Welding Journal ~ Need For Weld Purity Drives Purging Methods
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The article discusses the need for high purity welds in industries like pharmaceuticals, semiconductors, and food production due to stringent purity requirements. This has driven the development of specialized purging methods and equipment to prevent oxidation during welding and contamination of the weld. Advances include expanding plugs and inflatable seals to provide gas seals during welding, as well as integrated purge systems that allow for heating and non-destructive testing with the system in place. Monitoring instruments have also been developed to measure low oxygen levels in purge gases. The ASME B31.3 process piping code revisions have further stimulated innovations in purge systems to meet purity standards for applications in these industries.
Welding Journal ~ Need For Weld Purity Drives Purging Methods
- 1. PUBLISHED BY THE AMERICAN WELDING SOCIETY TO ADVANCE THE SCIENCE, TECHNOLOGY, AND APPLICATION OF WELDING AND ALLIED JOINING AND CUTTING PROCESSES WORLDWIDE, INCLUDING BRAZING, SOLDERING, AND THERMAL SPRAYING July 2012 WELDINGJOURNALVOLUME91NUMBER7JULY2012 July 2012 Cover_4/06 Cover 6/7/12 5:42 PM Page C1
- 2. 3WELDING JOURNAL CONTENTS 30 Finishing Stainless Steel Welds for Food Processing Equipment Choosing the right finishing abrasives ensures smooth and corrosion-free welds on food processing equipment D. Long 36 Need for Weld Purity Drives Purging Methods The need for high-purity welds in pharmaceuticals, semicon- ductors, and food production requires purging considerations M. J. Fletcher Welding Journal (ISSN 0043-2296) is published monthly by the American Welding Society for $120.00 per year in the United States and posses- sions, $160 per year in foreign countries: $7.50 per single issue for domestic AWS members and $10.00 per single issue for nonmembers and $14.00 single issue for international. American Welding Society is located at 550 NW LeJeune Rd., Miami, FL 33126-5671; telephone (305) 443-9353. Periodicals postage paid in Miami, Fla., and addi- tional mailing offices. POSTMASTER: Send address changes to Welding Journal, 550 NW LeJeune Rd., Miami, FL 33126-5671. Canada Post: Publications Mail Agreement #40612608 Canada Returns to be sent to Bleuchip International, P.O. Box 25542, London, ON N6C 6B2 Readers of Welding Journal may make copies of articles for personal, archival, educational or research purposes, and which are not for sale or resale. Permission is granted to quote from arti- cles, provided customary acknowledgment of authors and sources is made. Starred (*) items excluded from copyright. Departments Editorial ............................4 Press Time News..................6 News of the Industry ..............8 International Update ............14 Stainless Q&A ....................16 RWMA Q&A ......................18 Letters to the Editor ............22 Product & Print Spotlight ......24 Brazing & Soldering Today Technology News ..............63 Brazing Profiles ................70 Conferences ......................74 Coming Events....................76 Certification Schedule ..........80 Society News ....................81 Tech Topics......................84 Interpretations D1.6M:2007 ..84 Guide to AWS Services ......101 Welding Workbook ............102 Personnel........................104 Classifieds ......................106 Advertiser Index ................109 187-s Scaling Thermocapillary Weld Pool Shape and Transport Variables in Metals Molten pool shape and thermocapillary convection were predicted from scale analysis P. S. Wei and H. J. Liu 195-s Characterization of Three-Dimensional Weld Pool Surface in GTAW An innovative vision system was tested to give backside bead width for determining weld penetration W. Zhang et al. 204-s Identifying Performance Differences in Transmissive and Reflective Laser Optics Using Beam Diagnostic Tools The changes in properties of laser beams delivered using transmissive and reflective optic systems were characterized J. Blecher et al. Features Welding Research Supplement 30 42 36 July 2012 Volume 91 Number 7 AWS Web site www.aws.org On the cover, from top: brazed automotive steel parts (Carmen Paponetti), and titanium-to-chromium brazements; brazed carbon steel parts (Carmen Pa- ponetti); a brazed Portuguese filigree ship model (Michael Y. Reyzer), and torch brazing of a copper heat exchanger (Prof. I. N. Pashkov); and the Vortex Rapid Finish disc (Norton Abrasives), and vacuum brazed stainless steel to titanium tubes (Justin Liguori). (Brazing photos courtesy of Alexander E. Shapiro.) Brazing & Soldering Today 38 IBSC 2012 Attracts Worldwide Audience The 5th International Brazing and Soldering Conference drew attendees, applications, technologies, and science from around the world K. Campbell 42 Defect Assessment of Brazed Steel Components The influence of flaws on the properties and fatigue behavior of brazed components was evaluated C. Leinenbach et al. 50 A Composite Solder Alloy Preform for High-Temperature Lead-Free Soldering Applications A laminated preform applied with pressure provided sound solder joints W. Liu et al. 60 Managing Precious Metal Volatility in Brazing Alloys The rising costs of precious metals have put pressure on the brazing and soldering industries to more closely manage their product production and application G. Alexy July 2012_Layout 1 6/7/12 5:20 PM Page 3
- 3. JULY 201236 Demands for improvements in piping fabrication quality have risen exponen- tially in recent years. The latest version of the ASME 31.3 Process Piping code (Ref. 1) is a formal recognition of this emerging requirement that has been stimulated mainly by the bioprocessing sector, but also by associated industries such as pharmaceuticals, semiconduc- tors, and food production. An essential element in pipework is the production of welded joints. The stringent inspection procedures imposed by ASME 31.3 apply as much to welded joints as they do to all the other fabrica- tion processes involved. The article noted in Ref. 2 highlighted more general aspects of the significance of the latest edition of the code as it ap- plies to the manufacture of high-quality pipework. Producers of welding acces- sories designed specifically to meet the requirements have been quick to meet the new challenges ASME B31.3 impose. The Problem One of the fundamental requirements imposed during the welding of pipes is to prevent oxidation of the weld during the first pass. The welding torch provides inert gas coverage of the top of the fu- sion zone, but unless precautions are made there is no coverage of the weld root. The problem has always been rec- ognized and over the years a variety of solutions have evolved, some eccentric, others practical but largely ineffective. While minimum standards are set for all fusion welding, the application to the pharmaceutical, semiconductor, and food production sectors demands partic- ularly high standards of cleanliness. Hy- gienic purity is the driving force for joints destined for use in pharmaceutical and food production. Elimination of particu- late contamination is the crucial require- ment in semiconductor manufacture. With some semiconductor manufac- turers producing chips with dimensions at the 32-nanometer (nm) level, and re- search going on at the 15-nm level, it is easy to see why the design, fabrication, and maintenance practices required to ensure exacting purity requirements of their process fluid distribution systems are of paramount importance. In the food processing industries, statutory legislation and a plethora of lit- igation suits have forced plant manufac- turers to introduce quality control levels previously considered unnecessary. Con- tamination introduced during fabrication is now unacceptable. Need for Weld Purity Drives Purging Methods MICHAEL J. FLETCHER (barrow@post.com) is chief executive officer, Delta Consultants, Rutland, UK. BY MICHAEL J. FLETCHERDesign, fabrication, and maintenance practices that can meet exacting purity requirements of ASME 31.3 are crucial to the food, pharmaceutical, and semiconductor industries Fig. 1 Schematic section through tube joint illustrating gas seals on each side of the weld. The identifiers show access routes for inert gas supply/exhaust. Fig. 2 Nylon/rubber expanding plug in common use for tube sealing. Fig. 3 Inflatable neoprene pipe seal. Fletcher Feature July 2012_Layout 1 6/6/12 8:07 AM Page 36
- 4. The Solution Satisfying the high level of protection lies in selection of specialized purging equipment. Inserting low-quality paper or other barrier material on either side of the joint and filling the space between them with inert gas may be good enough for low-level requirements but is unsuit- able to meet the requirements ASME B31.3 imposes. Significant progress was made in purging equipment in the 1980s when welding accessory manufacturers devel- oped expanding plugs and inflatable stoppers (Figs. 13). These devices gave assurance of effective sealing with the pipe wall and prevented leakage of inert gas from the weld zone, thus precluding backflow of oxidizing gases from the at- mosphere. Generally effective, these develop- ments still allowed considerable scope for innovative improvements. Devices such as shown in Fig. 4 integrate a pair of inflatable bladders and provides pres- sure-controlled gas ports for both inflat- ing and inert gas supplies. Other systems have been designed to satisfy the requirements of pre- and post- weld heating through the use of thermally resistant materials Fig. 5. Some are produced with no metallic materials in the weld vicinity so that postweld nonde- structive examination can be undertaken with the purge system still in place. There have been significant develop- ments recently in gas-monitoring instru- ments. These incude devices such as monitors (Fig. 6) designed specifically for measurement of low oxygen levels in purge gases during welding. The challenges of the ASME Process Piping code have provided a stimulus for further developments, and advanced ver- sions of commercial purge systems are becoming available. Some of these em- ploy high-stability engineering polymers to cover all exposed metal components so that the risk of transfer of metallic ma- terials onto pipe surfaces is minimized. Many are able to provide fully automatic control over inert gas flow and pressure. The welding supply industry is re- sponding proactively to the demands imposed by the latest edition of ASME 31.3. References 1. ASME B31.3, Process Piping, Chap- ter X, High Purity Piping. 2010. New York, N.Y.: American Society of Me- chanical Engineers. 2. Huitt, W. M., Henon, B. K., and Molina III, V. B. 2011. New piping code for high-purity processes. Chemical En- gineering, July. 37WELDING JOURNAL Fig. 4 This purge system was designed specifically for rapid deployment and in足 corporates gas entry and exit routes. Fig. 5 Thermally tolerant, fully inte足 grated purge systems developed for use where pre足 and postweld heating is re足 quired Fig. 6 Sensitive monitoring instrument for measuring oxygen content in purge gas. 4 6 5 Learn how you can more easily obtain and maintain mandated food grade 鍖nishes. Call 800-342-9015 Wide Selection of Contaminant Free Tools for Cutting, Grinding and Finishing Stainless Steel Specializing in Metal Finishing Solutions For Food Processing Industry For info go to www.aws.org/ad-index Fletcher Feature July 2012_Layout 1 6/6/12 8:08 AM Page 37