test..........................................................................................................................................................33 15.3 Leaks.................................................................................................................................................................................................................33 15.4 Repair...............................................................................................................................................................................................................33 16. Draining and dewatering����������������������������������������������������������������������������������������������������������������������������� 35 16.1 General............................................................................................................................................................................................................35 16.2 Heating...........................................................................................................................................................................................................35 17. Supervision and inspection�������������������������������������������������������������������������������������������������������������������������� 37 17.1 General............................................................................................................................................................................................................37 17.2 Inspection and Test Plan (ITP)............................................................................................................................................................37 VI EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding 18. Records���������������������������������������������������������������������������������������������������������������������������������������������������������� 39 References������������������������������������������������������������������������������������������������������������������������������������������������������������ 41 Figures Figure 1 Expansion only�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 3 Figure 2 Expansion and seal-welding���������������������������������������������������������������������������������������������������������������������������������������������������������������� 4 Figure 3 External fillet weld������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 4 Figure 4 External butt and fillet weld����������������������������������������������������������������������������������������������������������������������������������������������������������������� 5 Figure 5 Internal fillet weld�������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 5 Figure 6 Castellated������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������������ 6 Figure 7 Full penetration internal butt weld�������������������������������������������������������������������������������������������������������������������������������������������������� 6 Figure 8 Weld strength tests����������������������������������������������������������������������������������������������������������������������������������������������������������������������������������� 8 Tables Table 1 Preheat and interpass temperature������������������������������������������������������������������������������������������������������������������������������������������������ 17 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association VII Recommendations for tube end welding VIII EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 Preface Publication 143 was first published under the EEMUA banner in 1985 following the merger of the Engineering Equipment Users Association (EEUA) and the Oil Companies Materials Association (OCMA). The Publication was originally OCMA Specification No. TEW-1: Recommendations for tube end welding: tubular heat transfer equipment, Part 1 – Ferrous materials. It was written by OCMA’s Welding Panel with assistance from the Heat Transfer Society. In the interim, codes such as ASME BPVC VIII, ASME IX and particularly EN ISO 15614-8:2002 have covered much of the same ground. This new Second Edition of EEMUA 143 takes ISO 15614-8:2016 Specification and qualification of welding procedures for metallic materials Welding procedure test – Part 8: Welding of tubes to tube-plate joints as the primary source material with some additions where it was felt that the standard required further clarification, or does not address the topic sufficiently. A joint meeting was convened in October 1966 of members of OCMA welding panel and representatives of the Heat Transfer Society to exchange information on experience gained in making welded joints between heat exchanger tubes and tube-plates. It was the opinion of that meeting that an urgent need existed for standardised procedures to be established for the design, fabrication, inspection and testing of these and similar components. At that time, there was no national or international standard in existence that adequately covered this important subject. Members pooled their knowledge and experience, and co-operated in preparing a recommended practice for tube end welding and testing. Such a recommendation could then be used as a basis for specifying requirements for the oil, chemical and other industries. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association IX Recommendations for tube end welding X EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 1. Scope This Publication supplements the requirements of ISO 15614-8:2016 for all tube to tube-plate welding. However, it does not cover joints made purely by mechanical means, e.g. expansion. 1.1 Acronyms and definitions 1.2 Convention This Publication refers to parts of other specifications as ‘section’ and to its own contents as ‘clause’. The following list of acronyms used in this Publication are defined below: ANSI ASME ASTM AWS BPVC EN GTAW HAZ ID IEC IIS IIW ISO ITP NDT OD TEMA UTS American National Standards Institute American Society of Mechanical Engineers American Society for Testing and Materials American Welding Society Boiler and Pressure Vessels Code European Standards Gas Tungsten Arc Welding Heat Affected Zone Inside Diameter International Electro-technical Commission Italian Institute of Welding International Institute of Welding International Organization for Standardization Inspection and Test Plan Non Destructive Testing Outside Diameter Tubular Exchanger Manufacturers Association Ultimate Tensile Strength EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 1 Recommendations for tube end welding 2 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 2. Welding process and joint detail 2.1 Manual processes 2.4 Joint types Earlier editions of this Publication included detailed design criteria based on IIS/IIW recommendations that represented welding practice at that time, including details of suitable joint sizes relative to individual, mostly manual, welding processes. This level of detail is not included in this edition as the majority of welding will be automated. No joint types are prohibited but the main joint types can be summarised as follows: 2.2 Automatic and semiautomatic processes 2.4.1 Expansion only (no welding) Expansion-only joints are outwith this Publication and not usually permitted for process service due to the risk of crevice corrosion at the tube-totube-plate edge. Modern welding techniques for tube-to-tube-plate welding predominantly use automatic welding machines that are capable of consistent results and can accurately reproduce the weld joints performed during qualification testing. However, it is still sometimes necessary to use manual or semi-automatic processes, particularly in the case of large diameter tubes. 2.3 Acceptable welding processes Figure 1 Expansion only All welding processes are permissible, provided that acceptable results and appropriate metallurgical properties can be achieved during procedure qualification and reproduced consistently in production. This Publication does not prohibit the use of any suitable welding process. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 3 Recommendations for tube end welding Publication 143 2.4.2 Expansion and seal-welding 2.4.3 External fillet weld For certain applications, and where specified in the Purchase Order, expansion into ring groove(s), coupled with seal-welding may be utilised. This method introduces risks if the tube is fully expanded prior to welding as gases evolved/ released during welding will not be able to escape from the root side of the joint. Therefore, partial expansion to secure the tube, followed by welding and final expansion is recommended. The tube passes completely through and extends beyond the tube-plate, allowing a fillet weld to be performed on the outside diameter of the tube. The fillet leg size can exceed the tube wall thickness and is normally specified as 1.4t minimum to provide a weld throat thickness at least equal to the tube wall thickness. This method is recommended for manual and semi-automatic welding processes. When this method is applied, all criteria of this Publication and ISO 15614-8 apply with the exception of the 0.9t weld throat requirement. L t Figure 2 Expansion and seal-welding Figure 3 External fillet weld 4 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Recommendations for tube end welding Publication 143 2.4.4 External butt and fillet weld 2.4.5 Internal fillet weld This configuration is similar to the external fillet weld, but a bevel is cut into the tube-plate allowing the resulting butt weld throat to be supplemented by the fillet weld. The advantage of this design is that the overall weld volume is reduced and there is less chance of burning through the tube wall. Internal fillet welds are commonly applied using manual, semi-automatic, or automatic welding processes. There is a risk of inadequate weld throat thickness as the fillet leg length cannot exceed the tube wall thickness. As a result of this ISO 15614-8 table 4 item 16 has a weld throat acceptance criterion for the macrosections of 0.9t instead of the 1t that would be expected for a full strength joint. There is a risk of lack of fusion at the weld root on the tube-plate due to the larger wall thickness, particularly for manual and semi-automatic welding. t L tb Push-through tensile tests are more likely to fail in the weld as a result of this reduced throat thickness (see clause 3.4 Weld Strength Tests). There is an additional risk of excessive weld penetration into the tube ID when using this joint configuration and trying to obtain sufficient weld throat thickness. t a = t b + 0.7L a Figure 4 External butt and fillet weld Figure 5 Internal fillet weld EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 5 Recommendations for tube end welding Publication 143 2.4.6 Castellated 2.4.7 Full penetration internal butt weld A U-Groove is machined into the tube-plate to provide a joint that appears to be a concentric tube outside the tube. The advantage of this configuration is that the heat sink on the tube-plate side is reduced to be comparable with the tube. Furthermore, welding distortion of the tube-plate is minimised. A U-Groove is machined into the tube-plate to provide a joint that appears to be a matching tube on the tube side of the tube-plate. This allows a full penetration weld to be performed from the inside of the tube and will normally require an additional shielding gas to be applied from the outside of the tube. The preferred geometry on the right includes a recess that centres the tube and provides additional weld metal for autogenous welds (though see clause 8.4 of this Publication). A disadvantage of this joint configuration is that the weld bead profile becomes critical to achieving sufficient weld throat. t D W Although this configuration is shown without a root gap, a gap can be incorporated to allow filler metal addition by fed wire or consumable insert ring. This specialist geometry is employed to eliminate crevices on both side of the tube-plate, particularly for liquid/liquid heat exchangers. It is also the only joint type that permits full volumetric NDT. t <= D <= 2t W=t Figure 6 Castellated Figure 7 Full penetration internal butt weld 6 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Recommendations for tube end welding Publication 143 3. Qualification of welding procedure 3.1 Introduction 3.3 Non-destructive testing Qualification of weld procedures should be in accordance with ISO 15614-8 as modified by this Publication. 3.3.1 Visual examination The Purchaser shall be given sufficient notice to enable them or their representative to witness all weld procedure qualification tests. At the discretion of the Purchaser, the results of previously 3rd party-authenticated procedure tests may be acceptable. A visual examination of the welds shall show uniform contour without excessive reinforcement with the bores of the tubes free from any spatter, obstruction, weld spillage or overfill, which is considered to be detrimental. 3.3.2 Radiographic examination Refer to ISO 15614-8 Section 8.1.4. 3.4 Destructive testing 3.2 Test samples All tubes used for procedure testing shall be of the same diameter, wall thickness and nominal chemical composition as those proposed for production. Tube-plate material to be used for the procedure test shall also be of the same nominal composition and supply condition (including product form and heat treatment) as that to be used in manufacture. Qualification range shall be in accordance with ISO 15614-8 Table 5 (section 9.3.2), except as follows: • When the thickness of the tube-plate (t2) is less than 35mm, the qualified thickness range is 0.75t2 – 1.5t2; • The tube nominal diameter and wall thickness for mechanised / automatic welding shall be the size used for qualification; 3.4.1 Weld strength tests Unless otherwise specified by the Purchaser, three tensile tests shall be carried out in accordance with ISO 15614-8, Section 8.1.7, as amended below. Note that for larger diameter tubes (over 40mm) this means that the minimum number of tubes to be welded is eight. The purpose of the tensile test is to apply a tension load to the tube and weld. This can be carried out by direct tension test on the tube end or by pushing a plunger through the welded end of the tube against the closed end, as shown in the following figures. The breaking load should then be recorded. If tube expansion after welding is specified, it may be necessary for a sample of full plate thickness to be employed (see clause 14 of this Publication). EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 7 MACHINED HIGH TENSILE ROD (SLIP FIT IN TUBE BORE) Recommendations for tube end welding MACHINED PLUG Publication 143 SUPPORT RING d d BED PLATE LOAD IS APPLIED SLOWLY TO ENSURE NO SHOCK LOADING IS APPLIED AND TEST CONTINUED UNTIL FAILURE OF TUBE OR WELD RESULTS Alternative Testing Arrangements The results of the tension test shall comply with one of the following: 50 mm x 50 mm x 25 mm WITH TEST WELDS AT EACH END TENSILE M/C GRIPS 3.4.2 Macroexamination and hardness tests RECOMMENDED ALTERNATIVE Sections shall be cut, polished, and etched according to ISO 15614-8 section 8.1.5 FORCE APPLIED BY TENSILE TESTING M/C The transverse sections of welds, including weld craters, shall be free from cracks, fissures and lack of fusion. Slag inclusions and gross porosity shall not exceed the limits of ISO 15614-8 Tables 2 and 3. MACHINED HIGH TENSILE ROD (SLIP FIT IN TUBE BORE) MACHINED PLUG SUPPORT RING d d BED PLATE LOAD IS APPLIED SLOWLY TO ENSURE NO SHOCK LOADING IS APPLIED AND TEST CONTINUED UNTIL FAILURE OF TUBE OR WELD RESULTS Figure 8 Weld strength tests TENSILE M/C GRIPS 8 • Failure in the tube is acceptable. • Failure in the weld or heat affected zone at or above 100% of specified minimum UTS of the tube material is acceptable. • Another criterion as agreed between Purchaser and Manufacturer, e.g. for a partial strength weld. After polishing and etching the sections, the minimum throat thickness or leak path of each weld shall be not less than 0.9t1, where t1 is the nominal wall thickness of the tube. The size of any visible imperfections shall be taken into account in assessing the dimensions of the minimum leak path. Hardness tests shall be carried out in accordance with ISO 15614-8 section 8.1.6 for all materials. Acceptance criteria for metals that do not have a specified maximum in EN ISO 15614-1 shall be as-specified for the base material specification or as agreed between the Purchaser and Manufacturer. The Purchaser may specify additional limits based on application requirements. 50 mm x 50 mm x 25 mm WITH TEST WELDS AT EACH END EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Recommendations for tube end welding Publication 143 3.4.3 Ferrite test For duplex and super duplex austenitic / ferritic stainless steels two faces 90°apart shall be polished to a one micron finish and suitably etched. The specimen shall be examined for any deleterious third phases and ferrite content shall be determined using point counting to ASTM E562. The acceptance criterion shall be 35% - 65% ferrite in the weld and HAZ. Note: For tube-plates in the vertical position, the ferrite determination shall be carried out at 3 and 12 o’clock positions. For tube-plates in the flat position, two diametrically opposed tests are required. 3.4.4 Corrosion test For duplex austenitic / ferritic and superaustenitic stainless steels, a corrosion test shall be carried out in accordance with ASTM G48. Care should be taken to grind away or seal crevices on the root side, depending on weld geometry. The minimum test parameters and acceptance criteria shall be as follows: 22% Cr duplex 25% Cr duplex 27% Cr duplex 6% Mo 24hrs @ 22° C minimum 24hrs @ 35° C minimum 24hrs @ 40° C minimum 24hrs @ 35° C minimum The acceptance criteria shall be a weight loss < 4g/m² and no pitting on the test face. If the weight loss is >4g/m² and it can be positively identified that this is only due to corrosion at the cut faces, the test shall be invalid. In this case re-testing shall be carried out on replacement specimens. For other corrosion-resistant alloys, test requirements will be defined by the Purchaser. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 9 Recommendations for tube end welding 10 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 4. Qualification of welders and welding operators 4.1 Test samples Every welder or welding operator shall be required to produce evidence of his ability by making a test sample similar to that prescribed for welding procedure qualification in clause 3. A minimum of 3 tubes shall be welded by the welder/operator. One of these tubes shall be used to obtain two macro-sections 90°apart (12 and 3 o’clock if tube-plate vertical). Unless otherwise specified by the Purchaser, the two remaining tubes should be subjected to tension tests in accordance with clause 3.4. 4.4 Operators deemed competent A welder/operator who welds test pieces that meet the requirements of clause 3 is deemed to qualify for production welding. Tests shall comply with the same acceptance criteria as the weld procedure test. 4.2 Test purpose The purpose of this qualification test is to demonstrate that both the welders and welding equipment are capable of producing satisfactory joints in accordance with the approved weld procedure (See clause 10.1). The Purchaser shall be given sufficient notice to enable them or their representative to witness all welder/welding operator qualification tests. 4.3 Previous qualification Welders/operators who have been previously qualified within the last six months or who are currently working on similar materials using similar techniques may be acceptable without further qualification (See clause 18). EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 11 Recommendations for tube end welding 12 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 5. Preparation of tubes and tube-plates 5.1 Cleaning 5.3 Assembly The ends of the tubes which are to be welded shall be cleaned and degreased with a suitable non-residue forming solvent, both inside and out, for a length equal to the tube-plate thickness but not less than 25mm. It is recommended that the solvent used for degreasing materials should be chloride free, e.g. acetone. For welding with the GTAW process, the outside ends of the tubes for a minimum distance of 13mm shall be finished to bright metal, e.g. by linishing or power brushing. Tubes with score marks or any other surface irregularities at the ends shall not be used if considered to be detrimental to the production of sound welds. The face of the tube-plate, the holes and the tubes shall be free from dirt, grease, scale and other foreign matter when they are assembled. To avoid possible damage during assembly or entrapment of contaminants, baffle and support plate holes should be free from burrs and effectively cleaned prior to the commencement of tube insertion. 5.2 Tube holes The tube-plates shall be machined and the tube holes bored or drilled as required by the design. The holes so formed shall be normal to the tubeplate surface, parallel, circular and shall have smooth internal surfaces. They shall be free from burrs and, with the exception of the detail shown in 2.4.7, the shell side edges of the tube holes shall be chamfered or radiused to 1.5mm approx. It is recommended that the limits of tolerance of tube holes shall not exceed those defined by TEMA. Immediately prior to assembly, the plates shall be thoroughly cleaned and degreased using a nonresidue forming solvent. It is recommended that the solvent used should be chloride free, e.g. acetone. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 13 Recommendations for tube end welding 14 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 6. Tube location 6.1 Tube fit accuracy An accurate fit-up and intimate contact between the tube extremity and tube-plate is required. To achieve this, the tube end may be flared slightly by means of a clean dry tapered drift or punch. Alternatively, when it is required to move the assembly prior to welding, a light roller expansion to a maximum depth of 40mm is permissible. Such expansion may cause difficulties during welding and for this reason, it is not recommended. To minimise attendant difficulties, expansion should be made without the use of lubricant and preferably by means of a tapered mandrel. 6.2 Preparation for welding The tubes may be located by means of GTAW tack welds. These tacks shall form part of the procedure qualification. All such tacks shall be completely fused during subsequent tube end welding. By agreement between the Purchaser and Manufacturer, special punches may also be employed to secure tubes to the tube-plate, e.g. the punch may be designed to enable three equally spaced teeth to throw burrs from the tubeplate hole towards the tube. All burr depths must be sufficiently shallow to enable all such areas to be fully fused out during welding. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 15 Recommendations for tube end welding 16 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 7. Preheat and interpass temperature 7.1 General Even in tube-plates of considerable thickness, the effect of metal removal to form a large number of holes arrayed in close proximity, usually separated only by comparatively thin ligaments, results in a significant reduction in the mass quench effect. Due to the variation in geometric profile, ligament thickness and joint detail which influence the quench rate, it is impracticable to simulate actual production welding conditions in conventional tests devised to determine appropriate preheat temperatures. Although the effect of ligament thickness variation, proximity to flanges, etc., must be borne in mind, the following table of preheat temperatures, which are based on practical experience, may be used as a general guide. Maximum interpass temperatures are limited by the essential variables of ISO 15614-8, but shall not exceed the values shown in the table below without supporting documentation acceptable to the Purchaser. Table 1 Preheat and interpass temperatures Tube-plate Preheat Temperature Interpass Temperature Carbon (<= 0.26%) steel No preheat * 250° C. max Carbon (> 0.26%) steel 50° C. min 250° C. max 1% Cr ½% Mo 1¼% Cr ½% Mo 100° C. min 250° C. max 2¼% Cr 1% Mo 4/6% Cr ½% Mo 200° C. min 300° C. max Austenitic stainless steels None* 150° C. max 22% Cr duplex stainless steel None* 150° C. max 25% Cr super duplex stainless steel None* 100° C. max Titanium & Zirconium None* 150° C. max Other non ferrous alloys None* Material Dependent * No welding is permitted if the plate temperature is below 5° C. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 17 Recommendations for tube end welding 7.2 Practical limits The preheat and interpass temperature used in production shall be, within practical limits, the same as that used in the procedure test. Experience has shown that because of the increased restraint offered by the larger assembly, the preheat necessary in production may exceed the minimum necessary to obtain satisfactory welds in the procedure test. For this reason an allowance should be made for this effect in determining the preheat temperature chosen for the procedure test. Temperatures shall be measured preferably by contact thermocouple. If temperature indicating crayons are employed, care should be taken to avoid contaminating welding zones. 7.3 Weld interruption In the event of welding being interrupted on carbon and low alloy steels, the weld joint shall be insulated and allowed to cool slowly if the interpass temperature is not maintained. Before welding is resumed, the section to be welded shall be brought back to the required preheat temperature. When welding is completed, the joint shall be allowed to cool slowly. 7.4 Preferred means of preheating Electrical means of pre-heating shall be used wherever possible. Fixed gas burners may be used for preheating and maintaining the preheat, provided that an adequate degree of control can be demonstrated. 18 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 8. Welding 8.1 General 8.5 Additional controls The tubes shall be welded to the tube-plate using the approved procedure (see clause 3). When welding with the tube-plate in the vertical position, particular care should be taken to ensure a uniform weld profile. Any over-run or spillage of weld metal into the bores of the tubes which is considered detrimental shall be cleaned out and spatter removed. Certain materials require additional controls on welding parameters, equipment, or consumables to ensure satisfactory metallurgical or mechanical properties are achieved. Examples include, but are not limited to: 8.2 Welding individually All tubes shall be welded individually. Such procedures as ‘figure of 8’ welding and other complex welding patterns are not recommended. 8.3 Distortion minimisation The tube joints shall be welded in such a manner as to minimise distortion of the tube-plate. Unless otherwise agreed, where multi-run welds are used, no second run shall be deposited until the first run has been completed, cleaned as necessary and the weld visually examined. • Specific heat input controls for duplex stainless steels. Recommended limits are: • 1.5kJ/mm maximum for 22% Cr duplex stainless steels. • 1.0kJ/mm maximum for 25% Cr super duplex stainless steels. • Additional shielding gas application and purge hold times for titanium or zirconium alloys. • Material segregation to avoid contamination. Note that this may also affect handling and mechanical processes in addition to welding, such as material storage, lifting, and tools such as mandrels. • Low melting point materials and alloys should not be brought into contact with either tube-plate or tube ends. 8.4 Autogenous welding Autogenous welding is not permitted unless agreed with the Purchaser. When this is agreed, the Purchaser shall specify additional tests to be carried out during qualification to ensure suitable corrosion and mechanical properties are maintained. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 19 Recommendations for tube end welding 20 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 9. Post-weld heat treatment 9.1 General The post-weld heat treatment of complex assemblies such as welded tube end connections may present difficulties. Where acceptable, consideration should be given to methods of eliminating the need for post-weld heat treatment, eg. finite element analysis coupled with a fracture mechanics assessment. 9.2 Heating rates Where post-weld heat treatment is essential to reduce the hazard of stress corrosion cracking associated, for example, with nitrate or caustic service, it is important that the rate of heating and cooling during heat treatment is controlled to avoid the possibility of weld fractures and excessive tube distortion. The heat balance between the tubes and shell must be controlled so as to avoid excessive temperature differences. Where practicable, the assembly should be charged into a cool furnace, the temperature raised slowly and uniformly to the required post-weld heat treatment temperature and then allowed to cool to ambient temperature within the furnace. Provision for adequate tube support to limit distortion must be considered at the design stage. The precise procedure and temperature shall be agreed beforehand between Purchaser and Manufacturer. 9.3 Additional welding If for any reason, any tube end welding, however slight, is carried out after heat treatment, it is recommended that the post-weld heat treatment should be repeated, when such post-weld heat treatment has been specified as a requirement. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 21 Recommendations for tube end welding 22 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 10. Quality control and health and safety 10.1 General The Manufacturer shall operate a quality management system that conforms to ISO 9001 and ISO 3834. Comprehensive quality requirements shall apply in accordance with ISO 3834-2. The Manufacturer welding engineer shall be appointed as the principal EN ISO 14731:2006 welding coordinator and shall provide technical oversight of the fabrication techniques, production welding and NDT. All production welding shall be supervised by this welding coordinator or a competent welding supervisor experienced in the application of the process being applied, particularly at the commencement of each shift or change of operator. For all processes, all meter readings and machine settings shall be checked prior to the start of each shift to ensure that they are in accordance with those established during procedure qualification. Any change of a significant variable, but not a replenishment of any consumable such as a replacement gas cylinder or welding consumable, shall require re-qualification of procedure (see clause 3.1). 10.2 Samples At the commencement of each shift, a minimum of one sample shall be welded using a tube from production material and plate of the same nominal composition as that used in the fabrication. This sample shall be sectioned and shown to be at least equal in quality to that required for procedure qualification. If the sample is found to be unsatisfactory, the cause shall be established and the test repeated prior to production welding. At the risk of the Manufacturer, production need not be delayed until the test weld is approved, but if the sample is unsatisfactory, those welds affected shall be rectified as required to the satisfaction of the Purchaser and inspection body. 10.3 Examination of materials 10.3.1 Tubes All tubes shall be subject to visual examination before fitting. For some special duties it may be necessary, prior to assembly, to inspect the ends of the tubes for defects, by non-destructive testing; where this is specified, techniques and acceptance levels shall be subject to agreement between Purchaser and Manufacturer. 10.3.2 Tube-plates All tube-plates shall be examined visually for surface defects. It is recommended that the tube-plate should be examined ultrasonically; acceptance levels shall be subject to agreement between Purchaser and Manufacturer. 10.4 Health and Safety The Manufacturer shall operate a comprehensive Safe System of Work, including risk assessments for all activities. Unless local regulations are more stringent, the following shall apply: • Protective clothing for use in welding and allied processes shall conform to ISO 11611; • Equipment for oxygen and acetylene shall conform to ISO 14114 and ISO 5172; • Welding equipment shall conform to IEC 60974-x; • Ventilation of welding and cutting fumes shall conform to ANSI Z49.1 / AWS Z49.1. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 23 Recommendations for tube end welding 24 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 11. Cleaning and inspection 11.1 General After welding the tube-plate face, the welds and the internal tube surface to a distance of at least 3mm beyond the fusion line must be cleaned thoroughly by wire brushing and examined carefully for surface defects. Defects such as cracks, gross porosity, slag inclusions and lack of fusion shall be remedied. 11.2 Dye penetrant testing Where a more searching examination is required, the tube-plate surface may be subjected to dye penetrant testing in accordance with an approved procedure. Repairs shall be made to any areas of the welds showing potential leaks such as pores or cracks, as evidenced by signs of red dye. 11.3 Other Other examination techniques may be applied subject to the Purchaser’s agreement. For critical applications, as defined by the Purchaser, microradiography shall be applied. In all cases, NDT procedures shall be prepared by an ISO 9712 level 3 qualified NDT supervisor. The NDT procedures and acceptance criteria shall be subject to Purchaser approval. Technicians carrying out NDT must be qualified to ISO 9712 level 1, with sentencing performed by technicians qualified to level 2 or level 3. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 25 Recommendations for tube end welding 26 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 12. Leak detection 12.1 General 12.3 Gas leak testing Since the repairs of leaks detected by hydrostatic testing may be complicated during re-welding by the boiling of entrapped water behind the weld so causing weld porosity, the hydrostatic test shall be preceded by a low pressure air test or, preferably, by a gas leak test (see clauses 12.2, 12.3 and 12.4). Where greater sensitivity to leaks is required, a tracer gas leak test is preferred to an air test. The use of helium, hydrogen or argon as the tracer gas is permissible, but for reasons of economy, argon is preferred. The sniffer gun or detector, which is sensitive to any gas having a thermal conductivity different from that of air, usually has several ranges of sensitivity and the sensitivity is generally progressively reduced so as to pin-point precise leak sites. For both types of test, the tube bundle shall be placed in the shell and welded or bolted as designed and all openings blanked off. No liquid shall be applied to the shell side of the tube-plate prior to any gas leak test. Where manual multi-run welds are used there is an obvious advantage, particularly for heat exchangers for critical duties, in carrying out a leak test on the completion of the first runs only of all tube to tube-plate welds on both tube-plates. 12.4 Other leak testing Other methods of leak testing may be agreed between Purchaser and Manufacturer. Whatever method is agreed due consideration shall be given to environmental and health and safety issues. 12.5 Leak investigation 12.2 Air testing The assembly shall be tested for leaks by applying a pressure of 0.5bar. High pressure tests are not generally favoured due to the hazards of stored energy especially when volumes are large. While the shell is under pressure a simple soap or detergent test shall indicate escapes of air from leaks. Generally, a 2% solution by volume of an appropriate foaming agent in water is effective. Testing is also permissible employing air/nitrogen gas mixtures. All suspect weld locations shall be marked for repair. Defective welds found during leak testing shall not exceed 5% of the total number of welds on any tube-plate. Where a figure of more than 5% defective welds is revealed during test, a full investigation into the cause of this high incidence shall be conducted and the whole of the tubeplate and all tubes should, at the discretion of the Purchaser, be re-prepared and re-welded. For critical duties, this figure may be reduced by agreement. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 27 Recommendations for tube end welding 28 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 13. Repairs 13.1 Leaks On completion of a gas leak test, any leaks discovered shall be repaired and retested until all faults are remedied. The maximum number of repairs permitted shall be agreed between the Purchaser and Manufacturer. 13.2 Qualified procedure In general, faulty welds shall be completely removed to sound metal and repaired using a qualified procedure. Departure from this procedure shall be as agreed by the Purchaser and inspection body and may be subject to repair procedure testing. 13.3 Cause of defect When any defects occur, the cause shall be established prior to repair. If the defect is attributed to welder or welding operator error, then consideration shall be given to retraining and requalification. Conversely, repeated similar welding defects may indicate that the welding procedure should be modified and requalified. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 29 Recommendations for tube end welding 30 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 14. Tube expansion 14.1 General 14.4 Tube wall thinning Since tube expansion does not significantly contribute to the mechanical properties of properly applied strength welds and may even be harmful, this procedure is generally unnecessary and not recommended; however for certain service duties, e.g. where possible crevice corrosion or vibration fretting susceptibilities must be minimised, it may be necessary to provide for intimate contact between the OD of the tubes and the bores of the tube-plate holes. This may be accomplished by light expansion after both welding and successful leak testing (see clause 12) but before pressure testing (see clause 15). However where no crevice corrosion at all is permissible, the recommended joint detail is as shown in clause 2.4.7. The amount of tube wall thinning required depends on the materials and shall be agreed between the Purchaser and the Manufacturer. The percentage of the original tube wall thickness and the machine settings to achieve this thinning shall be determined and checked during procedure testing by micrometer measurements as follows: Diameter of tube hole: IDh Mean outside diameter of tube: OD Difference (total clearance): IDh -OD Inside diameter of tube after expansion: ID2 14.2 Location Inside diameter of tube before expansion: ID1 Tube expansion after welding shall lie within the zone from approximately 10mm from the weld junction to 3mm from the back of the tube-plate. Difference (Internal expansion of tube): ID2-ID1 Initial thickness of tube: t Tube wall thinning: ((ID2-ID1)-(IDh-OD)) * 100% 2t 14.3 Equipment Unless otherwise agreed with the Purchaser, the equipment used for tube expansion shall be of the mandrel and parallel roller type incorporating limiting controls to give a predetermined amount of tube wall thinning, e.g. controlled torque equipment. Special care should be taken to ensure that tube expansion equipment is clean and free of any contamination prior to use. If the equipment is used on more than one material type, Manufacturer shall provide a procedure for Purchaser approval detailing how crosscontamination is avoided. 14.5 Bores If the tubes are to be expanded after welding, the bores shall be inspected for evidence of distortion and/or weld spillage. It is permissible to lightly dress the bores to avoid jamming of the rollers during subsequent expansion, but care must be exercised to ensure the minimum removal of metal from the bores of the tubes. By agreement with the Purchaser, special techniques such as the insertion of tapered ceramic plugs in the bores, may be applied during welding to prevent weld spillage. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 31 Recommendations for tube end welding 32 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 15. Pressure testing 15.1 Cleaning 15.3 Leaks The tube-plate face, the welds and the internal surfaces of the tubes to a length of about 13mm shall be thoroughly cleaned by a suitable method; any grease present shall be removed either by the use of a solvent or by steam jets. After maintaining the specified pressure for a minimum period of 4 hours, the welds and bores of the tubes must be examined for leaks. The location of all leaks shall be marked on the tube-plate and recorded on a tube-plate drawing. 15.2 Final acceptance pressure test 15.4 Repair The final acceptance pressure test shall be conducted at 1.5 times the maximum design pressure minimum, or higher if required by the application standard or Purchaser. All leaks shall be repaired by welding as agreed by the Purchaser. Such repairs shall be subject to further pressure testing. Clean kerosene may be used and is more searching when hydrophobic residues such as oil or grease are present, but attention is drawn to the risk of fire. If water is used, it is recommended that 2% by volume of an approved wetting agent or detergent should be added. The surface tension of a 2% detergent solution is about 30mN/m compared with plain water at 75mN/m and kerosene at 25mN/m. The possible risk of corrosion by the use of detergent is minimised by the careful selection of additions and control of the amount used. Detergents are also available which carbonise at low temperature of the order of 150° C. The addition of 0.2% sodium nitrite to the water is recommended as a corrosion inhibitor; if austenitic materials are used the chloride content of the water should not exceed 30ppm. Where this is impracticable the equipment shall be flushed out with water containing not more than 10ppm chloride for services where trans-granular stress corrosion could occur. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 33 Recommendations for tube end welding 34 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 16. Draining and dewatering 16.1 General The vessel shall be drained thoroughly after testing and where specified a suitable dewatering fluid may be used. 16.2 Heating If the heat exchanger is required to be completely dry, e.g. for SO2 duties, the assembly should be heated by an appropriate method to a temperature that is sufficiently high to remove all water, particularly from the interstices between the tubes and the tube-plate. If the bundles are of stainless steel, the heat exchanger should be washed out with water containing not more than 10ppm chloride before heating. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 35 Recommendations for tube end welding 36 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 17. Supervision and inspection 17.1 General There shall be systematic supervision and control of all stages of the work by competent persons (see clauses 10 & 11) having adequate experience and knowledge of the welding process being employed. Records of test plates and production welds shall be kept and made available to the Purchaser. 11. When the heat exchanger or tube bundle has been drained, dewatered or dried out as specified and is ready for delivery (clause 16). 17.2 Inspection and Test Plan (ITP) As a minimum, each of the following hold/witness points should be included in the Purchaserapproved Inspection and Test Plan (ITP): 1. When procedure qualification test pieces are prepared ready for welding (clause 3). 2. When operator qualification test pieces are prepared ready for welding (clause 4). 3. When procedure and operator qualification test pieces are sectioned for examination (clause 3.2). 4. When the production tube-plate holes are drilled, and prepared as required, and are ready for assembly (clause 5). 5. When the tubes are fitted and tube ends and tube-plate are cleaned immediately prior to the commencement of welding (clause 8). 6. Visual inspection on the completion of all welding (clause 11). 7. During leak detection with gaseous penetrant and subsequent repairs, if required, and re-detection (clauses 12 and 13). 8. During gas leak detection after tube expansion, if required (clause 14). 9. During gas leak detection after heat treatment, where called for (clause 9). 10. When pressure testing and acceptance is carried out (clause 15). EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 37 Recommendations for tube end welding 38 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 18. Records In addition to the requirements of ISO 3834-5, the Manufacturer shall hold and regularly maintain adequate records of all qualification tests and production experience, including parameter monitoring/test results and weld reject rate, for each welder. EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association 39 Recommendations for tube end welding 40 EEMUA Copyright © 2017 The Engineering Equipment and Materials Users Association Publication 143 Recommendations for tube end welding Publication 143 References Specifications and Standards 1. ANSI Z49.1 (2012) / AWS Z49.1 (2012) Safety in Welding, Cutting and Allied Processes 2. ASTM E562 (2011) Standard Test Method for Determining Volume Fraction by Systematic Manual Point Count 3. ASTM G48 (2011/R 2015) Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution 4. EN ISO 14731:2006 Welding coordination Tasks and responsibilities 5. IEC 60974-x IEC standards for “Arc welding equipment” - Parts 1-13 6. ISO 11611 (2015) Protective clothing for use in welding and allied processes - Second Edition 7. ISO 14114 (2014) Gas Welding Equipment - Acetylene Manifold Systems for Welding, Cutting and Allied Processes - General Requirements - Second Edition 8. ISO 15614-1:(2004) 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 (+ later amendments 1 & 2) 9. ISO 15614-8:2016 Specification and qualification of welding procedures for metallic materials — Welding procedure test —Part 8: Welding of tubes to tube-plate joints 10. ISO 3834-1 (2005) Quality requirements for fusion welding - of metallic materials - Part 1: Criteria for the selection of the appropriate level of quality requirements - Second edition 11. ISO 3834-2 (2005) Quality requirements for fusion welding of metallic materials - Part 2: Comprehensive quality requirements - Second edition 12. ISO 3834-5 (2015) Quality requirements for fusion welding of metallic materials - Part 5: Documents with which it is necessary to conform to claim conformity to the quality requirements of ISO 3834-2, ISO 3834-3 or ISO 3834-4 - Second Edition 13. ISO 5172 (2006) Gas welding equipment Blowpipes for gas welding, heating and cutting Specifications and tests - Third Edition (including amendments 1 & 2, 2015) Other References 14. TEMA Standards of Tubular Exchanger Manufacturers Association. 5th Edition, 1968. 15. IIS/IIW recommendations International Institute of Welding “Recommended Welded Connections for Pressure Vessels”. I.I.S./I.I.W. -237-66. 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