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PWL#062 - Acoustic Emission, Hinge Design,Nickel Filler Metal, Brazing Defects, AWS D1.1 changes October 01, 2008 |
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| We hope you will find this Letter interesting and useful. Let us know what you think of it. PWL#062 - Acoustic Emission Inspection of Weldments, Designing a Hinge, Filler Metal for Nickel Welding, Brazing Defects, Ultrasonic Welding, Welding Nickel, Changes in AWS D1.1 and more... DON'T USE REPLY to send us your messages! Use Contact Us instead. 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 selected them 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 2 - Article - Acoustic Emission Inspection of Weldments 3 - How to do it well: Designing a Hinge 4 - Filler Metals for Welding Nickel: 5 - Online Press: recent Welding related Articles 6 - Terms and Definitions Reminder 7 - Article - Brazing Defects 8 - Site Updating: Ultrasonic Welding, Welding Nickel 9 - Short Items 10 - Explorations: beyond the Welder 11 - Contributions: Changes in AWS D1.1 12 - Testimonials 13 - Correspondence: a few Comments 14 - Bulletin Board
1 - Introduction Hello from the 62nd Issue of Practical Welding Letter. It would be nice to get some feedback: let us know which subjects are more interesting to you. We recall a known nondestructive testing method (Acoustic Emission) that is quite useful in definite situations. Maybe some of our readers will be spurted to explore if applying these methods to their situation can help them in reaching goals in monitoring weldments behavior. A reader asked for help in designing a certain implement. Perhaps other readers too will be interested in knowing how to test a design involving moving parts. We would like to hear that the problem was solved satisfactorily, but unfortunately we did not hear that yet. Then we provide some additional information in the Section on Filler Metals, with reference to our new website page on Welding Nickel that includes two Tables giving nominal composition of selected nickel filler metals. The next article describes a few of the common brazing defects, following some queries we were made aware of. For the Site Update we introduce the two new pages, one on Welding Nickel as mentioned above, the other on Ultrasonic Welding, a very useful cold process for certain specific applications. We report further down the page on a recent article that explains the changes introduced to one of the most important specifications on welding steel. The short exposition may induce interested readers to look for the original article and to study the modified Code itself. Then we have the other usual departments where you may find additional information. We welcome your feedback. Click on Contact Us. 2 - Article - Acoustic Emission Inspection of Weldments A short presentation of this subject was published (9.1) in Issue no. 12 of Practical Welding Letter for August 2004. Here these arguments are elaborated somewhat on the uses of Acoustic Emission for Welding Inspection. Acoustic Emission is a very versatile and useful, non-invasive method for collecting information on materials or structures. Acoustic Emissions (AEs) are transient elastic waves from a source within a material. They are due to localized rapid release of energy produced by the sudden internal stress redistribution caused by changes and small displacements in the internal structure. Changes likely to produce Acoustic Emission events are crack initiation and growth, crack opening and closure, plastic deformation, dislocation movement, twinning, and phase transformation in monolithic materials. In composites, Acoustic Emission events are due to fiber breakage and fiber-matrix debonding. Most of the sources of Acoustic Emissions are damage related. Therefore the detection and monitoring of these emissions are commonly used to predict and prevent material failure. Acoustic Emission tools are ultrasonic transducers (usually piezoelectric) that are attached to the material to passively detect Acoustic Emission waves. Most of these sensors are in the frequency range of 20 kHz to 650 kHz. An acoustic emission sensor in contact with the material being monitored, detects the mechanical shock wave and converts the very low displacement, high frequency mechanical wave, into an electronic signal that is amplified by a preamplifier and processed by the Acoustic Emission instrumentation. Used as a monitoring technique, Acoustic Emission detects the sound energy from emitting sites well away from sensor locations. An array of sensors is capable of detecting and locating a variety of emitting sources on complex structures. Acoustic Emission Monitoring Acoustic Emission has been widely used in industries, including for the detection of faults or leakage in pressure vessels, tanks, and piping systems and to monitor welding and corrosion progress. Weld Monitoring: During the welding process, temperature changes induce stresses between the weld and the base metal. In particular spot welds can be inspected in process to verify their quality. If cracking occurs it is readily detected and located by Acoustic Emission. Leak Detection: In leak detection, the instrumentation detects the Acoustic Emission signal that is generated from the turbulent or cavitational flow through a crack, valve, seal or orifice. Existing installations include monitoring of pipelines in utility and petrochemical plants, as well as leak detection in boilers, vessels, and through valves. Vessel Inspection: One of the most successful applications of Acoustic Emission is in vessel inspection for the petrochemical industry in both metal and FRP (Fiberglass Reinforced Plastic) vessels and spheres. Sensors are placed on the vessels in arrays to monitor the entire pressure boundary. The vessel is then tested by subjecting it to pressures above previous operating levels (but below the vessel pressure rating) to monitor the Acoustic Emission activity. Acoustic Emission examination of vessels is the most sensitive and cost-effective method for vessel inspection that meets standards set by ASTM and the American Society of Mechanical Engineers. Besides traditional nondestructive testing methods, monitoring helps assessing the integrity of Railroad and Highway Bridges. Joints, welds and connections are potential stress raisers or initiation points for fatigue cracks. Acoustic Emission detects fatigue cracks growth in fracture critical tensile bridge members and monitors the progress of damaging destructive processes. See also the following Standards: ISO 12713:1998 Jul-1998 ISO 12714:1999 ISO 12716:2001 Jun-2001 ASTM E1316-08a
ASTM E749-07 The following article overviews a few international Standards. Acoustic Emission Standards and Guidelines 2002 See also: Acoustic Emission: Heeding the Warning Sounds from Materials Acoustic Emission How does it work? Basics of Acoustic Emission Introduction to Acoustic Emission Testing Acoustic Emission Weld Monitor System. Standardization of Acoustic Emission Inspection for Seam Welded Hot Reheat Piping (3 pages) Using Acoustic Emission in Fatigue and Fracture Materials Research
3 - How to do it well: Designing a Hinge Q - How to design a hinge for the rear of a platform dump, if running into clearance issues with the swinging part? A - Take a clear new sheet of paper. Mark a small cross in the center. Use your compass to draw a circle representing your hinge. Draw the fixed section of your application either at 1:1 or in scale. On a separate transparent paper, draw the section of the rotating part at the same scale, starting from the circle that represents the hinge. Now take the transparent paper with the drawing of the moving part and put it on the drawing of the fixed part so that the circles of the hinge match exactly. Pierce with a pin the center of the hinge of the moving part so that it can move around the pin at the hinge center. You can now swing carefully the moving on the fixed part. Examine for eventual interferences and unwanted clearances. Modify the drawing until you are satisfied with the result, and then build it. Readers can send their problems to the Welding Advisers Website using the Contact Us form.
4 - Filler Metals for Welding Nickel The following AWS Nickel Base Filler Metal Specifications should be consulted for selecting and purchasing Nickel Base welding Filler Materials. ANSI/AWS A5.11/A5.11M:2005 ANSI/AWS A5.14/A5.14M:2005 ANSI/AWS A5.34/A5.34M-2007
Specification for Nickel-Alloy Electrodes for Flux Cored ArcWelding Two Tables of selected designations and approximate nominal compositions of Filler Metal Electrodes and bare Wire are published in our recent Website page on Welding Nickel that can be found online. For exact limits and requirements refer to the official AWS documents.
For welding Nickel 200 and Nickel 201, use Filler Metals ENi-1 or ERNi-1. For Alloy 600 and 601 use ENiCrFe-1, ENiCrFe-3, ERNiCr-3 Alloy Development of Nickel-based Superalloy Weld Filler Metals
5 - Online Press: recent Welding related Articles From The Fabricator: Download Prepublication articles from ASM Handbook Vol 15 - Casting
Download Sample Chapter on Techniques of Failure Analysis from Welding Repair 6 - Terms and Definitions Reminder Flashback Arrester is a device intended to stop the back propagation of a flame in an oxy-fuel torch in the direction of the fuel supply. HVOF - High Velocity Oxygen Fuel is a special Thermal Spray process that uses a high pressure mixture of oxygen and a suitable fuel to generate a high velocity flame that heats and propels surfacing material in powder form upon a substrate. Joint Geometry represents the shape, the dimensions of the elements and their relative positions as they are prepared to receive the welding process. Metal Powder Cutting is an oxyfuel torch cutting process, whereby metal powder is injected in the flame to help burn and displace the material that is being cut. Nondestructive Examination is performed by any of a number of methods and techniques using physical principles to probe the integrity of materials or constructions and to assess their suitability for service without affecting their serviceability. Oxyfuel Gas Welding Torch is a device that permits to generate a high temperature flame by controlled burning of a fuel in presence of oxygen and by directing it onto the workpiece to perform flame welding or brazing processes. Shunt Effect (in resistance spot welding) is the deviation of part of the welding current flowing between the electrodes, through the path of previously welded spots. Welding Procedure is the detailed sequence of steps, methods and operations needed to perform a given welding job. 7 - Article - Brazing Defects This article is written as an answer to a few searches that were performed recently in this website for the terms included in the title above. During the development of brazing processes it is customary to perform destructive testing on test pieces to determine regularity and fullness of filler metal spread. It is important to study the presence of defects in given processed parts in order to look for the reason that promoted their appearance and to perform corrective actions in view of obtaining acceptable production. In presence of brazing defects, the design, the application of physical principles and the details of the brazing operation must be examined thoroughly to determine which steps in the preparation were inadequately performed. The presence of defects undermines joint integrity to the point that brazed items may fail to perform their function and may cause further damage. The Designer is responsible to establish the limits of acceptability for each type of defect. The Types of common defects are listed hereafter: Cracks formed while cooling may be due to liquation of filler metal or to shrinkage movements. Cracks are almost never allowed because of the danger of their spreading under fatigue stresses and severely limiting load carrying capacity. Noncontinuous filler coverage. In the visible part of the joint can be detected by visual inspection, and be acceptable or not depending on requirements. Lack of Fill (Voids, Porosity). May be due to improper or insufficient cleaning, large clearances, not enough filler metal, residual gas, low brazing temperature, inadequately protective or oxidizing atmosphere, lack of flux, stopoff in wrong place, inadequate fixturing permitting movement when filler metal is molten. The mechanical strength of the joint is impaired and a leak path may result. Flux Entrapment can result from spreading molten filler metal flow failing to expel the residual flux through insufficient vents. If corrosive it can attack the joint. Base metal erosion. Usually visible in metallographic sections. Consists in dissolution of base metal due to alloying of filler with base metal. It can proceed along grain boundaries as intergranular attack causing weakening of joint strength. Unsatisfactory surface appearance can consist in overflow of excessive filler metal, result in rough unacceptable surface because of notch effect or preferred corrosion starting locations and may interfere with brazing inspection. See the following article that discusses the repair aspect of brazing defects. Fixing Faulty Jobs and Worn-Out Components 8 - Site Updating: Ultrasonic Welding, Welding Nickel The first Page of this Month recently added to our Website deals with a somewhat different process, a kind of cold, solid state welding, that is enjoying increasing applications in special niches, that of spot welding for aluminum automotive structures and that of connections in the electronic industry. It is about Ultrasonic Welding, an interesting process both for manual and for mechanized or robotic applications. By studying Advantages and Limitations one can see if it is suitable to solve definite situations, satisfactorily and economically. The other page deals with Welding of Nickel, an important material useful for Corrosion Resistance, for Cryogenic applications, for Gas Turbine Engines and for Heat Resistance. Not all Nickel Base materials are equally weldable. One has to learn the differences and how they can be welded, by which processes and with which filler materials. There are multiple choices to be further refined but one should know the fundamentals, for initial orientation. Click on
Welding Nickel to reach the page. Readers are urged to use the Google Search window that appears in almost every page of our Website to locate specific information and links. Another method to find one's way in the maze of this Website is to look at the Site Map. Let us know how can we be of help. Use the Contact Us form and we will do our best.
9 - Short Items 9.1 - Hysteresis referred to magnetic processes is the lag of the magnetization of a material behind cyclic variations of the applied magnetizing field. When referred to mechanical systems where loads are repeatedly applied and withdrawn, it represents the energy of deformation absorbed or lost in the form of heat. 9.2 - Slip is the plastic deformation by shearing translation of one part of a crystal relative to another on specific crystallographic planes in definite crystallographic directions. 9.3 - Tool Steel is a loose definition of ferrous material commonly used to make tools. Tool steels display elevated hardness and resistance to abrasion, with toughness and strength even at high temperature. These qualities are promoted by suitable heat treatments on compositions including high carbon and alloy contents. 9.4 - Twins represent two parts of a crystal with definite orientation relationship. The orientation of one of the twins is a mirror image of the orientation of the other across a twinning plane. Alternatively the orientation of one twin can be derived by rotating the other around a twinning axis. 9.5 - Vacancy in the microstructure of a material is defined as a structural imperfection in which an individual atom site is temporarily unoccupied. Vacancies cannot be resolved under optical microscope but their presence is inferred by observation of material behavior. 9.6 - Whisker is a short single crystal fiber or filament that can be used as a reinforcement in a matrix. Whisker diameters range from 1 to 25 micron, with aspect ratios (length to diameter) generally between 50 and 150. Also microscopic metallic filamentary growths in certain materials (i.e. tin), formed during electrodeposition or spontaneously during storage or service. 10 - Explorations: beyond the Welder Eco-Cities: Urban Planning for the Future Nature Editorial, Creation and Classrooms Nature Podcast, Innovation Policy Nature Podcast, From the Edge of the Solar System The Large Hadron Collider (LHC) (video) 11 - Contributions: Changes in AWS D1.1 Whoever uses the AWS D1.1 - Structural Welding Code - Steel, is probably aware that a new, current 21st edition is issued in 2008. Everyone however should know of the changes and clarifications introduced. An article was published at page 32 of the September 2008 issue of the AWS Welding Journal offering a preview of the changes and an explanation for the reasons that were at their source. The article starts with a short history of origin and continuing improvements of the document content to make the Code more clear and useful. For example a requirement to make a definite transition in butt joints of unequal thickness was retained for structures subject to fatigue due to load variations. It was dropped however for static load conditions, at the request of users. The concern that increased allowable stress in fillet welds could be improperly applied, generated new provisions identifying the conditions that permit safe use of the equation, and clearly stating when the load carrying capacity should be conservatively estimated. Other requirements were added concerning the use of shielding gases for prequalified procedures, a subject that had not be covered previously. The term "temporary weld" was dropped and substituted with "construction aid weld" to better reflect the intent of the Code together with "tack weld" that was retained. Inspection requirements were revised to reflect the increased reliability of modern instrumentation, permitting to recalibrate less frequently. The limit of six month for repeating quality control of studs was dropped provided the original packaging is sealed and identified. Many Clarifications were added or moved without changing existing requirements. The article informs that most of the reasons for change and improvement are documented and can be consulted , together with the official Book of Interpretations. Suggestions are offered for dealing with those cases when a conflict of interpretations may arise recalling that best engineering judgement and accepted industrial practice can often help. Finally the author invites knowledgeable professionals to join in as volunteers to participate in future issues of the code. Interested readers are urged to seek the original article mentioned above. ANSI/AWS D1.1/D1.1M:2008 12 - Testimonials On Mon Sep 01 02:11:31 2008, the following results were submitted from the "Form 5" on Welding Advisers First Name: Verma
From: Hesaan Karim
Thanx alot for your help. Best regards, Hesaan Kareem 13 - Correspondence: a few Comments 13.1 - A baffled reader protested that he could not see the articles indicated in previous issues of this Practical Welding Letter. I apologize, I am sorry, I should have thought beforehand that possibly some of the readers do not know what to do with the indications, in order to obtain the requested pages onscreen for reading or downloading. I admit, I took for granted the unwarranted assumption that anybody knows what to do. I am going to include from now on a note to explain. 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." I prefer to give the URL's except if they are too long. These are not live and must be copied and pasted into the browser (after having selected them 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. If I copy exactly the URL and check that it works, it is no more my responsibility. That is why I prefer it. To make live links I have to transcribe URL's in a certain way, that may go wrong. In that case (as unfortunately happened to me) the responsibility is mine. I hope this should dispel the doubts. If you have difficulties, anyone with some more experience of computers can help you. When online references are given, it is essential that readers get the chance to gain access to them to enhance their learning. If the document is not available I would like to know, to correct the address if it was my fault. Occasionally the source may have removed the information previously provided, too bad.
14 - Bulletin Board 14.1 - Materials Issues in Weld Integrity 14.2 - Joining Dissimilar Metals Conference 14.3 - Can you read between the lines? Try this:
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