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PWL, Issue #020-Manganese Safety Issues, Straightening with Heat, Welding Stainless clad Steel, HFRW April 01, 2005 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. Practical Issues, Creative Solutions
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.
You are urged to pass-along this publication to your
Date: April 2005 - Practical Welding Letter - Issue No. 20
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1 - Introduction 2 - Article: Manganese and its Safety Issues 3 - How to do it well: Straightening with an Oxyacetylene Torch Flame 4 - Filler Metals for Stainless clad Carbon Steels 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article: High Frequency Welding 8 - Site Updating 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contribution: Weld Maps 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction This Spring time issue of Practical Welding Letter is by now received by more than 1650 readers: we hope that most of you enjoy what you can read here and that it both satisfies and tickles your curiosity. Our first Article belongs to Health related subjects. It is remarkable that it was originated by a question from a reader, evidently busy with finding adequate answers to what has to do with his daily job. We are glad to be of help. For the Questions and Answers department we propose an old technique, long known and possibly already forgotten, that may help to redress warped items. Again another reader's question called this item to our attention. How do we weld Stainless clad Carbon Steel? Nothing misterious here, only careful application of sound principles, that it may be useful to refresh. Our next Article reviews the basics of High Frequency high speed continuous welding, for sure not devoted to the common job shop but nevertheless an important process for tube making. By the way, this process may be challenged in certain niches by the more economic applications of Laser Beam Welding. In the Site Updating department we point out our new Page of the Month: we just touch on the essential steps available to anyone curious to see the internal visual aspect of his/her test weld, by using some simple techniques borrowed from Metallography, the art and science used by advanced Metallurgical Laboratories. By limiting ourselves to common steel and low power magnification Macro sections we hope to provide easily implemented means to see the results of our welding efforts, and to improve on our results. We would like to urge all to try this out. In the Contributions section it is again another reader's question that spurred our dealing with the subject of Weld Maps, what they are and what are they used for. The other departments are there as usual for your information, we hope that you are interested. In any case you are again incited to ask for what actually bothers you, as you should know by now that your queries are always welcome. So click here to send us by e-mail Your Questions and Feedback.
2 - Article: Manganese and its Safety Issues Note: 1 - It is amazing that this Article on Health issues originated from the request of one of our readers. He actually works with an Insurance Company and is probably bothered by the subject. We welcome this opportunity because the feedback helps us provide information focused to real problems. Readers are urged to propose their own problems. Click here to send us Your Questions and Feedback. Note: 2 - This information is brought to the attention of our larger readership with a special word of caution for the self employed readers who, too busy with their day to day welding shop operation, might tend to disregard or overlook the requirements for a healthy work environment. They should not. Their Health is concerned. Manganese is a metallic element, quite abundant in the Earth's crust, present in content from 0.30 to 0.80% in most common commercial steels. It works as a deoxidizer and combines with sulfur to prevent hot shortness (crack formation upon cooling from the liquid state). In ironmaking, it is added to molten iron in the required proportion from one of several types of ferro-manganese of different composition. Manganese is present in higher content, around 13%, in a special alloy called Austenitic Manganese Steel. This is a nonmagnetic extremely tough steel having high strength, high ductility and excellent resistance to wear for service conditions that combine abrasion and heavy impact. Besides its effects on hardenability of certain steels of medium or higher carbon content, Manganese may increase the crack sensitivity of welded joints especially for steels with higher carbon content. Manganese is also present in alloys of copper, of aluminum and of magnesium. Manganese derived from food in tiny quantities is an essential element for the welfare and health of human beings. Although Manganese is not poisonous or carcinogenic (causing cancer) according to EPA (however this issue is highly disputed), it is considered harmful if swallowed or inhaled. Exposure to breathing excessive manganese dust can cause irritation of the lungs. Therefore regulatory authorities issued instructions for the maximum exposure values that should not be exceeded. There are various safety measures, including protective gear called Personal Protective Equipment (PPE) and other means to disperse the fumes away from workers, that have been put into place to avoid harmful exposure to Manganese dust or fumes. See: http://www.osha.gov/SLTC/personalprotectiveequipment/ Manganese lawsuits are available to people who consider their health having been impaired by excessive exposure to these effects because of negligence of the employer and inadequate implementation of the necessary preventive measures. A page from OSHA on dangers of exposure to Manganese Fumes is online at http://www.osha.gov/dts/chemicalsampling/data/CH_250200.html The American Welding Society (AWS) has issued the following documents: EWH-1 through 12 Effects of Welding on Health Vol. I through XII F1.1:1999 Methods for Sampling Airborne Particulates Generated by Welding and Allied Processes F1.2:1999 Laboratory Method for Measuring Fume Generation Rates and Total Fume Emission for Welding and Allied Processes The International Manganese Institute (http://www.manganese.org/OHESPolicy.php) has made a policy of an enduring commitment, among other purposes, to ensure that member companies are informed of the best occupational safeguard measures to better protect their workers. In their 2004 Annual Conference in Tokyo, eight presentations were given, including a report on Manganese exposure litigation in the United States. This report is probably available to interested parties.
3 - How to do it well: Straightening with an Oxyacetylene Torch Flame Q: - How can we straighten a warped beam? A: - You can use an oxyacetylene flame. The purpose is to introduce in the beam carefully planned tensile stresses to pull the beam straight. You know from our page on Welding Distortion that residual tensile stresses form because of local thermal expansion. The explanation is as follows. Stresses are due to volume changes with heating and to decreasing yield strength at elevated temperature. Metal subject to thermal expansion while heated tends to be compressed by the surrounding cool structure. The heated volume has lower yield strength at high temperature, and then it is easily upset to shorter dimensions. Upon cooling the same material tends to contract in all directions and is now stressed in tension by the attached cool structure which did not move appreciably in the process. By now the yield strength is again higher, at lower temperature, so that the upset material cannot regain its original dimensions. The result is the development of residual internal tension stresses in the weld. By selecting the convex portion of each bend and applying sufficient heat (in steel: to bright red) to a suitable amount of material, one can cause sufficient tensile stress to redress the beam. The careful selection of the location of heating is critical, and the amount of applied heat is what determines the success of the operation. The practice can be repeated for other areas nearby until the result is acceptable. One should take care not to heat the whole beam too much because that interferes with the purpose of straightening. What works for a beam works also for a surface presenting unwanted bulges. The principle is the same, to introduce two dimensional residual tensile stresses by heating up the convex portion of the deformed plate. A word of caution is necessary when dealing with stainless steel. One should beware of heating in the sensitization temperature interval. (See on this subject Stainless Steel Welding)
4 - Filler Metals for Stainless clad Carbon Steels How to weld Stainless clad common steel? Well, it just means correct application of well known principles. Cladding of Carbon Steel with a relatively thin layer of Stainless Steel provides an economic solution for different types of containers or process vessels that need a corrosion resistant material facing the corrosive fluid, while the pressure or the load of the structure can be sustained by a more economical material. In the past, before clad material was available, welding shops used to apply the stainless layer by laying short lengths of stainless steel strips on the internal surface of the fabricated part and slowly welding them one by one. Another method was surfacing the base metal by depositing a continuous stainless steel weld bead with a stainless electrode, by some mechanized process like Submerged Arc Welding. But since Stainless clad steel is available, either as Roll Bonded material or Explosive Welded plates, the problem is how to join the layered material on itself edge to edge. The welding procedure has to take into account the fact that modifying the composition of either of the steels by welding, through dilution with filler material, may produce unwanted structures prone to cracking. Therefore the following method is recommended. A generous bevel is machined on the carbon steel side of the composite base metal and then welded with a suitable electrode taking care not to reach the stainless steel layer with the weld bead. The joint is then gauged (ground or machined) from the stainless side, to reach the root of the carbon steel weld. The stainless steel weld deposit on the carbon steel must be made with a filler material of such alloy content that the dilution by the carbon steel will not produce a brittle bead. Suitable electrodes of type 309 or 312 produce weld beads which are partially ferritic, resistant to hot cracking. After having covered the carbon steel by surfacing (welding) it with the above electrodes, the remaining volume can be filled with the ones that where used or, if preferable, with 308, 316 or 347 types. If the layered steel has to be joined to solid stainless steel, the bevel of the first has to be buttered (covered by welding) with 309 or 312 material and then welded to the stainless by any one of the suitable stainless electrodes.
5 - Online Press: recent Welding related Articles As announced in the previous issue of PWL, our article on From AWS - The Welding Journal and from NIST - National Institute of Standards and Technology from TWI Another Article of ours, unfortunately not available online,
was printed on Practical Welding Today of March/April 2005
under the Title:
6 - Terms and Definitions Reminder Brazing Stop off is a liquid, paste, powder or other material selected to prevent brazing filler metal to flow and stick on surfaces where it is not intended to be, outside the capillary space of the brazed joint. Chills or chill bars are fixturing elements, usually made of copper, intended to operate as heat sinks, to cool down rapidly the surroundings of a weld, in order to improve its mechanical properties by inducing the formation of a suitable microstructure. The Contact Resistance test is a standardized procedure used to determine the electrical resistance of interfaces. The test measures the effectiveness of cleaning procedures used for the preparation of aluminum alloys for resistance welding. The setup includes a pair of standard electrodes of definite dimensions (dia. 5/8", 3" spherical radius), clamping the aluminum sheet combination (before welding) under a static load of 600 lb. A direct current of 50 ma (milliampere) is made to flow between the electrodes, and the resistance is measured with a suitable instrument. Adequate cleaning should result in 10 to 200 microhms. Any higher or non steady results indicate that cleaning improvements are required. Dew point indicates the amount of moisture present in a gas or in a furnace atmosphere. It is the temperature at which moisture starts to condense. For certain processes it has to be limited to accepted values for best reuslts. Dressing is a maintenance routine to be regularly performed on copper alloy electrodes for resistance welding. It consists in restoring the surface geometry and cleanliness after a number of resistance welds as necessary to provide acceptable and consistent results. Intermediate operations with abrasive paper may be used to clean the electrode surface from pick up of contaminants. Numerical Control Joint Tracking consists in programming a welding path to be followed by a welding source (torch or high energy beam) by conventional microprocessor controlled equipment. The purpose is to deposit the weld bead exactly where required. The control may be supplemented by correction if a vision or electronic sensing instrument is employed. Purging consists in eliminating air (and Oxygen) from the immediate surroundings of a weld, either by a vacuum or by streaming an inert gas for avoiding weld oxidation and degradation. Solving the problem may be difficult if the workpiece presents numerous air pockets. Salt bath brazing or Dip brazing is used for aluminum alloys. It provides concurrent heating and fluxing of the whole assembly in a bath of molten flux. The brazing filler alloy is either preplaced or available as brazing sheets, where the aluminum brazing alloy is roll bonded unto the aluminum base metal. The liquid displaces air, provides buoyant support and uniform heating.
7 - Article: High Frequency Welding Two processes use high frequency electric power with economic advantages, generally for high speed industrial continuous welding processes for tubes, pipes or closed roll formed profiles manufactured from coiled metal strips. In the first one, called properly High Frequency Resistance Welding (HFRW), heating is produced by resistance to the flow of an electric current applied by sliding contacts to the surface of a strip, roll formed into a tube or pipe, or other closed profile, by a pair of electrodes placed on either side of an open V formed by the converging edges to be welded together. The current flows from one contact to the meeting and welding point at a short distance, and to the other contact symmetrically placed, along the sides. Welding is performed by powerfully squeezing together and upsetting the two heated strip edges using properly shaped rolls. The result is some kind of forge welding, where molten metal drops, if at all present, are pushed out in the upset flash forming on both sides (inside and outside) of the tube together with any other oxidized or contaminated surface layer. The flash has to be shaved if necessary by proper tools. High Frequency current tends to flow at high densities along surfaces (skin effect), therefore heating is most effective for the above kind of applications. The other process, called High Frequency Induction Welding (HFIW) differs in that the current is transmitted through an induction coil, generating in the strip edges eddy currents rapidly heating up the region to the proper temperature. Squeezing and forge upset welding follows as before. This procedure is preferred if the strip surface condition cannot ensure positive and continuous current transmission through sliding contacts. Carbon steels, stainless steels, aluminum, copper, brass, and titanium have been successfully High Frequency welded into closed type profiles. Reactive materials may need inert gas shielding. Recently a competitive fusion process, Laser Beam Welding, has been used for this type of high speed manufacturing. The economics of these different methods must be carefully studied and compared for any given situation. A variant of the above is being used for welding together the end of one strip to the beginning of the next one. A special setup is needed to set the heating current across the strip ends, brought to contact under low pressure. Proximity conductors are used to induce heating by eddy currents along the joint. Again when the temperature is right the edges are pushed forcefully one against the other, producing the required upset welding. High Frequency Welding is well suited for continuous high speed welding and for a large range of product sizes and materials. Quality is generally remarkably good in that potentially harmful contaminants are squeezed out in the upset flash and the weld itself, devoid of cast structures, is hot worked to better properties. These processes cannot be economically adapted to low speed interrupted welding. Also one should note that High Frequency has the potential to disturb radio communications and proper functioning of nearby computers or sensitive instruments.
8 - Site Updating The newly added Page of this Month is dedicated to provide information for setting up the simplest possible metallographic capability in any welding shop. By limiting the activities to steel only we were able to suggest simple means to make possible macrographic (that is: visual, at low power magnification) examination of cross sections of welded test pieces. We believe that any welded production should be assisted by a metallurgical laboratory for providing evidence on the actual quality of the performed welds. Demonstration of such a capability would be a most convincing marketing asset and argument. However, for those situations where this professional assistance is not readily available, we would recommend to set up the limited facility described, in order to be able to observe, at least partially, the quality and the consistence of production. For reading this new article click on the Weld Macro page. As usual we recommend to our readers to see what is new in our Website by visiting periodically the Site Map.
9 - Short Items 9.1 - Electrical Discharge Machining (EDM) is a method for contour cutting of metal blocks or for producing therein holes, slots or irregular cavities. It is performed by controlled removal of material. This is done by high frequency sparks that melt or vaporize the metal locally along a moving line described by the electrode wire or tool. Therefore hardness of metals like heat treated tool steels does not represent an obstacle. The spark discharge occurs by pulsed direct current, between the tool and the work (the electrodes) through a controlled spark gap. Both electrodes are immersed in a dielectric liquid that permits the spark discharge to occur. The surface obtained is the result of all the contiguous molten spots, therefore it is rough and covered by a thin irregular remelt layer. Many applications require the further elimination of this layer which has unfavorable metallurgical characteristics. That is done by mechanical means like grinding to remove imperfections that may favor the appearance and propagation of cracks in operation. 9.2 - Load cells are electro-mechanical devices used to measure forces like weight or thrust. They are therefore called Force Transducers, usually built as slightly deformable sensors that detect minor elastic deformations. Load cells exist in various forms and sizes to cater for the most different applications. They are usable in a definite force range where their operation remains elastic with suitable accuracy. They usually employ Strain Gages (mentioned in the article at 9.5 of PWL #15 that can be reached by clicking on PWL No. 15) as sensors generating an electrical signal to instruments calibrated to provide results directly translated in the required units of (force) measure. 9.3 - Optical Pyrometry is defined as the determination of the temperature of a source by the detection of its incandescent brightness. It deals with non contact temperature measuring techniques based on the brightness of glowing bodies. It is used for determining the surface temperature of flames, of molten metals and even of operating turbine engines. The actual optical radiation emitted by a glowing body strongly depends on the emissivity of the surface, a property that describes the brightness of a target at a given temperature. 9.4 - Photoelasticity is an optical method for evaluating the magnitude and distribution of stresses, using a transparent plastic model of a part, or a thick film of photoelastic material bonded to a real part. Photoelasticity involves applying a certain stress state to the model and using the induced birefringence of the material to examine the stress distribution within the model. The magnitude and direction of stresses at any point can be determined by examination of the fringe pattern, and related to the studied structure. 9.5 - A thermocouple is a device for measuring temperatures. It consists of two dissimilar metals or alloys wires welded together at one end and connected to a voltage measuring instrument at the other end. More accurate results are obtained with potentiometers. When one junction is hotter than the other, a thermal electromotive force is produced that is roughly proportional to the difference in temperature between the hot and cold junctions. Different metal combinations are suitable for different temperature ranges. Tables are available for translating the read voltage values to temperature. Ambient temperature compensation is needed for correct results. 9.6 - Traceability is the capability of tracing back the origins of materials and processes of a manufactured item. To guarantee the application of this quality requirement, a set of administrative procedures must be prepared and followed by all involved according to precise rules. Implementation of traceability means positive identification of the original batch of materials supply with all relative production data and characteristics records. All intervening processes and quality control data, including equipment, instruments, personnel and calibration details must be reported and recorded, and must be available for inspection and audit purposes. Also the materials and instruments used for analysis or calibration must be with demonstrated and documented reference to approved national standards.
10 - Explorations: beyond the Welder A WWF Project Spring Photos Technology and Human Responsibility SpaceRef, Future Technology, Interstellar Travel International Manganese Institute
11 - Contributions: Weld Maps We are glad to be able to give specific answers to a focused question proposed by a correspondent who asked us what is exactly a Weld Map and how it is used. It appears that he had been requested to provide some, but was not sure how to go along with that. As this subject might be of interest also to other readers we propose hereafter some more details to explain and clarify the issue. Some drawings of complex welded structures may easily contain instructions for many tens or even hundreds of single welds, indicated by using welding symbols as per AWS Welding Symbols Chart A2.1. There is obviously a need to refer to each one of the welded joints individually, especially when establishing requirement notes that apply to all the welds of a group defined by material, thickness, joint type, procedure etc. The identification system consists in assigning a unique designation number to each weld, usually enclosed (for easier location) in a common shape like a circle, an ellipse or other. The Weld Map attached to the drawing is an ordered list of all the welded joints. For finding on the drawing any one weld from the list there is generally a coordinate system (A, B, C,...1, 2, 3, ...) along the margins that helps locating the specific weld amid all other ones. A note is added, specifying materials, filler metals, type of joint, preparation, weld dimensions, weld procedure No., special instructions like preheating or Post Weld Heat Treatment etc. The sequence requested may also be specified if important and notes may be added requiring that certain welds be performed before specified other ones. The Weld Map may be used for establishing a work plan, by assigning certain welds to welding teams and holding them responsible for the quality achieved. As a check list the Weld Map is used to make sure that no joints were omitted or overlooked in the actual production program. Special Quality requirements for visual and non destructive inspection make use of the Weld map as a commonly understood method of referring to each of the joints for reporting on the results of the examination and on the final decision. That is also needed for providing repair instructions to the fully identified weld joints. As a reference you may look online at the following document: WELD RECORD PACKAGES AND PIPING TESTING PACKAGES http://www.inel.gov/dmcs/prd-5010.pdf In particular you may notice the following paragraph: "4.6.1 - The weld map shall be maintained on Form 432.43, Subcontractor/Supplier Weld Map, or an approved equivalent. The weld map must provide adequate information to provide traceability between the actual weld and the weld history record." A copy of Form 432.43 may be obtained by contacting directly the Idaho National Laboratory at
12 - Testimonials From: Mark Clark 'res219ng@verizon.net'
Very Good information! Thank you very much. Mark Clark
From: Ben Gross 'b.gross@wtia.com.au'
Thank you very much Elia;
13 - Correspondence: a few Comments Occasionally we may meet the most strange questions. One received recently was: "You know MIG Brazing process. I want detail about Brazing process this." Another one asked for instructions for "...welding galvanized tin." Needless to say that these and similar expressions are exercises in futility giving away the notion that the inquirer has no idea of what he/she is saying. (Maybe a joke). But even if the inquirer knows the matter, it happens sometimes that most necessary details are not disclosed: if the question is not focused, the answer is a shot in the dark, unless a list of conditions is used to qualify the answer. So please formulate precise questions. As always it would be important to state the purpose of the inquiry, and to undertand what the receiver is going to do with the answer. I would like to read also a short introduction of the inquirers themselves explaining their connection to the problem. You will understand why I am put down by letters without greetings and signature. Anyhow we welcome your proper inquiries. Click here to send us Your Questions and Feedback.
14 - Bulletin Board 14.1 - The 2nd IAS/AWS Rio de la Plata Meeting on Welding will be held on Thursday, November 10, 2005, at the “Hotel Colonial – San Nicolas – Argentina” First Call for papers: 14.2 - 16th AeroMat Conference & Exposition 14.3 - I think I cannot do a better service to the few readers who followed me till the very end of this new issue of Practical Welding Letter than by proposing you take a look at what other people, self described as normal and ordinary, did by building a business with the help of a tool kit called SiteBuildIt! Many of our readers already have websites but they could possibly improve them if they only knew how to. Other persons might start thinking of building one. See what Dr. Ken Evoy, the Founder and Owner of this amazingly successful little company, has to say to you, the occasional visitor: "As a doctor, I fondly remember our bulletin boards full of photos and thank you cards from patients whose lives we'd saved in the Emergency Room. It was the same in the neonatal unit. I always felt that our Case Studies site was like that..." Click on the pictures of that very special bulletin board and read the actual stories presented by real people. You could learn a lot just by browsing through the exceptional resources and proofs offered by our Site Host at no cost to the visitor. If you want only a short glimpse, go for the Quick Tour. You will be amazed... And visit SiteSell's Home Page and when you are there click on the small RSS orange button. That will provide you with all the "SiteSell Sites Updates" which is "must-read" material, to stay up to date. Finally please note that the price of the whole SBI! toolkit was reduced, from the beginning of this year, to less than US$ 300! With the Full Refund Guarantee, that means you can try the whole package at no cost...! While you are at it, ask experienced SiteSell Affiliates your Questions. They will be happy to answer them. Good Luck!
See you next time Copyright (c) 2005, by Elia E. Levi and welding-advisers.com, all rights reserved
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