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PWL #031-EGW, UI for all, Filler Metal Resources, Safety, PAW Tips, Thermite Welding March 01, 2006 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. Electro Gas Welding, Ultrasonic Inspection for all, Filler Metal Resources, Safety, Plasma Arc Welding Tips, Thermite Welding and more...
This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers.
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Date: March 2006 - Practical Welding Letter - Issue No. 31
1 - Introduction 2 - Article: Electrogas Welding 3 - How to do it well: Ultrasonic Inspection for all 4 - Filler Metal Resources 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: Safety Practices 8 - Site Updating: Plasma Welding Tips 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Thermite Welding 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction
Welcome to our 31st issue of Practical Welding Letter. By combining the two, developers succeeded in providing a window of opportunities within which this Electrogas Welding process competes economically with older solutions. Then we present the case for application specific semi automatic ultrasonic testing whose main advantage is disposing of a certified inspector. It can be preferable to the alternative when the job is repetitive and highly standardized. A few online Filler Metal Resources introduced here can provide documented answers to hard questions. Although compiled by commercial suppliers, the data are believed to be reliable for background information and can be supplemented by further inquiry. Safety practices should be probably studied, learned and applied with more attention than is now devoted to the subject. The personal health and well being of welders is at stake. We present a short reminder of important points with links to articles stressing selected items in different ways. For our Website Update we report on our very last addition, on Plasma Welding Tips. At the same time we invite our readers to subscribe at no cost to an additional updating service of ours. We think it should be welcome and useful. In the Contribution department we report on an old process and on the improvements that could be achieved by applying modern investigation and development techniques. Other columns are found in their usual place. We call for your input. Write us by e-mail. Click here to send us Your Questions and Feedback. 2 - Article: Electrogas Welding Our readers may recall that in the last issue of Practical Welding Letter, PWL#030, we published a note on "Process Extensions of GMAW". We left out one more extension, the object of this article, probably deserving more than a short note. A full presentation is given here of quite a specific process that is fit for a class of applications where it is performing successfully and economically. We should recognize that the number of different welding processes is quite large. It means that people working in welding are ready to try and explore new ways to do things better, faster, cheaper, by twisting and modifying older ideas and by combining different means from other known solutions. One of these sideways explorations brought up the development of a new mechanized process called Electrogas Welding (EGW). It is essentially an extension of the well known and proven Electroslag Welding (ESW) process, capable of welding thick plates with a single pass vertical application. An article on ESW was published in the issue 7 of Practical Welding Letter for March 2004 visible by clicking on PWL#007. The new process was adapted to weld thinner plates in the range of 13 to 38 mm (0.5 to 1.5 in), but later on extended to other values as well. It combines a set-up similar to that used for ESW with equipment used for Gas Metal Arc Welding (GMAW) and/or for Flux Cored Arc Welding (FCAW). The heat source is an electric arc struck between a continuously fed filler metal electrode and the weld pool. There is a need of a starting weld tab, to seal the bottom of the open joint, permitting the build up of a molten metal weld pool. Use is made of fixed or movable water cooled copper backing shoes to dam or confine the molten metal pool from both sides of the joint. Sometimes one fixed shoe is placed from one side, and a movable one on the other side. While the direction of progression is vertical up, the weld metal is deposited in the flat position. Power sources, preferably of the constant voltage type, rarely of constant current type, usually supply direct current reverse polarity, electrode positive (DCEP) . Capacity could be up to 1000A. Duty cycle of 100% must be assured without interruption for work going on for many hours. The EGW process is used for carbon steel, structural steels and pressure vessels steels. It is not used for aluminum or stainless steels. Filler metal is provided by a solid or flux cored electrode continuously supplied within a consumable or nonconsumable electrode guide. The AWS classification separates solid wires (S) from flux cored (T = Tubular) in the following Filler Metal Specification: ANSI/AWS A5.26/A5.26M-97(R2003) Shielding comes either from flux decomposition, from protective gas or from both. Square butt joints are used with spacing between plates of about 22 m (7/8 in). To decrease the volume of filler metal needed, beveled edges can be used. The most important advantages of electrogas welding are high deposition rates, simple joint preparation and cost savings achievable for vertical welding with a continuous process. Among the limitations are high cost of equipment, relatively long setup time, critical training of operators and the need to complete the weld in one pass. If a restart is needed it may be problematic. Quality is inspected by classical inspection methods. A well conducted process has a high potential for excellent quality. Approved welding procedures should be used. Otherwise quality could be compromised by internal porosity, weld cracking or external defects. Low toughness values may be sometime exhibited by coarsened grains developing in this slowly cooling process. Preheat and post weld heat treatments are not normally needed. In conclusion the electrogas welding process has the potential to produce high quality welded joints with considerable economic advantage when compared with alternative processes, if its unique characteristics can be exploited.
3 - How to do it well: Ultrasonic Inspection for all Ultrasonic Testing is a mature and robust non destructive inspection technology capable of detecting small and dangerous flaws within material bodies. As such it is widely used within the welding industry for providing safe and secure proofs of acceptable process performance meeting exacting requirements. It is based on the properties of propagation of sound waves, of such a high frequency as to be inaudible by the human ear, and on their capacity to be reflected by geometric features or by internal imperfections. When combined with radiographic inspection both technologies supplement each other due to their somewhat different sensitivity to specific geometric details of lack of soundness. For all of its practical success, ultrasonic inspection has one major drawback. It is labor intensive. Moreover ultrasonic inspectors require a long formal education and preparatory apprenticeship consisting in theoretical studies covering specific chapters of acoustics, a branch of physics, and a long practical training under the supervision of experienced instructors. Finally the trained personnel must take complex examinations and obtain a Certification demonstrating their capacity to perform successful ultrasonic inspections in order to be cleared for employment by industrial contractors, according to requirements of binding Specifications or Codes. Various attempts are being done to automate as much as possible the ultrasonic inspection of welds in specific joint configurations. Such efforts are reported in an article published in the Issue 23 of Practical Welding Letter for July 2005. It can be read by clicking on PWL#023. When the inspected items are repetitive and the requirements, relative to acceptance conditions, are clearly cut, some manufacturers find that it is more attractive to use equipment set up only for the specific configurations needed. In particular this attitude is successfully applied for inspecting mechanized or robotic welds as they are performed, in line, by a welder or a helper with no specific ultrasonic training. The body to be inspected is set-up by placing it in a well defined position relative to the sensor (called transducer), and starting the test. A mechanical scanning movement may be used if necessary. The automatic answer or inspection result is either to accept or to reject. This is made possible by electronic manipulation of the visual signal, on a screen, representing the behavior of the ultrasonic beam. Apart from the entrance and back peaks signaling echoes from known geometric features of the body inspected, any further peak is suspected of being caused by reflections from unwanted discontinuities. Its intensity is measured as height from the baseline (on the screen) and its position or depth in the body is inferred from the linear relationship between the position of the reflector in the body and the horizontal distance of its signal trace from the entrance peak. A "gate" that limits the inspected volume to the location of interest for the inspected body is superposed on the signal. Any signal appearing in the volume of interest (that is within the gate) and of intensity higher than that of an established threshold for that specific inspection will trigger rejection. The threshold is established by reference to ultrasonic reflections from known discontinuities of definite dimensions, introduced on purpose in special reference test pieces. Failed items can be then subjected to additional inspection by certified ultrasonic inspectors for further decision if needed. Specific applications of the above principles were successfully employed also for routine examinations of critical aircraft details, where the integrity of certain components must be assured by periodic inspection. The possible economic advantage of such a solution relative to a general ultrasonic testing performed by a certified inspector, has to be examined case by case by comparing the costs of equipment and operation.
4 - Filler Metal Resources A nice little book called It contains an introduction to Welding Metallurgy, reference information on welding in general and then detailed standard and composition data on many types of filler metals. Comparison of international standards and useful tables and references are presented. The Table of Contents and the alphabetical index help in finding the subjects of interest. We recommend to all our readers to download and save this book in a working folder for easy offline access. Another Resource from a Commercial Supplier provides a lot of insight. See it at It has a lot of information to explore, using the buttons of the NavBar or performing searches. Interested readers should take their time to explore the resource and see which specific knowledge is useful to them. For information obtainable from the catalog of the same Company see: Other welding consumable suppliers display articles and catalogues online that should be explored if specific answers are sought. See:
5 - Online Press: recent Welding related Articles From AWS From The Fabricator From TWI From ESAB (a commercial supplier)
6 - Terms and Definitions Reminder Active Flux used for Submerged Arc Welding is specially formulated to influence the composition of the resulting welds depending on selected parameters mainly voltage. Arc time or arc-on time in an arc welding operation is the duration of time when the arc is maintained. It is used to calculate the ratio of arc time to total time, and the duty cycle. Balling up is the formation of globules of material in case of inadequate wetting. In GTAW, it indicates also the formation of a ball at the tip of tungsten electrode as the preferred shape for AC welding. Clad metal is a layer of metal different from the base, applied by one of a series of processes, to impart specific surface properties not readily presented by the bare base metal itself. Downslope time is preset to allow for the linear decrease of current between two predetermined current levels, usually at the end of a weld cycle in certain automated processes. Expulsion is a faulty condition whereby molten metal is ejected from the nugget of a resistance weld, generally due to inadequate parameters. Melting range of a metal or alloy is the temperature interval between liquidus and solidus. Upslope time is preset to allow for the linear increase of current between two predetermined current levels, usually at the beginning of a weld cycle in certain automated processes.
7 - Article: Safety We reviewed already, in our Website page on Safety, some essential aspects of protecting Welders in the Welding Workplace. In this short note we wish only to bring to the readers' attention some of the most important issues that must be taken care of. The subject of Safety in Welding does not enjoy, unfortunately, first priority among those working in the branch. It is a pity, considering the dangers. It is possibly so because it is less interesting than other technical issues, or because it is perceived as introducing limitations and hindrances in the speedy performance of jobs, or because it is considered tiresome. Nevertheless, even if some workers may tend to neglect safety provisions designed to protect them from cumulative or sudden damages, it is a clear responsibility of management to enforce all measures of safety in the workplace. In all technologically advanced countries there is a central authority, like the Ministry of Labor, in charge of issuing and enforcing laws and directives. Specific requirements refer to all activities involving welding and associate preparatory or finishing work. Management is bound to issue a policy document declaring its commitment to the constant application of safe practices. Within this general framework, executives use to give to a responsible and professional employee the task and the authority of assuring that safety practices are in fact applied. Effective Training sessions must be given periodically to all workers, and clear and visible plates with warning of dangers and instructions, among others, on the obligation to wear eye protection, must be exposed near the work area. See: Good Housekeeping requires that the workplace be at all time clean and free from obstructions risking to be overlooked by welders wearing helmets or masks and by other workers temporarily dazzled by intensive light. Escape routes shall be clearly marked and clear at all times from obstacles and materials to allow for safe and orderly evacuation in case of a sudden danger. Employers must provide Personal Protective Equipment of the correct types and quality to affected workers. General procedures including training must be established and effective usage must be supervised. See: Welders' eyes, face, head must be protected from the dangers of heat, light, flying particles or molten metal drops and other irritant or dangerous materials. See: Hands, feet and body must be protected from burns, bruises, abrasions, cuts and dangerous chemical exposure. Hearing protection must be provided to all exposed to excess noise. Welding and related processes can release noxious fumes and gases that may have adverse effects on the health of those exposed to them. Therefore adequate ventilation is important particularly in confined spaces. Aspiration hoods should be used and powered personal respirators may be needed. See: Compressed Gases need particular attention according to special instructions from manufacturers and from Trade Associations. Cylinders need periodic inspection and testing to be approved for continuing use. See publications from CGA - Compressed Gases Association at www.cganet.com/ Electrical Safety starts with thorough training on the dangers of electric shock and depends on constant and professional maintenance being performed on cables and contacts. Welders should be trained to recognize dangerous conditions and instructed to call for prompt Maintenance and Repair. Fire prevention consists in making sure that combustible materials are not present in the surroundings of places where welding or cutting are performed.
Nonetheless specially trained fire watchers should be in charge of assuring that no dangerous activities are performed which could generate a fire. Fire extinguishers and suitable fire fighting equipment should be readily available.
See: Explosion can follow if explosive gases or vapors are mixed with air in explosive proportions. Training, precise instructions and equipment in perfect condition following periodic checks will avoid dangerous leaks. Machinery must be surrounded by protective guards to prevent injuries. Special welding Machinery needs safeguarding of switches and foot pedals to avoid unintended sudden movements of parts that may endanger workers or bystanders. High Energy Welding equipment present special hazards, usually taken care of by manufacturers. Secondary X-Radiation in Electron Beam Welders is normally shielded by the vacuum chamber. Laser Beams can inflict eye injury. Operators need comply with requirements and instructions supplied by manufacturers. Robotic Operation is better performed within enclosed cells where access to workers is permitted only when machinery movements are disabled. Different safeguarding devices are implemented but training is the most important part of any program aimed to implement safety procedures. Many important publications on Health and on Safety for the welding industry are available from the American Welding Society. Download the 2006 Catalog of AWS publications from Managers in charge of welding operations should procure and study the safety documents issued by authorities and professional societies. See also It is recommended to download at no cost and to study the Standard
8 - Site Updating: Plasma Welding Tips Continuing our series of "Tips" we propose in the Page of this Month to remind some basic facts and information on Plasma Arc Welding. To read the page click on Plasma Welding Tips (Opens a new Page). Given the vast variety of processes available, it may become quite difficult to select, for any specific job, the one having the potential to perform quality work at the minimum cost. It is therefore important that Welding Decision-Makers have a large knowledge and experience base. Furthermore they should be able to use practical help to reach informed sources of general orientation to find their way. We would like to be able to say that, to the readers looking for our advice, we are in fact providing useful information. As we always remind our readers, you may always check our Site Map to be informed of any new site update (Opens a new Page). We are now introducing a new instrument that lets you be informed of any updates on the subjects you may wish to follow. It is called RSS Feed and it comes to you at no cost without the need to send anywhere your e-mail address. This concern was reflected in a note by a reader, see Testimonials further down the page.
We would like to urge you to subscribe to our Welding Advisers RSS Feed (or Site Blog as it may be called) by following the instructions on any page of our website. You need to subscribe just once, with your preferred provider. After you subscribe, by looking at "your" page (as displayed by your provider), you are able to quickly browse through title and description of any new item of ours, and then to decide if in fact you wish to see the item involved. We would like to be informed if you use and like this new tool.
Let us have your input in writing, by clicking here to send us Your Questions and Feedback.
9 - Short Items 9.1 - Amorphous metals, also known as metallic glasses, do not exhibit crystalline structure as its formation has been suppressed by extremely rapid cooling solidification, higher than the critical cooling rate. In this form several alloys present useful mechanical properties and can be processed like plastic when handled as required. To obtain useful alloys with these properties a few principles are now well established, describing characteristics that permit to design favorable compositions. High strength, toughness and plasticity can be reached. Other fabrication processes alternative to casting are now available. They are similar to superplastic forming, by heating the metal in the supercooled liquid region and deforming it under moderate applied stress. 9.2 - Biomaterials or bio-compatible materials are substances used to manufacture prostheses, implants, and surgical instruments that are not rejected by human or animal tissue (skin, blood, bone, etc.). They can be natural (collagen, cellulose, etc.) or synthetic (metallic alloy, ceramic, plastic, and others). Dental crowns and contact lenses are examples of biomaterials. Employed in surgery or used for tools needed to examine the living body, and for repairing the insufficiency of a sick organ, materials must be biologically compatible with the organism. Metals, alloys, polyester and non-toxic materials may be easily tolerated by patients although they cannot completely integrate with living tissues. Hybrid materials are now researched that associate inert and living material created and grown by tissue engineering. 9.3 - Pulse Puddle Arc Welding introduces vibration in the welding puddle to improve weld quality and ductility, to reduce cracking and distortion, to provide higher welding speed according to the developer www.bonal.com 9.4 - The Seebeck effect occurs on wires of any two members of the thermoelectric series connected to form a circuit with two junctions. The presence of a temperature difference between the two junctions causes a small current to flow in the circuit. It is the scientific principle upon which is based the use of Thermocouples, essential tools of temperature measurement in industrial processes. 9.5 - Thermal Barrier Coatings (TBC) are employed to permit higher operation temperatures while protecting the base material of critical components of gas turbines and similar equipment. They usually consist of two layers. The first, called bond layer is a metal, intended to protect the base material from oxidation and corrosion and to provide a good grip of the next layer of thermally insulating ceramic material, notwithstanding different coefficients of thermal expansion. The ceramic coating is generally yttria partially stabilized zirconia (YSZ), since this material has demonstrated its suitability for a range of demanding applications. Competing processes are available to provide acceptable coatings. 9.6 - Thermography or Thermal Imaging uses the representation of the thermal condition (transient or steady state) of a body, recorded on a medium sensitive to infrared radiation. Infrared cameras are usually employed to monitor equipment or structures that may need maintenance. The pictures are called thermographs. Abnormal heating can be detected, usually without disassembling. Non destructive testing techniques can use thermographic examination, if normal and faulty conditions display different patterns of thermal radiation absorbed or emitted. This technology can be used for solving a vast array of welding and brazing problems if proper equipment and methods are selected for monitoring or measuring the required variables.
10 - Explorations: beyond the Welder Green Chemistry Ocean Acidification Ultimate Paper Plane Radiation Shielding for Humans in Space Longevity Genes
11 - Contribution: Thermite Welding Thermite Welding is quite an old process used successfully for the joining and field repairing of rails in railroads and for other specialized applications. A Short Item note was published in section 9.5 of PWL issue 12 for August 2004. To see the note click on PWL#012 (Opens a new Page). It consists essentially of casting in a conformal refractory mold, held in place by mechanical means, the right volume of superheated molten steel obtained by an exothermal reaction. The rail edges are melted by the heat and form an alloy with the molten metal, solidifying then in the welded joint. The reaction is started by igniting a mixture of powders in a crucible located just above the mold. The powders consist in metal oxides, alloying metals, and metal reducing agents like aluminum or magnesium in various proportions. Chemical composition is one of the major factors affecting weld quality. Rail metal grade contributes to the final properties by its dilution into the weld. Different grades of rail steel have definite composition and mechanical properties. Conducting the Thermite Welding process correctly is much of an art requiring knowledge, skill, experience and workmanship. The success of the final outcome depends on the care deployed in every stage. Preparation, alignment, root opening, mold positioning, preheat, all these stages play an important part. Material quality with controlled low amounts of impurities and powder size, composition suitable to the actual rails, correct packaging, storage and preservation in dry conditions are essential ingredients. Adequate blending and loading of the crucible, controlling fluidity and final temperature by adding cold steel pieces if necessary, determining the exact tapping time to reduce the chances of slag or porosity inclusions are known to influence the microstructure and mechanical characteristics of the weld. Achieving the desired hardness and chemical composition to match those of the rails being welded is most important for adequate service performance duration. Special means are employed to retard the cooling rate from liquid state when specific microstructures are required. Hardness differences among the various zones and residual stress levels will depend on Post Weld Heat Treatments. Finishing operations achieve final dimensions and shape. Inspection is then performed to assess joint quality. Stricter cooperation between materials suppliers and railways authorities could improve results of this old process by using the tools of modern metallurgical investigation. An Article on this subject was published in the January 2006 issue of the Welding Journal at page 24.
12 - Testimonials Good morning,
On Wed Feb 01 21:23:40 2006, the following results were submitted from the "Form 5" on welding-advisers.com: From: M. Anderson (e-mail address withheld for security) Questions and Feedback : Thanks for the site. Just found it, via Google, and have been reading some plasma cutting and GMAW info. [...]some people hesitate [...] when they have to provide their email address, for fear of getting even more spam. We're some of those. [...], just the same, please don't pass our address around.
13 - Correspondence: a few Comments 13.1 - A few readers declared their availability for writing articles or notes of general interest in subjects they have deep knowledge of. We thank them all for their good will but we are still waiting for their contribution. Please, take your time now, write that note and send it. Do it. It will be a refreshing new voice, our readers will appreciate your effort. Thank you. 13.2 - A reader asked us to reconfirm our correspondence for permitting him to remove the block on his mail from our address. We complied per his request, but our letter bounced back. It was not allowed to pass, and we had no other way to inform him. Please arrange your terms directly with your provider. Do not ask us to perform extra actions.
14 - Bulletin Board 14.1 -WELDEX 14.2 - BEIJING ESSEN WELDING 14.3 - 17th Advanced Aerospace Matls. & Processes Conf./Expo 14.4 - Visit our WebSite Host: click on
See you next time... Copyright (c) 2006 by Elia E. Levi and welding-advisers.com,
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