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.
Click on Contact Us (opens new page).
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.
Click on Subscription (opens new page).
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
This 84th issue of Practical Welding Letter falls probably in a bad moment. Most of our readers are busy longing for their long deserved vacation and may have little patience for exotic welding topics.
Anyhow this issue starts with a presentation of Numerical Welding Simulations. To overcome uneasiness and distress that this subject may cause in sensitive readers, one should only know that fancy procedures exist meant to give answers to practical problems, especially those of welding generated distortions.
In case of need, asking the experts to run for you a simulation may be a smart move, especially if it can spare useless trials, time and expenses. To get an idea of the subjects researched by these theoretical exercises, one can see the titles of some research papers reported as a resource in our Mid Month Bulletin, by now published at the end of this regular issue.
Then we recommend not to dismiss arc strikes as unimportant blemishes, because they affect part integrity and may become a danger if left in place without a thought.
It may be interesting to know that the development of new and improved filler metals may take long years and cost untold efforts of the best scientists. The referred articles shed some light on the complexity of the issues dealt with, and give some perspective on the need and urgency to solve the problems encountered in building advanced fossil burning power generating facilities.
Shot peening is well known as the miracle solution for fatigue prone items, especially in aerospace applications. It may be less known however that fatigue loading may cause partial relaxation of the induced compressive residual stresses, leaving the parts less protected, unless suitable monitoring and control is carried out.
In section 8 further down one can find the new pages added to the website this month. They are about welding Fume Hazards, that must be under control to protect welders' health, and about Creep Testing, that provide essential data for the correct designing of structures for service at elevated temperatures.
Then a short note with some explanations is dedicated to those welders who may think that pursuing a new career as a Certified Welding Inspector might be worthwhile and rewarding for them. As it involves wide knowledge and high responsibility, this specialized profession enjoys status recognition and provides valuable advantages that should be considered.
The rest of the departments can be found at their usual place. Readers are reminded that the Mid August Bulletin is now appended at the end of this regular issue. This time it provides resources on papers dealing with numerical welding simulations, to give an idea of the problems treated by numerical methods.
If you are just curious to explore past issues of this publication, you can find a clickable Index of Past Issues of PWL.
As everybody else, I will take a few days off, therefore the answers to your question may suffer a certain delay. I will answer when I come back. Pleasant vacation time to all, see you later.
2 - Article - Numerical Welding Simulations
In a previous issue of this publication (Issue No. 79 for March 2010) Prof. Y. Adonyi introduced the principles of physical simulations of welding by using Gleeble equipment, capable of imparting onto suitable specimens the physical conditions (essentially heating and cooling cycles under load) realized in welding processes, for the purpose of generating specific microstructures and for examining their behavior in practical applications.
There is another way, completely theoretical, to generate on a computer the simulation of a real process for learning practical hints and information. Both ways are used, to cover different questions.
In this article the principles of numerical simulation used to represent quantitatively the evolution of physical systems are briefly presented. For simple processes perfectly described by a physical law, the practical outcome of the calculation is expressed by the solution of a well known formula.
As an example consider an unconstrained body, of a material whose coefficient of thermal expansion (CTE) is known from experimental determination, whose geometric dimensions are measured at room temperature. To calculate the volumetric expansion, after it is subjected to heating to a different given temperature, the dimensions at that temperature are calculated by solving the applicable formula.
Unfortunately the analytical solution of complex physical processes like welding becomes quickly unmanageable even for relatively simple systems due to the reciprocal influences of the different factors involved.
However, the study of physical phenomena by numerical simulation, if possible, would have many advantages when compared with testing of complete constructions. In particular, finding by mathematical manipulation on a computer unacceptable consequences deriving from a certain set of parameters, would permit to test if a more acceptable outcome could be caused by a different set.
Among the practically important results that can be obtained by applying numerical methods, distortion can be predicted with remarkable accuracy. Residual stresses and microstructure predictions are less accurate but still useful. Also of indicative value is the prediction of conditions likely to cause the formation of specific kinds of weld defects, although not the actual forecast of defect formation.
The final and most ambitious program would be to develop methods capable of estimating the mechanical properties of welds performed only on the computer. This goal is not yet available at present.
It is obvious that this kind of theoretical experimentation, if demonstrated credible in tested cases, allows important savings in time and money outlay. For this reason many centers of knowledge are operating all over the world to promote the development of suitable ways to tackle more and more complex tasks and to demonstrate the practical suitability of the results obtained.
The common way of trying to obtain meaningful answers to practical welding problems by mathematical procedures, involves the use of numerical simulations using finite elements methods. Generally this kind of analysis is performed by dividing, on the computer, the physical body under study in a large number of simple elements of definite geometry, enmeshed together as independent units to describe the total body. Moreover the composition of base and filler metal is known.
It is assumed that the welding process to be used is specified and that the distribution of input energy, the welding path and speed are given, possibly with additional factors that describe the physical changes affecting the elements involved.
The behavior of single elements as a consequence of the imposed conditions (like input energy) and the consequences on the surrounding elements are expressed in mathematical forms by algorithms that describe the evolution of the physical processes (like heat flow) following the laws of physics.
The calculations are performed once for all the elements at a given instant and define the state of each of them at that time. Special software is used to perform the mathematical operations for any single run.
Then the new state of each element is taken as the starting point for a new run, that will take into account the amount of energy added in the next time interval, together with the natural heat diffusion in the whole body object of the investigation.
The calculation process is repeated in a number of iterations, each one representing the snapshot of the conditions at a given time. By repeating the calculation runs for sufficiently frequent time intervals during a long enough period, one gets a graphic representation of the variables of interest.
One of the most used schematic pictures of this type of mathematical work permits to trace the contours of significant temperatures surrounding the place representing the weld pool, not only on the surface but also along given sections across the thickness. For conveying a more visual effect the temperature distribution can be shown according to a color scale.
While this kind of mathematical exercises are generally beyond the capability of the average welding engineer, it may be important to know that theoretical predictions can be given by experts in the field. It may be advantageous to profit from these modern tools in cases of complex projects where traditional experience cannot give reliable indications on the suitability of available processes.
As an illustration to the kind of problems studied and of proposed solutions, a number of published research papers are reported in the special Mid August Bulletin presented at the end of this issue.
3 - How to do it well: Disposing of Arc Strikes
Arc Strike is a surface discontinuity caused by a localized application of an electric arc. It appears as remelted or heat affected material or as a surface change. During welding it may be caused by arc initiation not exactly where the weld puddle is formed.
Depending on the material and the application, the blemishes appearing on the spot need to be cleaned and removed because they include remelt material, hard spots and possibly cracks. In case of low carbon steel it will be enough to grind out the surface lightly to remove the apparent discontinuity.
For medium or high carbon steel, removal of the heat affected zone is required by grinding to some depth, to be sure that no spots with untempered martensite will remain near the affected surface.
An interesting point was clarified by Damian J. Kotecki in his Stainless Q&A note published at page 14 in the July 2010 issue of the Welding Journal. There the reference is to the Duplex Stainless Steel type 2205 which is not hardenable.
Answering to a concerned reader who was annoyed by the insistence of an inspector who requested the removal of the complete heat affected zone, Mr. Kotecki justified the inspector's request explaining that in the said material arc strikes generate locally almost 100% ferrite in the HAZ.
By a complex chain of events, the nitrogen (austenite former) which has no time to reach the austenite and diffuse there, precipitates as chromium nitrides in the large ferrite grains. Therefore the ferrite grains remain depleted of chrome and prone to corrosion.
Interested readers are urged to see the original note. In conclusion arc strikes should be avoided but, if present, they should be thoroughly removed.
4 - Improved Filler Metals for High Temperature Dissimilar Metal Welds
The EPRI (Electric Power Research Institute) developed an improved New Nickel Filler Metal called P87 for Dissimilar Metal Welds and Repair, intended for use in power plants.
A short report describing the need to improve the performance of dissimilar welds between low alloy steels (the low temperature side of power plants) and stainless or high nickel components (used for higher temperature side) indicated two of the main problems of the then current filler metals.
One was the difference in the rate of thermal expansion among alloys and filler metal. The other was the creation of a weak carbon denuded zone next to the fusion line, due to carbon migration from the low alloy base metal to the high-alloy filler metal.
To improve on these difficulties, EPRI developed a lower chromium filler metal called HFS6, that was intended to solve these problems. However another problem surfaced consisting in microfissuring tendencies.
See the article:
Improved Filler Metal Enables Higher-Temperature Dissimilar Metal Welds
A detailed discussion of the approach for solving the microfissuring problem is presented in the following document.
Development of a New Nickel Filler for Dissimilar Metal Welds and Repair (238 pages)
5 - Online Press: recent Welding related Articles
Connect - May-June 2010
Shifting to Pulsed MIG Process Lowers Total Welding Costs (3 pages)
Welding and Coating Metallurgy (downloadable from:)
Accelerating business with EB welding
6 - Terms and Definitions Reminder
High Power Density Processes are Electron Beam, and Laser Beam Welding, whose concentrated power density is way higher than that of any other welding process and permits deep penetration with the keyhole method.
Inspection includes the overall quality control and assurance activity that consists of examination, testing and evaluation.
Liquid Penetrant Examination permits to detect indications open to the surface in nonmagnetic metals, using tightly controlled standard procedures and certified inspectors.
Monitoring of weld parameters is done using suitable measuring instruments. Control of manual welding process is performed by the skilled welder through coordinated actions.
Preparation is the planned set of operation of cutting to dimensions, edge machining and cleaning, needed to arrange the members of a joint for proper fit-up before welding.
Safe Practices are the complex of rules, regulations and provisions issued by appointed authorities to protect welders and workers in general from the dangers specific of welding and cutting activities. The ANSI Standard 49.1 - Safety in Welding, Cutting and Allied Processes should be always enforced.
Tubular Connection or joint (other than end to end) is done between two or more members, at least one of which is tubular. Such Connections are characterized by high strength and greater rigidity if compared to standard structural shapes.
Ventilation is the natural or forced movement of clean air in the vicinity of weld produced fumes, to control and reduce the concentration of dangerous particles. It is considered adequate when fumes and gases are kept out of breathing zones and working space.
Weld Metal, one of the three constituents of a weld (together with base metal and heat affected zone) is characterized and differentiated by its as-solidified structure.
7 - Article - Relaxation of Shot Peen Induced Residual Stresses
It is known that cyclic or periodic application of variable loads upon mechanical structures promotes the nucleation and growth of cracks, describing the failure mode called fatigue. That is true even if the stresses generated are well below the yield strength of the materials in cause.
One of the known and most applied processes intended to improve the resistance of mechanical structures
to fatigue consists in inducing the formation of residual compression stresses into the surface layers of the parts involved, by means of shot peening.
This is well known and accepted. It is also known that the beneficial prestresses can be annealed and relaxed at higher temperatures. What is probably less known is that the same processes of cyclic stress and strain application cause, in time, partial relaxation of the original residual stresses.
The consequences, studied in many research papers, point to the conclusion that shot peening is only a partial and temporary solution, and that its efficacy is due to be reduced in time, with the progression of stress relaxation by fatigue cycles. This ascertainment implies that the remaining useful life of critical shot peened components should be assessed periodically.
Another consequence of the non uniform stress relaxation may be the appearance of deformations.
The Compressive Residual Stress Fields resulting by shot peening depends on various parameters. In the industrial practice the shot, that is the type of the impinging bodies, is described by accepted standards (such as SAE J444) as to its material, hardness, shape and size and percentage size distribution (by weighing the percentage passing through a defined progression of sieves or screens).
The process itself is defined by the parameters of impingement, (angle, nozzle distance, shot velocity, coverage). It is controlled using Almen strips, metal strips undergoing shot peening as the parts, and then used for measuring their bending arc as a visual proof of the intensity of the blast stream and of the compressive stresses introduced on the strip surface.
In the papers reviewed for this note it was concluded that the initial residual stress did not remain stable during the component’s fatigue life. Also that the stress relaxation is directly related to the applied stress and to the number of fatigue cycles to which the specimens were subjected.
Instead of using x-ray diffraction to assess the remaining level of residual stresses, it might be possible to reckon the progressive relaxation by fatigue loading shot peened Almen strips, measuring after each successive run the decrease in the height of the arc. Complete relaxation would leave the strip flat.
On this subject see the website page on Shot Peening.
8 - Site Updating: Fume Hazards, Creep Test
The Pages of this Month, added recently to the website, cover two unrelated subjects.
Fume Hazards concern the dangerous conditions affecting all welders likely to breathe the fumes developed while welding. Due to their harmful consequences on human health, management and welders alike should be alert on the dangers and on the essential protective measures to be implemented.
Welders have the largest part of responsibility in caring for their own health. A sloppy welding environment should not be tolerated even in those parts known as third world.
Welders should know that little recognition of responsibility from the part of the employer or of Courts can be expected once the welder's health is severely compromised.
The time to act is while welding. If working condition are unsafe, the maximum effort must be done to improve them until they are no more dangerous.
Find this page by clicking on Fume Hazards.
Creep Test permits to determine experimentally the amount of deformation as a function of time for different materials under constant tensile forces and elevated temperature. The minimum creep rate is the design value used, with other criteria, to plan failure resistant structures operating at elevated service temperatures.
See Creep Test.
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.
Inform your friends of this website: they may benefit from the quite extensive information available.
9 - Short Items
9.1 - Hob is a rotary cutting tool with its teeth arranged along a helical thread. It is used for generating gear teeth or other evenly spaced forms on the periphery of a cylindrical workpiece. The hob and the workpiece are rotated in timed relationship to each other while the hob is fed along a definite direction (axially or tangentially) across or radially into the workpiece.
9.2 - Intergranular Fracture (or intercrystalline) is a brittle fracture of a polycrystalline material in which the fracture occurs between the grains, or crystals, that form the material. Typical of high temperature failures, as seen in Stress Rupture specimens.
9.3 - Light Metal is one of the low-density metals, such as lithium, aluminum, magnesium, titanium, beryllium, or their alloys.
9.4 - Noble Metal is a metal whose potential is highly positive relative to the hydrogen electrode. Also with marked resistance to chemical reaction, particularly to oxidation and to solution by inorganic acids. Typical Noble Metals are Gold and Platinum.
9.5 - Press in metalworking (stamping or forging), is a machine tool having a stationary bed and a reciprocating slide or ram, operated mechanically or hydraulically, at right angles to the bed surface, the slide being guided in the frame of the machine.
9.6 - Recovery is the time-dependent portion of the decrease in strain following unloading of a specimen at constant temperature. It is also the reduction or removal of work-hardening effects in metals without motion of large-angle grain boundaries.
10 - Explorations: beyond the Welder
When the Sea Saved Humanity
An Extra Quiet Sun
Arctic Voyage Illuminating Ocean Optics
First-of-its-Kind Map Depicts Global Forest Heights
Oil Disaster: A Race Against Time: Environmental
11 - Contributions: How to become an AWS Certified Welding Inspector
One of the most important contributions to the success of Welding as an art and a manufacturing process is undoubtedly given by those professionals who train themselves to perform the duties of Welding Inspector.
For an ambitious welder who already masters the required skills and who knows a good weld when he/she sees one, undertaking the welding inspector career may be an interesting and rewarding avenue. It is true that there are minimum education requirements, but this should not be an obstacle.
For one thing, dedicating hours of study to acquire the needed qualifications is in itself mind opening and gratifying for interested individuals. Furthermore by passing the examination requirements one reaches the most coveted Certification that opens doors to a less physically demanding job and possibly to a better pay.
As long as welding is needed there will always be a good place for competent and conscientious Certified Welding Inspectors.
Readers are referred to the AWS page
The above page introduces the inspector's job as engaging and promising, and details the requirements, providing data and ways for achieving the goal.
It then explains code requirements and how to learn them for the examinations in the AWS prepared, time effective intensive seminars and preparatory courses.
A detailed time table is presented to show when and how the learning material is taught.
One of the best advantages could be the Visual Inspection Workshop, providing candidates with the knowledge and the experience to make logic decisions to meet requirements by accepting or rejecting discontinuities.
From the above page one can download the complete package with application forms, education required, and a short list of the Body of Knowledge needed to pass the examination.
It is also explained that Certification is not a dead end. It offers further branching to other related careers in non destructive inspection and more diversified jobs.
Readers who think that pursuing a career in Welding Inspection might be interesting for them are urged to explore this path more thoroughly, until they can make the informed decision that might trace their successful career for years to come.
12 - Testimonials
Date: 01 Jul 2010, 03:01:42 AM
Name: Chieu Cuxuan
E-mail Address: removed for security
Introduce Your Organization: student
Describe Your Responsibility: expert of welding
[...] Thanks a lot!
Date: 02 Jul 2010, 10:10:49 AM
Name: Carla Ellerbe
E-mail Address: removed for security
Country: United States
Introduce Your Organization: Temperature Measurement Systems
Describe Your Responsibility: Purchasing
Questions and Feedback :
[...] Thank you.
13 - Correspondence: a few Comments
13.1 - It is not surprising that students ask incomplete and confuse questions about their final project. It is exactly for clarifying their own questions that they study. I would expect more support from the teaching team, at least as to the direction of where they can find help. That is what I try to do, if possible, addressing the students to textbooks and other sources.
13.2 - What surprises me much more are confused questions from top management. They should know that no meaningful answers come from unclear questions. What surprises me even more is that, when I ask clarifying questions, I often get no answers. I hope they found what they looked for.
13.3 - Another source of baffling impression is the request for the root cause of a failure briefly and incompletely described. It seems that the inquirer asks only for a confirmation of his/her hunch, without real interest for the underlaying causes, especially if they reveal unsound practices of weld management. I would like to help, but not all questions can be answered meaningfully without knowing more about the case.
14 - Bulletin Board
14.1 - GAWDA, Gases and Welding Distributors Association,
October 3-6, Maui, Hawaii
14.2 - Materials Science & Technology 2010
October 17-21, Houston, Texas
14.3 - 36th International Symposium for Testing and Failure Analysis
November 14-18, 2010, InterContinental Hotel, Dallas, Texas USA
14.4 - Don't miss the SBI! 2.0 Home Page (buildit)
Click on the following image to watch the SBI! TV Show!
Click on this Logo NOW!
No better way to get to know SiteSell,
the Company that helps everybody build
a Business on the Internet, than following them at
Specific questions about SiteSell?
Ask the Experts. Go to:
Please continue to browse down hereafter for the Mid August Bulletin.
Copyright (©) 2010, by Elia E. Levi and
All Rights Reserved
* * *
Bulletin 52 - PWL#084B
Keywords: Welding Numerical Simulations, finite elements, residual stresses, deformations, heat distribution
PWL#084B - Resources on Welding Numerical Simulations, Finite Elements Analysis Technique, Residual Stresses, Induced Deformations, Heat Distribution, Friction Welding Simulation, Modeling of Hardfacing, Tracing the Contours of significant temperatures, and more...
August 2010 - Resources on Welding Numerical Simulations - Bulletin 52
Mid August Bulletin
For assembling at no cost your own Encyclopedia Online,
a rich collection of valuable information from expert Internet Sources, on
Materials, Volume 1,
and Metals Welding, Volume 2.
Still for a Short Time Only
Get Both Now at 20% Discount!
Please be advised that the above Discount will be soon discontinued.
Enjoy it now while it lasts!
The Mid Month Bulletin is now integral with and appended to the regular PWL publication.
The subject of this Bulletin is a collection of examples of research papers on Welding Numerical Simulations, following the article above (section 2) in this PWL#084.
It should help you for further inquiring the feasibility of a Numerical Simulation study you may consider for obtaining practical answers to the problems of your project.
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)
You may also click periodically on the Welding Blog button in the NavBar.
Previous Issues of Practical Welding Letter are available at the Index of Past Issues of PWL, while the Titles of important Articles published there are in the page on Welding Topics.
The addresses reported hereafter were live and correct at the time of their publication. There is no guarantee that they will always be so, because they are administered by the sources themselves and are under their control.
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.
If the information is important to you as we hope, you may save the selected pages in a suitable folder on your Computer for easy reference. You are welcome to forward this page to those of your friends who may profit of this information.
* * *
Numerical Simulation of Resistance Spot Welding Process using FEA Technique (12 pages)
Numerical simulation of the welding process (SNS)
Numerical simulation techniques
Numerical Simulation of the Friction Stir Welding Process
(Abstract - Full text available)
Numerical simulation of transient temperature and residual stresses
in friction stir welding of 304L stainless steel (10 pages)
Simulation and Modeling of Residual Stresses due to Overlay Welding
Application of a Front Tracking Method in Gas Metal Arc Welding (GMAW) Simulation (33 pages)
Numerical Simulation of Pulsed TIG Welding Partial and Full Penetration
Finite Element Simulation of the Process of Aluminum Alloy Resistance Spot Welding (9 pages)
Large-scale finite element analysis of arc-welding processes (7 pages)
Automatic Weld Planning by Finite Element
Simulation and Iterative Learning (10 pages)
Simulation of Weld Pool Dynamics (13 pages)
Numerical modelling of FSW processes
Numerical Simulation and Experimental Study for Magnetic Pulse Welding
Plasma Arc Welding Simulation with OpenFOAM (85 pages)
Modelling the transient behaviours of a fully penetrated GTAW pool
Modeling of Friction Stir Welding (FSW) Process with Smooth Particle Hydrodynamics (SPH)
Finite Element Analysis of Residual Stress in Butt Welding Two Similar Plates (4 pages)
Simulation of distortion induced in assemblies by spot welding (11 pages)
Improved weld seam quality using 3D FEM simulation in correlation with practice (13 pages)
Numerical and experimental investigation of Laser Beam Welding of AISI 304 Stainless Steel Sheet (13 pages)
Finite Element Modelling and Simulation Of Welding of Aerospace Components (50 pages)* * *
Happy Vacations to All!
If you think that this page might be useful, you are invited to forward it to a Friend.
If you received this page from a friend, please note that you can get at no cost every new issue of Practical Welding Letter, by clicking on Subscription
(Opens a new Page).
You will also receive a bonus book on
"Practical HARDNESS TESTING made simple".
If you want to contribute from your thoughts and experience visit our new page reachable by clicking on Welding Talk and typing or copying directly in the form.
Your comments are welcome.
Click on the following image to watch the SBI! TV Show!
Click on this Logo NOW!
Copyright (©) 2010, by Elia E. Levi and
All Rights Reserved
See you next time...