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PWL#111 - NDE and Weld Repair of CSEF, Guided Bend Test for Al, Al Filler Metals selection, Qualif. November 01, 2012 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#111 NDE and Weld Repair of CSEF (Creep-Strength-Enhanced Ferritic) Steels, Guided Bend Test for welded Aluminum specimens, Filler Metals selection for welding Aluminum Alloy 6005-T6, Welder Qualification, Promising Innovations for useful Applications, Material Identification(R), Repair Welding (R), and much more...
November 2012 - Practical Welding Letter - Issue No.111
The Mid October Issue of Practical Welding Letter, Bulletin 78, dealing with Resources on Pulsed Arc Welding, was not distributed by e-mail but it is available at Bulletin 78 or from the Welding Resources Page.
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1 - Introduction 2 - Article - NDE and Weld Repair of CSEF Steels 3 - How to do it well: Guided Bend Test for welded Aluminum 4 - Filler Metals for welding Aluminum Alloy 6005-T6 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: Welder Qualification 8 - Site Updating: Material Identification(R), Repair Welding (R) 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Promising Innovations for useful Applications 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board (Sponsored Links)
1 - Introduction This 111th issue of Practical Welding Letter opens by reporting on recent research performed by EPRI, in constant search for improvements in the performance of special steels used for critical components in power generation plants. The research is challenging because performance depends on subtle changes in microstructure, occurring because of fabrication by welding, of repairs and of long time service conditions at elevated temperatures. While the studies based on metallographic investigations are the most informative, these are destructive tests, at least on portions of the material to be examined. The challenge is to develop indirect methods based on new and advanced non destructive examinations, capable of gathering precise information on the most endangering conditions, without resorting to cutting into the material. The race is still open, and sometimes frustrating, as reported in the article. The nex subject is important if you need from time to time bend testing to qualify aluminum welds. Then you could benefit from the note reported here. It is informative insight from a renowned expert on aluminum welding. In the section just following the presentation above, the same author explains the criteria to be used for selecting suitable consumable filler metals for welding aluminum. The process is explained in some detail, to the effect that selection is variously conditioned by additional data. Information on further usage in service and on additional thermal treatments if any, must be gathered and evaluated before making the final consumable choice. Welder Qualification should be fully understood before bidding for demanding jobs. Profitability should be evaluated thoroughly before undertaking costly obligations. However, once suitable qualifications are achieved, the contractor disposes of enviable assets likely to pave the path to more profitable enterprises. Information on revised website pages is given in section 8 further down. This month Welding Advisers show the updated pages on Material Identification(R) and Repair Welding(R). Especially those working on repairs should make sure they ascertain the exact material they work with, to avoid mishaps. The other columns appear regularly at their place. By now you should know how to find what you need. Besides the Search function from almost every Welding Advisers page, you can browse the Site Map or the Index Page. Articles from Practical Welding Letters can be found in the Welding Topics page. Links to the PWL complete list is available from the Index of Past Issues of PWL. The subjects treated in the Mid Month Bulletins are listed in the Welding Resources page. Please use the Contact Us form to send your comments, feedback or questions. 2 - Article - NDE and Weld Repair of CSEF Steels The subject of this Article was dealt with briefly in two notes (4 & 7) published in Issue 83 of Practical Welding Letter for July 2010. Links to relevant online sources is available in Bulletin 51, appended past the end of the above publication. To reach the documents, click on PWL#083. The successful increased use of Creep-Strength Enhanced Ferritic (CSEF) Steels in the manufacture of hot, pressure retaining components, depends on close monitoring of metallurgical damage developing in due time in critical elements. Typical and most known of these materials is Grade 91 (modified 9Cr-1Mo) alloy steel, used in the boiler tubes, piping and headers of fossil-fuel-fired and combined-cycle power plants. An Article on this subject, written by Researchers at the EPRI (Electric Power Research Institute), appeared on page 20 in the October 2012 issue of Advanced Materials and Processes, an ASM International publication. The challenge facing operators of power plants, and the metallurgical community at large, is to keep track of the material damage occurring in service, to be ready for intervention on specific components just before failure. Damage managing is necessary to prevent catastrophic explosions endangering human lives and to avoid sudden shut downs implying unbearable economic cost. The Authors explain that three kinds of information must be obtained:
This cumulative information would provide a measure of the residual life of the component up to failure and permit to take logical actions to minimize the loss. The Authors continue explaining that it is important to identify the mechanism responsible for the damage, and to determine the root cause of the damage. This analysis is critical because understanding the reasons for accelerated damage would permit to take remedial action to minimize future risks. Current damage assessment requires continuous monitoring by non destructive examination (NDE). To determine the degree of damage required to cause failure, analytical or experimental techniques must be used. The decisions needed to optimize an operation depend heavily on successful answers to the above questions. Classic non destructive testing methods answer only in part to critical questions involving metallographic changes like accumulation of creep voids in the bulk, before the appearance of surface indications like microcracks. Improvements in current techniques and application of new ones are actively pursued by researchers. Special ultrasonic testing techniques like phased array and time-of-flight are studied for their higher sensitivity that can detect clouds of damage. Acoustic Emission is explored to determine if creep damage can be identified. Other methods are briefly reviewed in the Article but no breakthrough has been announced yet. Continuing research is required for improving the tools permitting successful monitoring of existing and future structures of CSEF Steels. Interested readers are urged to seek the original Article quoted above. For more information on EPRI research projects see the article Links to Online references are available in PWL Bulletin 51 mentioned in the first paragraph of this article.
3 - How to do it well: Guided Bend Test for welded Aluminum In an interesting Q&A Note, published on the October 2012 issue of the Welding Journal at page 18, Tony Anderson explains basic requirements for bend test. That follows an extensive discussion, reported hereafter in section 4, on how to select filler metals for application in welding aluminum alloys. The Author explains that the usual plunge type fixture used for steel bend test specimens, is not recommended for testing welded aluminum specimens. That is because, due to the properties of the aluminum heat affected zone, using the plunger may cause the specimen to bend sharply and break. Instead of that, a suitable wraparound guided bend test fixture forces the test specimen to bend progressively around a pin. All parts of weld and heat affected zone are bent around the same radius of curvature and, therefore, are submitted to the same strain level. The Author stresses also two other most important points. One is the maximum radius permitted by codes on the corners of the specimen. That is usually up to 3 mm (0.125"), and should be adhered to, as sharp corners invite failure. The other is the correct bend radius stipulated by AWS D1.2 - Structural Welding Code - Aluminum that varies with materials and condition (as welded or annealed), and the specimen thickness, that should be as required before performing the bend test. Annealing, if required, should be performed as specified in the code. Readers facing problems in meeting bend test requirements in welded aluminum specimens, are urged to seek the original article quoted above. 4 - Filler Metals for welding Aluminum Alloy 6005-T6 The question that started the article quoted in the section above, referred to a very specific case where the inquirer, that had to qualify a Welding Procedure Specification (WPS), failed to meet the bend test requirement and asked if the selected filler metal (ER4043) was at fault and alloy 5356 should be preferred. The Author, Tony Anderson, not knowing the details of the process nor the application, explains extensively the guidelines that direct filler metal selection. He lists the questions, exposing details of the application and of the intended welding process, whose answers will influence the choice. Starting with the alloy designation that must be known, he proceeds to inquire on service temperature [if higher than 150°F (66°C)], on post weld heat treatment if any, on importance of shear strength, ductility and toughness to part functionality, and on final anodizing process if specified. The reasons for selection of suitable filler metals are then discussed in detail in the article. Reading, understanding and memorizing the explanations of the original article is highly recommended. Here only a summary is presented. For welding alloy 6005-T6, filler metal 4043 is recommended when:
Conversely filler metal 5356 is preferred when:
Intermediate conditions would force the adoption of compromise solutions. This summary cannot compete with the richness of information included in the discussion of the original article (quoted in the above section), that is highly recommended to all interested readers. For suggestions on additional selections of filler metals suitable for welding different aluminum alloys not covered here, readers are referred to the article published (4) in PWL#004. 5 - Online Press: recent Welding related Articles GM unveils welding technology to reduce vehicle weight, improve fuel economy
GM Aluminum Welding Breakthrough (Video) Portable Metaltek CNC weld preparation machine from ART for maximum equipment uptime Avoid These 13 Common Pitfalls in Process Pipe Welding Applications
High-speed pipe-facing machines: bevel in 40 seconds 6 - Terms and Definitions Reminder Arc Welding Deposition Efficiency is the ratio of the weight of filler metal deposited in the weld metal, to the weight of the melted filler metal, expressed in percentage. Brazing Technique represents the details of a brazing operation that are controlled by the brazer, within the limitations imposed by the prescribed Brazing Procedure. Cycle defines the duration of a periodic, recurring function (like electric voltage or current) going up to a maximum in one direction, back to zero and then to a maximum in the opposing direction, and back to the starting value. Drag Angle is the travel angle when the electrode (or gun, torch, rod or beam) is pointing to a direction opposite to the progression of welding. Electrode is a part of the electric circuit in a welding machine, terminating at the arc, base metal (in resistance welding) or at the molten conductive slag (in electroslag welding). Flame Spraying is a thermal spraying process where the heat source for melting the surfacing material is an oxyfuel flame. Metallizing is a nonstandard term used to describe thermal spray processes for surfacing substrates. Progressive Block Sequence is a program in which the joint is welded in sections of several passes from root to top, in a predetermined order, to control residual stresses and distortion. 7 - Article: Welder Qualification The proof of adequacy of a welder to perform acceptable work is a fundamental requirement of all codes. Specifications establish which specimen type is required for which welder qualification. Standard joints have been selected for qualification. For any given application, Processes, welding position, Materials and Thickness ranges have to be pinpointed in such a way that the applicable Code or Specification recognizes welder qualification validity for covering the requirements of the job at hand. Before taking the test, the welder must be given an appropriate Welding Procedure Specification (WPS) establishing, besides the specific selections (Material, process etc.) from the data listed above, also the consumable and the parameters to be used for the test. These are the instructions to be followed for the qualification test and, once qualified by demonstrating, through non destructive and destructive tests as specified, that all requirements are met, also for the manufacturing process covered by the said procedure. The governing document establishes which variables in the WPS are considered essential. If the work at hand needs a modification of the value of an essential variable beyond the limits covered by the qualification, then the modified welding procedure has to be requalified. The successful performance of a qualification procedure for a welder, is certified by an official document of an authorized representative of the organization conducing the tests, that certifies the occurrence of the examination and its positive results. Such a document is the welder's Certification and he/she becomes the holder of the Certified Welder status. The Certification has a given validity depending on the code or standard. It will expire if the welder does not weld using the qualified process for six months or more, or if the quality of his/her welding is declared unacceptable. The validity can be extended if the welder is engaged in continuing performing successful welding of the qualified type, provided this is recorded in a document called welder Performance Qualification Record (PQR), kept and updated by the employer's quality personnel. The answer to a specific query was published (3) on PWL#059. The website page dealing with this subject is available at Welding Qualification. Interested Readers are urged to seek further reading on this issue, in AWS Inspection Trends, Summer 2012, page 11, at: 8 - Site Updating: Material Identification(R), Repair Welding(R) The Pages of this Month are revised and updated issues of older files published long time ago. From the nonchalant sloppiness describing materials in queries submitted in certain correspondence received, it appears that not all practicing welders have a clear knowledge of the importance of material identification for the jobs they may have to work on. It should become a natural attitude, to acquire all needed information on the materials at hand. If there is any doubt that the paperwork available may not reflect the actual, physical material to be welded, then suitable procedures must be engaged to identify it, by describing not only its general composition but also its condition, usually determined by performing hardness tests. The page on Material Identification intends to provide orientation by describing practical means to be used to achieve the required confidence to perform the work with the right process and consumables. The other page on Repair Welding admonishes that, besides the identification of the materials involved, one should inquire the reasons for the failure one has to repair. That much is needed if the equipment to be repaired has to return to operate confidently, at least until a more thorough solution is provided. Those whose welding work consists in maintenance and repair, should at least become acquainted with the above two pages as they might provide them some benefit. They should possibly expand their knowledge even further, to improve their skills. To browse through the large amount of information freely available in the Welding Advisers website one can review the Site Map and the Index Page. One can also search by typing the requested terms in the box that appears in almost every page of the Welding Advisers website: that will include also the articles of the Practical Welding Letter, now at its 111th (this) issue. Questions, comments and feedback are always welcomed. Don't use Reply, use the Contact Us form instead. 9 - Short Items 9.1 - Creep-Strength-Enhanced Ferritic (CSEF) Steels are, according to the ASME Boiler and Pressure Vessel Code, Section IX, QW/QB-492 (Ref. 2), a family of ferritic steels whose creep strength is enhanced by the creation of a precise condition of microstructure, specifically martensite or bainite, which is stabilized during tempering by controlled precipitation of temper-resistant carbides, carbo-nitrides, or other stable and/or meta-stable phases. 9.2 - Dislocation is a linear imperfection in a crystalline array of atoms. Two basic types are recognized: (1) an edge dislocation corresponds to the row of mismatched atoms along the edge formed by an extra, partial plane of atoms within the body of a crystal; (2) a screw dislocation corresponds to the axis of a spiral structure in a crystal, characterized by a distortion that joins normally parallel planes together to form a continuous helical ramp (with a pitch of one interplanar distance) winding about the dislocation. Most prevalent is the so-called mixed dislocation, which is any combination of an edge dislocation and a screw dislocation. 9.3 - Electroslag Welding is a process that produces coalescence of metals with molten slag that melts the filler metal and the surfaces of the workpieces. The weld pool is shielded by this slag, which moves vertically up, along the full cross section of the joint as welding progresses. The process is initiated by an arc that heats the slag. The arc is then extinguished by the conductive slag, which is kept molten by its resistance to electric current passing through the electrode and the workpieces. 9.4 - Free Ferrite is formed directly from the decomposition of hypoeutectoid austenite during cooling, without the simultaneous formation of cementite. It is formed into separate grains and not intimately associated with carbides as in pearlite. 9.5 - Granular Fracture is a type of irregular surface produced when metal is broken. It is characterized by a rough, grainlike appearance, rather than a smooth or fibrous one. It can be subclassified as transgranular fracture or intergranular fracture. 9.6 - Infrared Spectroscopy is the study of the interaction of material systems with electromagnetic radiation in the infrared region of the spectrum. The technique is useful for determining the molecular structure of organic and inorganic compounds by identifying the rotational and vibrational energy levels associated with the various molecules. 10 - Explorations: beyond the Welder Is Homosexuality a Choice? U.S. Government Has Little Authority to Stop Unsafe Cosmetics Nature Videos Antiscience Beliefs Jeopardize U.S. Democracy The Exoplanet Next-Door: Astronomers Discover World in Nearest Star System 11 - Contributions: Promising Innovations for useful Applications 11.1 - Galfenol, composed primarily of gallium and iron, is a new material with a unique set of material properties. It changes shape when subjected to a magnetic field. That interaction allows Galfenol to be used as a vibration-based energy-harvester. An introductory presentation states that "the combination of magnetic and mechanical properties could lead to the development of active motor mount technology, creating an environment that actively senses and cancels out motor vibrations, effectively creating a silent motor". Unfortunately no information is offered relative to the physical principles that explain such interesting properties. See the Ames article at: 11.2 - An endless pipe to be manufactured and delivered from a truck. The new pipe consists of a central layer of lightweight plastic honeycomb, similar to that used in the aerospace industry, sandwiched between layers of resin-saturated carbon fiber fabric. With much less connections than a regular pipe of concrete or steel, joint-free for extremely long sections, it can be manufactured on a mobile pipe-laying truck and delivered right in the trench. No examples of practical applications are presented, with actual comparison of capability, characteristics and economical advantage. See the introductory article: 12 - Testimonials Name: Thomas Wooler Thank you for taking the time to respond to my question. I will definitely take your suggestion into consideration. Thank you again. Tom Wooler
Name: John Lee Hi Elia, Kind Regards, John Ge 13 - Correspondence: a few Comments Corresponding with readers is an interesting experience, although sometimes ungrateful. I know that not all my answers can hit the mark, solve the problem or provide savings or gains. I only try to do my best. I come through all sorts of requests. It is a rare occasion, that one where the inquirer knows enough about his/her problem, to be able to ask pertinent questions while at the same time providing all needed information. I have generally sufficient patience to understand that some of those who ask may be so far from the matter, not to know that their question is unanswerable, at least if based only on the evidence they provide. No problem with that. I like to give answers if I can, and I would like that the addressees get the opportunity to learn a bit, even if I cannot solve completely their problem. Given a second chance and more details I might be able to come up with a more useful answer. Most of times I get no reward for my labor but I have no regrets. I do that for myself, nobody compels me to spend my time researching a subject and formulating an answer. I would be glad to get a sign of acknowledgment, though. Is that asking too much? What puts me down completely is the total and absolute lack of any reaction whatsoever, that unfortunately occurs from time to time. I understand that accidents may happen, and that people may forget. Maybe you don't give a damn. 14 - Bulletin Board 14.1 - FABTECH. 14.2 - ISTFA/2012 14.3 -
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