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PWL#083 & 083B - Bimetals, Hydrogen Furnaces, Power Plant Equipment, Heat Treatment, Straightening July 01, 2010 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#083 - Bimetals, Safety in Hydrogen Furnaces, Filler Metals for Power Plant Equipment, Field Heat Treatment of Pipe Steels, Flame Straightening a Pipe Distorted by Welding, Cold Spray, Resistance Brazing, Resources on Creep Resistant Steels and more... DON'T USE REPLY to send us your messages! Use Contact Us instead.
and Mid July Bulletin
Please be advised that the Mid Month Bulletin is now integral with the regular PWL publication. You will find it further down, past the end of this Practical Welding Letter. Important AnnouncementFor assembling at no cost your own Encyclopedia Online, Get Both Now at 20% Discount!Please be advised that the above Discount will be soon discontinued. Enjoy it now while it lasts!
1 - Introduction 2 - Article - Bimetals 3 - How to do it well: Safety in Hydrogen Furnaces 4 - Filler Metals for Power Plant Equipment 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Field Heat Treatment of Pipe Steels 8 - Site Updating: Cold Spray, Resistance Brazing 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Straightening a Pipe Distorted by Welding 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board (Sponsored Links) This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. You are urged to pass-along this publication to your friends, if you like it, and if you want to help them. If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple. Note: References to articles or other documents are given here in one of two forms. If the links are "live" (usually underlined or otherwise highlighted) they are operated with a click of the mouse. If they are URL's (Uniform Resource Locator), which is the analogue of an address, they begin with "http://..." or "www.". These are not live and must be copied and pasted entirely into the browser (after having been selected with the mouse or otherwise). If they are long they may be displayed in two or more lines. In that case one has to care that the URL be copied completely in a single line without any space, and Enter.
1 - Introduction Here is the 83rd issue of Practical Welding Letter and, appended at its end, the Mid Month Bulletin No. 51 for July 2010, dedicated to Resources on modern Creep Resistant Steels. This publication opens with an introduction to Bimetals. Their manufacture is some form of joining or welding but, once made, they are fixed in place, generally in thermal sensing devices, by mechanical means, because heating for welding can only impair their peculiar properties. Then important safety issues are summarized, concerning the operation of hydrogen furnaces. In practical cases a search should be done for binding regulatory documents and Fire Fighters should be given the opportunity to check if the accident prevention measures adopted are adequate. The next section introduces filler metals used for creep resistant structures. The search for suitable filler metals is only one important subject to be studied when preparing the stages needed for building creep resistant structures. The selection of base material may need study at least of the References presented in the appended Bulletin. The design of welded details, the development and qualification of adequate Welding Procedure Specifications and precise heat treatment instructions, as explained in section 7 further down, must all be dealt together as a whole program. In the Pages of the Month added recently to the website, one can find an introduction to Cold Spray, a coating process with unique advantages derived from Thermal Spray, and an explanation of the particular characteristics of Resistance Brazing, a brazing process using heating from current passing through the electrodes and the joint. I am pleased to publish a note kindly contributed by John P. Stewart on Flame Straightening a Pipe Distorted by Welding. The other usual sections can be found at their place. Readers already know that questions, comments and feedback are welcome. Please use the form available in the page on Contact Us. Please note that after the end of this issue, you will find the Mid July Bulletin rich with
references and links to important sources of knowledge on the subject of Creep Resistant Steels.
2 - Article - Bimetals Single bodies including two metals joined together to display specific behavior are called Bimetals. A thermostatic bimetal in the form of strip or sheet, is a composite material made of two metallic layers, permanently bonded together, with different coefficient of thermal expansion (CTE). The relative differential expansion of the two component materials exposed to temperature change, causes internal stresses to the structure, generating a deformation seen as a change in curvature capable of performing a mechanical action. This change in the amount of bending in response to a temperature change is a fundamental property of all thermostatic bimetals. This property is employed in thermostats acting as circuit breakers for opening electrical circuits. Thermometers use the bimetal to drive a pointer in front of a scale indicating the actual temperature of the sensing element. Conductive thermal controls can be built to suit a wide range of service conditions due to extreme versatility permitting to select the most appropriate bimetal for any application. A completely different application of bimetal, that does not exploit difference in CTE, is mentioned for blades of band saws and reciprocating saws. The purpose of using bimetal welded construction is for saving the more costly material. A Strip of high speed steel, where the teeth are milled, is bonded, along the side of the thickness, by electron beam welding or by laser beam welding to another strip of high-strength carbon steel. One of the ways to produce bimetals was indicated in my page on Explosion Welding and also in a short note in PWL#009. To weld together incompatible materials one can use bimetal transition parts, to be prepared for the specific application, joint by any suitable solid state process. This method was shown in my page on Weld FAQ and also in a short note published (3) in PWL#064.
3 - How to do it well: Safety in Hydrogen Furnaces The Hydrogen protective atmosphere has many useful applications in furnaces for metal processing, because of the reducing properties of this light gas. It is therefore widely used for bright annealing processes and for brazing stainless steels and nickel alloys. However it has a number of safety issues because Hydrogen gas at 1 atm is flammable in the concentration range 4–74% (volume per cent of hydrogen in air) and is explosive in the concentration range 18.3–59% (volume per cent of hydrogen in air). Therefore precise procedures must be followed when starting up and when shutting down, because it is in those transition periods that air may find a way to enter the furnace and form an explosive mixture with hydrogen. Security alarms and features should inhibit the start of any operation if the gases are low in volume and/or pressure in their respective containers, or if any of the valves is found faulty. Leaks from the Hydrogen line are particularly dangerous and therefore frequent checks should verify their complete absence. Hydrogen sensors must be used for rapid detection of hydrogen leaks. The air present in the furnace space must be removed before admitting Hydrogen gas. That is done by purging the furnace with an inert gas, usually nitrogen. Depending on the furnace build and function (batch type or continuous) a slight overpressure will always be maintained to avoid air leaking in. Hydrogen excess and that portion expanding due to heat, will be vented at the highest point and lit with a pilot flame to burn quietly in air (producing drops of water). Also at shut down, the inert gas is admitted to displace Hydrogen, heat is removed and the furnace is let cool down. Only then doors are opened and air is admitted, to unload the treated parts. The security issues to take care of are non programmed black out occurrences (interruption of electricity flow), interruption of cooling water flow, if used to cool down gaskets and doors, interruption of Hydrogen gas supply or sudden loss of availability of purge inert gas. A spare inert gas container must be easily accessible and operational with a few valve manipulations. For each of these emergencies it is imperative that automatic shut down procedures step in without manual intervention and overtake any other standard operation. The automatic planned shut down must include positive electric power interruption, positive hydrogen flow interruption, and admission of inert gas through a normally open valve (that opens when power goes off). As accidental explosions may be extremely dangerous, one should have in place back up systems, a thorough maintenance plan of periodic equipment tests, and a good training program frequently rehearsed. If properly planned, executed, maintained and controlled, hydrogen furnaces are not any more dangerous than other industrial equipment and can provide essential contribution to production facilities. See: A short note on Electrolysers, a possible source of Hydrogen gas, was published (11) in issue 33 of Practical Welding Letter for May 2006.
4 - Filler Metals for Power Plant Equipment The following publication provides an overview of many of the filler metals used in the construction of power plants, with special emphasis on the European experience. Welding filler metals for power plant engineering (20 Pages) It should be appreciated that selecting filler metal cannot be undertaken in abstract but must be based on thorough knowledge of the new creep resistant steels and on the requirements of the construction Codes applicable for the specific piece of equipment considered. Please be advised that also the article published further down in section 7, has direct connection with materials and welding for power generating equipment. All the different aspects treated here have a bearing on the understanding of the complexities of the issues and on the practical problems that must be solved for successful project realizations. Although good understanding of these matters requires an adequate basic preparation in metallurgy, the fundamental concepts are accessible to anybody curious enough to stay on the page until the general concepts are becoming clear. Therefore, in the Mid Month Bulletin No. 51 appended to this issue of Practical Welding Letter, an updated List of References is found, useful for studying or refreshing essential knowledge on Creep Resistant Steels. First in the list appear articles with General Information, not requiring too much prior metallurgical knowledge. Then come articles referring to Metallurgical Research. The subject seems interesting enough even for readers not actively engaged in design or construction of equipment for power generation. Readers are invited to browse through the List for their own instruction. Comments and Feedback will be appreciated. Please use the usual Form in the Contact Us page.
5 - Online Press: recent Welding related Articles Orion Spacecraft Takes Shape High-frequency electric resistance welding: An overview Download your copy of WELDING MARKETPLACE Superior for Stainless: High-Speed Pulsed GTAW
Robotic Pipe Welding (3 pages)
6 - Terms and Definitions Reminder Consumable electrode is a conductor that provides filler metal. Dip Feed is a process variant for Gas Tungsten Arc Welding, Oxyfuel Welding and Plasma Arc Welding in which filler metal is intermittently manually dipped into the weld pool. Electrode Tip is the end of the resistance welding electrode contacting the workpiece. Ferrule is a ceramic ring that surrounds the stud base in stud arc welding, to retain the filler metal and insulate the arc. Gas Tungsten Arc Welding Torch is the device that holds the non consumable electrode, supplies electric current, provides shielding inert gas, directs the arc and controls its length. High Pulse Current in pulsed welding is the high level current flowing during the high pulse time to provide the high heat pulse. Induction Work Coil is the secondary loop inductor used to heat the workpiece for welding, brazing, soldering or heat treating. Joint Tracking is the automatic function that follows the joint actual position during welding and corrects the position of the welding source (electrode, electron beam gun or laser gun) to place the weld in its proper location. Low Pulse Current in pulsed welding is the low level current flowing during the low pulse time to provide the low heat pulse.
7 - Article - Field Heat Treatment of Pipe Steels An Article on the subject described in the title above was published in the June 2010 issue of The Welding Journal at page 46. Field heat treatments have become a critical aspect of weld performance with the increased use of steels P(T)91 and 92 for demanding applications. These metals pertain to a relatively new class of materials called Creep Strength Enhanced Ferritic (CSEF) Steels. See the Mid July Bulletin appended at the end of this publication, for links and References to sources providing essential information on these materials. The need for the use of steels with improved creep rupture strength derives from the higher steam temperatures and pressures required to achieve increased thermal efficiency of fossil fuel-fired power-generation plants. These steels have favorable performance factors and some beneficial installation advantages but need particular attention to heat treatment requirements both during initial fabrication and while performing post welding heat treatments (PWHT). With increased use and practice, it dawned upon those involved, that heat treatments play a major part in the success (or the failure) of the applications, and that up to 90% of reported failures were attributable to improper heat treatments. To master the complex planning, executing and monitoring the precise heat treatments prescribed by Recognizing that the correct heat treatment processing plays a critical part in the success of the whole project, suitable means must be employed to assure the application, monitoring and reporting of uniform heating and temperature control throughout the whole section of the pipes. These may consist in precise descriptions of the heater bands to be employed and of their prescribed disposition to wrap completely the construction, and of the number and placement of the required thermocouples as needed. The instructions must be imparted in the form of binding drawings, called Wrapping Specifications Sheets, and the correct realization must be confirmed by the signature of the appointed inspector. Connecting all the required thermocouples, duly identified, to a temperature recorder, permits the realization of a chart demonstrating the correct implementation of the strict thermal treatment instructions. For managing the progress of complex projects, Quality Assurance managers may set up a central monitoring center, acquiring in real time the data streaming from all the field locations, with the purpose of detecting discrepancies as they happen, to allow immediate intervention for correcting faulty processes. Interested Readers involved in welding and heat treating the above mentioned steels, or with general curiosity, can profit by seeking the original article, to read on recent improvements and innovations related to this subject.
8 - Site Updating: Cold Spray, Resistance Brazing The Pages of this Month added recently to the website, include an introduction to Cold Spray, and an explanation of the particular characteristics of Resistance Brazing, a brazing process using heating from current passing through the electrodes and the joint. Cold Spray is a coating process that, although derived from Thermal Spray processes, avoids the use of heat sources, using instead compressed gas delivered through a Venturi nozzle, to propel fine particles of selected substances to supersonic speeds on the prepared substrate. Amazing coating results showing elevated adherence, high hardness and almost complete absence of internal defects are exactly what one needs for delicate applications where the surrounding area must be prevented to heat up lest it is damaged. Accumulating experience demonstrates that in many industries the cold spray coating is the most suitable for solving specific problems. New applications are constantly developed. See the new page on Cold Spray. The second page, on Resistance Brazing, describes a brazing process using heating developed in the joint by the electric current passing through the electrodes under applied pressure. The capability to generate heat only where it is needed has many advantages that should be explored for suitable applications. Click on Resistance Brazing to see this new page. You can keep updated by subscribing to the RSS (follow instructions under the NavBar in each page), by looking at the Site Map, or by reviewing periodically the Welding Blog. Let us have your comments, feedback or questions by using the form available at Contact Us.
9 - Short Items 9.1 - Contaminant is any impurity or foreign substance present on the surface of a material or in the environment, that disturbs the successful performance of a process. 9.2 - Melting Range is the range of temperatures over which an alloy, that does not display a definite melting point, changes from solid to liquid upon heating. On a phase diagram it appears as the range of temperatures from solidus to liquidus at any given composition . 9.3 - Metallic Glass is the product of specific technologies like super fast cooling that inhibit the normal crystal formation and provide disordered microstructures at room temperature. 9.3 - Protective Atmosphere is an artificial environment or vacuum provided in a suitable container or furnace, designed to remove all types of contaminants likely to affect any process. 9.4 - Recrystallization is the formation of a new, strain-free grain structure from that existing in cold-worked metal, usually accomplished by heating. The change from one crystal structure to another, occurs on heating or cooling through a critical temperature in the solid state. Also a process by which one crystal species is grown at the expense of another or others of the same substance but smaller in size. 9.5 - Sieve Analysis is a method of determining particle size distribution, usually expressed as the weight percentage retained upon each of a series of standard screens of decreasing mesh size.
10 - Explorations: beyond the Welder Mark Roth: Suspended animation is within our grasp (Video) A genome story: 10th anniversary commentary by Francis Collins Harnessing the world’s collective intelligence to deal with climate change Natural Gas Could Serve as 'Bridge' Fuel to Low-Carbon Future Michelangelo's secret message in the Sistine
Chapel: A juxtaposition of God and the human brain
11 - Contribution: Straightening a Pipe Distorted by Welding By John P. Stewart Steel pipes as a rule are reasonably straight, but when exposed to welding, they can distort to an excessive degree, unless preventative measures are exercised. See fig. 1.
Example showing how welding a series of plates to a pipe will result in a severe bow if precautions are not taken Make a secure set-up for straightening a distorted pipe Valuable time can be lost if an attempt is made to flame straighten a bent pipe of this nature by applying a few hot shots on a trial basis. This is the wrong approach and will compound the degree of bend rather than eliminate it. The pipe must be fastened in both a flat and lateral position. [Fig 2 shows how to proceed.] Since the welding is responsible for the bend, apply the heat to the surface diametrically opposite to the weld. The wall thickness of pipes is generally quite thin, so the width of the hot shot must be minimal. The length should be similar to the length of the weld and of course a light cherry red temperature [about 538 0C = 1000 0F]. When the work cools off and the fasteners have been removed, the pipe should remain straight. Refer to fig. 2 for the step by step work process sheet. Work Process Sheet for straightening a distorted pipe. SUBJECT: Pipe distorted caused by welding plates MATERIAL: 3" Steel Pipe, 1/4" Wall Thickness REMARKS: Welding a series of steel plates has caused a severe bow to steel pipe. Use the following instructions to salvage. WORKING PROCEDURE: 1. Do not attempt to flame straighten without a secure set up. 2. Make set-up whereby pipe can be clamped or dogged down flat, and wedged against stoppers. 3. Force pipe into straight and flat position using clamps or dogs. 4. Apply hot shots directly opposite to welds as shown in sketch below. Use tip #50 or approximate. Hot shots should be same length as welds. 5. Wall thickness of pipe is 1/4 in. Keep hot shot width minimal. 6. Fast cool, using air or water. 7. Remove clamps or dogs.
For information on other topics visit Note: - I am grateful to John who made this contribution available to our readers. Other authors ready to send their contributions for publication will be welcome.
12 - Testimonials On Mon May 24 21:51:12 2010, the following results were submitted from the "Form 5" on welding-advisers.com: Name: Richard Nordin Date: 25 May 2010, 09:45:31 PM Thank You.
On Wed Jun 02 09:38:38 2010, the following results were submitted from the "Form 5" on welding-advisers.com: Name: Paul
Ipolito
13 - Correspondence: a few Comments 13.1 - At least two correspondents, interested by the oil spill, asked about welding repair. Forget it. Unfortunately the technology for welding at that depth (1500 m ~ 5000 ft) under the ocean is, at the present time, simply not
available. See: 13.2 - A hopeful correspondent asked the following question: 13.3 - But surprises come also from more sophisticated correspondents, like this Materials Engineer(?!) who wrote: I doubt anyone could give a meaningful answer, with such an incomplete description of the detailed spot weld design, and without knowing how and how much the dowel pin will be stressed. If someone understood the question I will be grateful for an explanation.
14 - Bulletin Board 14.1 - Trends in Welding
Conference 14.2 - The World of Energy Conference – Welding's Greatest Challenge 14.3 - FABTECH 14.4 - The 30-Second Nutshell Version of CTPM http://ctpm.sitesell.com/Quark.html
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keywords: Chromium Steels, Creep Strength Enhanced Steels, Weld Design, Power Generation, Bulletin 51 PWL#083B - Resources on Creep Strength- Enhanced Steels, Code Changes for P91/T91, 9–12% Chromium Steels, Weld, Repair & Heat Treat, Advances in materials and technology, Performance, Monitoring, Residual Life, Fossil Power Plants and more...
Important AnnouncementFor assembling at no cost your own Encyclopedia Online, Get Both Now at 20% Discount!Please be advised that the above Discount will be soon discontinued. Enjoy it now while it lasts! Introduction The Mid Month Bulletin is now integral with and appended to the regular PWL publication. The subject of this Bulletin is quite hot for anyone concerned with Fossil Power Plants, design, installation, monitoring , maintaining and repairing. But it could have a wide interest for general readers that may be amazed to learn that minor microstructural changes in the Heat Affected Zone of welds in these advanced materials, could have catastrophic and expensive consequences. You can bookmark this page or save it in a suitable folder with a meaningful title in your computer for future reference. General Information Growing experience with P91/T91 forcing essential code changes (10 pages) 9–12% Chromium Steels: Part One P91 and Beyond (5 pages) Guideline for Welding Creep Strength-Enhanced Ferritic Alloys (68 pages) X20 CrMoV12-1 Steel Handbook (70 pages) Fossil Materials and Repair - Program 87 - Program Overview (9 pages) Welding of ferritic creep-resistant steels Advances in welded creep resistant 9-12%Cr steels Component Integrity Solutions The role of advanced materials and performance-driven design criteria
(Presentation - 38 slides) Design of Creep–Resistant Steel Welds Creep Resistant Alloys - Reference Articles from the University of Cambridge Design of Ferritic Creep-resistant Steels (18 pages) Welding and Postweld Heat Treatment of P91 Steels Grade 91 and Other Creep Strength Enhanced Ferritic Steels Metallurgical Research Welding of Martensitic Creep-Resistant Steels Recent Advances in Creep Resistant Steels for Power Plant Applications Contributions of different factors to the improvement of the creep rupture strength
of creep resistant martensitic steels (6 pages) Lecture 8: Creep–Resistant Steel, Case Study (19 pages) Creep Resistant Ferritic Steels for Power Plants (24 pages) Alloy Design of Nano-
sized Precipitates Bearing High-strength Ferritic Heat-resistant Steels Improving the Performance of Creep-Strength-Enhanced Ferritic Steels (7 pages) Improving the Performance of Creep-Strength-Enhanced Ferritic Steels (presentation 17 frames) Development of High (7–12%) Chromium Martensitic Steels (23 pages) Characterisation of Microstructure in 9 % Chromium Ferritic Steels using Ultrasonic
Measurements (15 pages) Links to the Mid Month Bulletin Pages are listed in the regularly updated page on Welding Resources (Opens a new Window). We urge our readers to Bookmark this page or to subscribe to our Welding Site Blog by clicking on the orange buttons under the NavBar in each Website page.(www.welding-advisers.com)
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