PWL#095 - Advancements in Pipe and Tube Welding, Avoiding Porosity in Aluminum Welding, Filler Metal for Welding Dissimilar Metals used at High Temperatures, Metallography of Welds, Comments on Complying with Welding Codes, New Weld FAQ, updated Resistance Welding Tips and much more...

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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.
Don't miss it!

However well informed and expert you may be, you could certainly benefit from a vast repository of online authoritative welding information.
The following may be just what you need...

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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.

2 - Article - Advancements in Pipe and Tube Welding

3 - How to do it well: Avoiding Porosity in Aluminum Welding

4 - Filler Metal for Welding Dissimilar Metals used at High Temperatures

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Metallography of Welds

8 - Site Updating: Weld FAQ and Resistance Welding Tips

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Comments on Complying with Welding Codes, from PWL#094

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

(Sponsored Links)

1 - Introduction

This 95th issue of Practical Welding Letter opens with a review of a few articles from the Welding Journal dedicated to Advancements in Pipe and Tube Welding. I think that people totally absorbed in their daily routine job should find the opportunity, from time to time, to refresh their knowledge and see if something interesting came up in the meantime.

Not all innovations can be applied from the shelf, but the process of thinking over exciting news may bring new ideas and possibly facilitate fruitful contacts with helpful people. Curious looking around should not be dismissed lightly, in my opinion.

Then, having seen a few queries on the matter, it became quite natural to dedicate a new article to the precautions to adopt in order to avoid porosity in aluminum welding. Welders know in principle what influences weld integrity, except that they may be tempted to try shortcuts to save time or bother. It requires self discipline to do right what one has to, but it does not pay to do otherwise.

The references to online resources, assembled in this issue for the Mid Month Bulletin, that follows the regular issue, are devoted to Avoiding Porosity and related issues as a way to deeper insight on the items discussed in the same piece.

The next article gives a few hints on the precautions one has to be attentive to, when performing welding of dissimilar metals, on structures designed to be operated at high temperatures.

Fortunately the problems are now well known, and quite clear practical instructions can be found. Nevertheless those in charge have no easy job in selecting the proper solutions to demanding applications.

Even if preparing suitable metallographic specimens is not the welders' preferred occupation, nevertheless, to advance their understanding, they should learn to interpret structural images as a study tool used to recognize the appearance of good weld sections.

Recent advances in color metallography permit to see and interpret some of the subtlest cues to what is really happening in welds, and should help in improving welding performance. Reference is given to an upcoming webinar that may interest some of the readers.

A reader kindly commented to the article on Complying with Welding Codes, that was published it the last issue, PWL#094. As he has a rich experience in dealing with Code requirements, his comments are especially to the point.

The other sections are where they should be. Your feedback is always welcome. Please don't use REPLY. Use the Contact Us form instead.

Don't miss our Mid July Bulletin #63 appended to this issue #095 of Practical Welding Letter, providing links to valuable information as Resources on Porosity Prevention.
Please see it past the end of the first part of this publication.

2 - Article - Advancements in Pipe and Tube Welding

No question that Pipe and Tube Welding covers a very important sector of global economy. Companies and shops may be quite satisfied with their own business and productivity. It may be useful however, to take a view, from time to time, of recent advancements in the art and technology of this type of welding.

This would help to remain up to date about which techniques are now available and what the current weld deposition rates could be. The productivity gains may make a difference.

In the June 2011 issue of the Welding Journals, a few articles cover exactly this topic. At page 58 an article on Welding Advances in Tube and Pipe Applications relates on recent advancements in three different welding technologies that offer the potential of increasing productivity and decreasing costs. It is based on a paper presented in November 2010 at the Fabtech convention in Atlanta.

The first review explains the advantages provided by tandem gas metal arc welding (T-GMAW), and by the narrow gap version of the same technique (NG-T-GMAW). Tandem is a variant where two electrodes are fed through a single torch. Synergistic interactions between the two arcs provide process stability and higher deposition rate.

While the advantages in flat position are known and used, new developments by the Edison Welding Institute (EWI) permit the benefits to be reached also in out of position welding. No details are given here, however. Application of the tandem technique to narrow gap configurations multiplies the benefits while assuring sidewall fusion, the biggest worry to wider usage. Details are available from EWI.

It is assumed that the capacity of pipeline systems will need to be expanded greatly, based on predictions of doubling of natural gas consumption over the next 20 years.

Then comes a promising method for successful mechanical automatic welding of new pipelines. It is indicated as the hybrid gas metal arc-laser beam welding process (GMAW-LBW) with a new prototype high power source and yet portable Yb-fiber laser (Yb = Ytterbium) and a GMAW head with pulse power supply (GMAW-P).

The project, whose details are reported in the article, sponsored by DOT (Department of Transportation), aimed to develop and apply the innovative hybrid system based on a commercially available "bug-and-band" system for mechanized welding of high strength, high integrity pipelines.

The materials of the pipes involved were X80 and X100 steels. The procedures were developed, using the equipment described, to demonstrate satisfactory mechanical properties to API 1104 requirements under field conditions.

The application requirements were successfully demonstrated for the horizontal fixed position (5G) with assured weld soundness, material properties and acceptable geometric profile.

And finally, the EWI DeepTig^TM is introduced, a collaboration of EWI with the Navy Joining Center. A patented mixture of oxide powders, available for steels, stainless steels and nickel based alloys, is applied to the surfaces to be joined. The products have already been used successfully in various demanding applications.

The advantages are listed as follows: consistent increased penetration despite heat to heat variation, simple joint and simplified preparation, less passes, reduced heat input and distortion.

The examples reported achieved substantial economy and success. A number of issues still require improvement but the process is now considered suitable for manual welding, in the past not recommended.

In conclusion, the author invites companies to explore if the purported advantages of the reviewed processes, promising increased productivity and reduced costs, are likely to interest their operations.

Another article on page 64 explains how automated features help orbital welders perform consistently high quality welds. These advantages are obtained by the synergistic influence of automatic data collection, program parameter transmission and provision of recorded documentation to external inspectors.

In process inspections minimize the chance of putting in service systems with flawed welds.

The last article in this series presents new features of a commercial development called Regulated Metal Deposition, a modified short circuit transfer GMAW technology, claiming advantages summing up to 20% reduction of weld time in industrial applications, through elimination of rework.

While the specific reported results may vary in other applications, the comments of a satisfied customer confirm the supplier's assertions.

Interested readers are urged to see the articles for themselves in the above issue.

3 - How to do it well: Avoiding Porosity in Aluminum Welding

Looking for a quick answer for resolving problems of porosity in aluminum welding may prove disappointing. Unfortunately a number of conditions relative to material, preparation, contamination, consumables, welding technique or equipment can cause porosity.

In any specific case, it is necessary to evaluate each of the possible problem areas in order to identify the culprit.

The main causes of porosity to be investigated to avoid porosity in aluminum welding are listed hereafter.

• Hydrogen gas becoming entrapped within the solidifying aluminum, from contaminants within the welding area,
• Inadequately pure gas,
• Insufficient gas shielding, as when drafts are present,
• Spatter buildup inside the gas nozzle, restricting shielding gas flow,
• Incorrect or variable nozzle distance that disturbs flow rate, coverage and efficiency,
• Inaccurate material preparation and cleaning.
• Contamination of base and filler metal, not completely removed by inadequate cleaning,
• Use of oily compressed air on the material,
• Anti-spatter compound for protecting the welding nozzle: should not be used for aluminum welding,
• Moisture presence from condensation at low temperatures or absorbed in aluminum oxide not removed.

To tackle porosity problems, the basic causes for porosity generation must be known, and adequate attention must be applied for the review of each one. No shortcuts should be attempted.

The constant application of proven procedures, with suitable equipment and consumables duly maintained and inspected, are the best means to protect against the appearance of porosity, that may become very costly to search for and to repair. Better to avoid porosity in the first place.

To provide further insight into this matter and to offer different points of view, we publish hereafter a listing of Resources on Welding Porosity in the Mid July Bulletin No. 63 appended to this issue of PWL, past the end of the regular publication. Bookmark this page.

The list provides quite a number of instructive information on the subject, readily available online. Readers can collect the files interesting them in a special folder to be saved in their computer for further reference.

4 - Filler Metal for Welding Dissimilar Metals used at High Temperatures

In this example a short discussion will consider the factors that must be taken into account when selecting suitable filler metals. The standard selection for welding austenitic stainless steel to mild or low alloy steel is shown in our FAQ page, under the title "Stainless to Mild Steel Welding".

The answer is correct if the service conditions of the application are practically at room temperature. (A note to this effect has been added there for accuracy).

It is known however that utility companies found serious problems on joints between 2-1/4Cr-1Mo low alloy steels and austenitic stainless steel combinations, used for their fossil fuel plants, when welded with Type E309 filler metal. Readers working on these materials should find interest in the conference announced at 14.2 further down this page.

The problems arise from service conditions entailing thermal excursions to elevated temperatures, that produce modifications in the steel composition. At high temperatures the affinity of carbon for chromium in the steel side, causes a region of Heat Affected Zone (HAZ) near the welds, to be deprived of carbon. This region becomes soft, less creep resistant and brittle.

Furthermore, because the austenitic stainless steels have a coefficient of thermal expansion (CTE) 30% larger than that of the low alloy steel, the repetitive thermal induced stresses at every change of heating conditions will cause thermal fatigue failures in the weaker alloy steel.

The selection of a nickel base filler metal like ENiCrFe-1 instead of the stainless type 309 is better suited to avoid those failures, albeit at a higher cost.

5 - Online Press: recent Welding related Articles

Advances in automatic orbital welding systems enhance efficiency and functionality
http://www.pacetoday.com.au/news/advances-in-automatic-orbital-welding-systems-enha

ESAB Introduces Columbus.NET(TM) Programming and Nesting Software
http://www.prweb.com/releases/2011/6/prweb8575397.htm

Alloy 52 Nickel-Base Filler Metal Weldability Solution
http://mydocs.epri.com/docs/Portfolio/PDF/2012_APC1_RD06_ALLOY-52-Weldability.pdf

Laserdyne Supplying Laser Cutting/Welding System to Aerospace Turbine OEM
http://www.americanmachinist.com/304/Issue/Article/False/87417/Issue

Highly Flexible Laser Systems Provide Efficiency
http://www.photonicsonline.com/article.mvc/Highly-Flexible-Laser-Systems-Provide-0001

6 - Terms and Definitions Reminder

Contact Tip Setback, referring to flux cored arc welding (FCAW) and gas metal arc welding (GMAW), is the distance between the contact tip and the gas nozzle end.

Direct Drive Friction Welding is a friction welding piece of equipment where a motor provides the required energy directly to one of the elements to be friction welded.

Edge Effect is the loosening of the bond between deposit and substrate, found in thermal spray at the edge of the spraying cone.

Field Weld is that performed in a location that is neither a welding shop nor the place of the original welding construction.

Gas Laser is a laser source where the element producing the lasing effect is a gas.

Heat Balance is whatever pattern of heat distribution that develops around a welding heat source as a consequence of conditions and materials present.

Induction Upset Welding is a welding method where induction heating is applied to the elements before squeezing them together for upset joining.

Joint Recognition is the automatic determination of the actual joint location by machine vision or other methods, to provide automatic correction of the welding path.

7 - Article - Metallography of Welds

Metallography is the art and science studying the structure of metals and alloys by various methods, especially by optical and electron microscopy. It is performed on suitable prepared specimens, duly ground and polished.

Of course this examination is destructive in that it is performed on sections through the location of interest. But it may be performed on separate test pieces for obtaining the information required without affecting the production structures.

Specimens may then be viewed as polished, if looking for porosity, cracks, inclusions or other features different from the metal. Then they may be viewed again, after having been etched with proper acid solutions capable of revealing the finest constituents and their size.

This occurs because of differential speed of attack, or preferential staining of the different phases, depending on their nature, their location and their orientation relative to the polished surface.

For those dealing with welds, Metallography is an essential tool for examining the outcome of application of given processes upon certain materials under well defined conditions for evaluating their suitability to meet design requirements.

The difference between macrostructural and microstructural examinations obviously reflects the size of the sought features, but also some basic characteristics. When welds are present, the former structure of base metals was drastically changed.

Macrostructural examination helps to identify the weld geometry, to find the boundaries between the base metal, the heat affected zone and the weld metal, whose solidification structure, in fusion welding, is similar to that of castings. It will show the amount of weld penetration in the base metal as well as the presence of cracks or voids and their position relative to the said boundaries.

Microstructural examination reveals the phases present in the different zones. If cracks are present, the description of their appearance and their position relative to grain boundaries may help in determining the causes and in finding ways to avoid their formation by suggesting improved welding processes.

A listing of very basic equipment for a simple laboratory is listed in my page on Welding Testing and, for a more limited purpose, in my other page on Weld Macro.

Most welding shops or departments would benefit from being helped by knowledgeable individuals capable to use the simple tools required, to obtain clear images revealing the real structure of any weldment.

Although metallography outsourcing should be always possible, in practice the time delay involved is too much for production schedules, so that some form of in house control should be preferred, if possible.

While certain Managements may object to the idea of spending money for a (perceived) non productive activity, the most open ones will welcome the requirement, if initiated from welders or their supervisors, as a way to advance the quality and the acceptability of their company to more sophisticated and demanding customers.

Depending on the practical needs, a basic laboratory can probably be set up with a modest investment and yet be able to provide in the shortest time essential answers bearing on production quality. There is no upper limit to the level of professionalism of a good laboratory technician.

But if you take a young and clever technician with basic understanding of technical issues and you appoint him/her to the new job, in a few weeks of learning and training at a suitable school or with the equipment suppliers, you will get someone capable of providing the answers you need.

Of course it will help to provide also a basic library of good textbooks on the argument and to visit other laboratories to gain insight and experience. Even those who learned the foundations many years ago and have personal hands on experience, should be aware of the amazing progress realized in recent times.

In particular for metallographic examination of weldments the use of color etching techniques with suitable digital imaging viewing, storage and reproduction, reveals macrostructural and microstructural features clearly with excellent image contrast.

It is true that good equipment is required for obtaining clarifying information, but there is no substitute for the experience and professionalism that only dedicated interest and application along a lifetime can provide.

An informative article with the same title as this note, written by such an expert, George F. Vander Voort, can be found at page 19 of the June 2011 issue of Advanced Materials and Processes, a publication of ASM International.

Interested readers are urged to Register, to join the free ASM webinar on Light Optical Microscopy presented by the same expert named above and announced further down at 14.1.

Note: - With the explosion of applications involving non metallic materials for building engineering structures, it has been proposed to enlarge to non metals the scope of the structural investigations and to call the new discipline Materialography.

8 - Site Updating: Weld FAQ and Resistance Welding Tips

The Pages of this Month are updated older pages refreshed and updated. The first is the good and old Frequently Asked Questions page, which had become too heavy and took too long time to load.

It has now been split in three pages easier to consult and navigate. The first page still lists all the questions. By clicking on any title, the answer comes into view, no matter if it is physically on the first, the second or the third page. Readers brought out of the first page should note that to see the complete list of questions again, they have first to go back to page one.

The other pages are scrollable up and down and all their answers will come into view, but again the list of questions is not there. Not a big problem, but readers should be advised to look for the list of questions where it really is, in the first page given above, before becoming too excited at the missing list...

The other page that received a substantial update, consisting in a list of short articles from Practical Welding Letters, written at different times and providing practical hints, is Resistance Welding Tips. Readers ready to share their own tips with this audience are welcome to send a short note, to be published in a future issue.

All the pages as usual are found in the Site Map and in the Index Page, but no effort is done to signal the last updates. These are generally given in the Blog page, distributed to RSS subscribers, and available directly by clicking on the button, but only if these are only one or two in any given day.

Readers are invited to Contact Us for questions, comments, feedback.

9 - Short Items

9.1 - Natural Aging is the spontaneous precipitation or aging at room temperature of a metastable supersaturated solid solution.

9.2 - Optical Microscopy is the technique used for examination of small structures by manipulating light through lenses to obtain enlarged images.

9.3 - Pyrometer is generally an optical device for measuring temperatures without contact.

9.4 - Rupture Stress or fracture stress or breaking stress designates the stress at failure.

9.5 - Swage is the operation of reducing or changing the cross-sectional area of stock to a taper shape by the fast impact of revolving dies.

9.6 - Truing is the removal of the outside layer of abrasive grains on a grinding wheel for the purpose of restoring its face.

10 - Explorations: beyond the Welder

MESSENGER's Solar Arrays Probe to Operate in Extreme Temperatures Orbiting Mercury
Space Daily.

Leap Seconds May Hit a Speed Bump
SA1.

Fukushima Meltdown Mitigation Aims to Prevent Radioactive Flood
SA2.

Book Review: The Future of Water
SA3.

Mapping the Route to Retirement
Science Careers.

11 - Contributions: Comments on Complying with Welding Codes, from PWL#094

Our faithful reader, Tony Rangus, Principal Engineer from Bechtel Oil, Gas & Chemicals sent the following Comments:

One should always determine if the state, county, borough, parish, city etc. where the pressure vessel, boiler etc. is to be erected is a "Code" state, county, borough, parish, city etc.

If the ASME B&PV Code is mandated by law / legislation, then whatever Code Section is mandated, it is required to be met or a violation of the law takes place and prosecution may occur.

The Jurisdiction may modify Code requirements as they see fit. Also, Federal authorities like FERC, DOT, DOE etc. also mandate Codes & Standards & a violation is now a Federal issue.

Most Federal authorities simply mandate by fiat, other Codes & Standards, but care must be taken when that occurs, as those Codes & Standards will also reference other Codes with their own modifications.

A very good example is the NFPA 59A Code (Std. for the Production, Storage, and Handling of LNG - Liquefied Natural Gas) which is mandated by the DOT (Department of Transportation) for plants in the United States.

NFPA 59A references many other Codes & Standards, including the ASME B&PV & the ASME B31 Codes for piping, & also modifies & changes the requirements in those Codes / Standards. Unfortunately, some Jurisdictions who try to modify Codes / Standards are woefully inadequate in welding & NDE knowledge, & thus put forth requirements that are either confusing or downright goofy.

A very good example out of NFPA 59A states: "Dissimilar metals shall be joined by flanges or transition joint techniques that have been proven by test at the intended service conditions."

What does one do if I have an austenitic stainless steel piping system operating at 100F & I am using integrally attached carbon steel pipe supports? It is cost prohibitive & near impossible to make the joint by flange connection, so if I use an austenitic stainless steel to carbon steel WPS with ER309L weld filler material, what "test" or "tests" do I perform to prove my "weld joint?"

My point is; be very wary and gather all requirements when it comes to Codes & Standards.

Note : We thank Tony Rangus for his comments. PWL.

On the same subject, here is an example showing how Specifications grow into Codes.
The former

AWS D3.6M:1999, Specification for Underwater Welding, 144 pages

is now superseded by

ANSI/AWS D3.6M:2010
Underwater Welding Code
Edition: 5th
American Welding Society / 10-Sep-2010 / 144 pages

It is available from our page on Welding Books.

12 - Testimonials

From: Saqib Khan
Hi,

I am very much thankful to you for sending me these tremendous knowledge full mails regarding my favorite subject (welding and related) and I hope that I will receive these in future as well from your side.

Thanks again

From: Todd R. Papora
To: Welding Advisers
Date: 06 Jun 2011, 10:33:38 AM
Subject: Thanks Elia and look forward to your further information.

Elia,

Appreciate your input and wanted to know what your thoughts [...]

13 - Correspondence: a few Comments

13.1 - It happens sometimes that a disgruntled reader, comments quite harshly to some assertion of mine considered to be not quite complete or correct. I don't claim to be always right or that certain expressions of mine could not gain by being explained more thoroughly.

I would gratefully publish any informative note from any reader that provides additional insight in good faith to advance understanding, with suitable qualifications and good manners.

I avow that I will not answer or consider comments that don't follow the above rules.

13.2 - Where are those correspondents hiding that were curious enough to ask for some information, but who suddenly disappeared without leaving a sign, after realizing that to get valuable advice they would have to be ready to pay for it?

14 - Bulletin Board

14.1 - Free Webinar: Light Optical Microscopy. Sponsored by Struers.
Thursday, July 21, 2011 2:00 p.m. EDT
Presented by George Vander Voort, FASM
ASM Webinar.

14.2 - Conference & Exhibition
Corrosion Resistant Alloys, The New Chrome-Moly Steels
August 16-17, 2011 - Crowne Plaza Charlotte Uptown Hotel, Charlotte, NC, USA
www.aws.org/conferences

14.3 - 14th Annual Aluminum Welding Conference
September 20-21, 2011 - Ft. Lauderdale, Fl
www.aws.org/conferences

14.4 - LME 2011, Lasers for Manufacturing Event
Sept. 27-28, 2011 -Renaissance Schaumburg Convention Center Hotel,
Schaumburg, Ill., USA
www.lia.org/conferences/laserevent

14.5 - See the First Day of the Rest of Your Life
http://first-day-of-the-rest-of-your-life.sitesell.com/Quark.html

14.6 - Here is the best Introduction to Site Build It! and SiteSell
http://www.sitesell.com/Quark.html

14.7 - Visit SiteSell Facebook right now and see for yourself.
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Please continue to browse down hereafter for the Mid July Bulletin.

Copyright (©) 2011, by Elia E. Levi and
www.welding-advisers.com
All Rights Reserved

Mid Month Bulletin 63 - PWL#095B July 2011

keywords: Weld Porosity, Discontinuities, Imperfections, Causes, Prevention

PWL#095B - Resources on Welding Porosity, Discontinuities, Imperfections, Causes and Prevention, Troubleshooting, Porosity Formation and Distribution, Preparation and Cleaning, Plastic Welding, Porosion in Laser Beam Welding and much more...

However well informed and expert you may be, you could certainly benefit from a vast repository of online authoritative welding information.
The following may be just what you need...

Introduction

This Mid June Bulletin #63 is now integral with and appended to the regular PWL#095 publication.

The subject of this Bulletin is a collection of Online Resources on Welding Porosity Prevention, as an extension of the article published in Section 3 above, on Avoiding Porosity in Aluminum Welding, in addition of the content of my pages on Welding Defects and Weld Porosity.

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 and to subscribe to our Welding Site Blog by clicking on the orange buttons under the NavBar in each Website page (www.welding-advisers.com). If you prefer not to subscribe, you may also click periodically on the Welding Blog button in the NavBar to see Updates.

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.

Resources

Weld Porosity Simulations
http://www.ndt.net/article/v07n07/ginzel_e/ginzel_e.htm

Weld Discontinuities - Part 1 Porosity - Incomplete Fusion -
Incomplete Penetration
http://www.esabna.com/us/en/education/knowledge/weldinginspection/Weld-Discontinuities-Part-1-Porosity-Incomplete-Fusion-Incomplete-Penetration.cfm

Porosity Problems in GMAW Welds
http://www.esabna.com/us/en/education/knowledge/qa/Porosity-Problems-in-GMAW-Welds.cfm

Defects/imperfections in welds - porosity
http://www.twi.co.uk/content/jk42.html

Low-porosity laser welding of 12.7mm thickness aerospace aluminium
http://www.twi.co.uk/content/spgvoct07.html

22 possible causes of weld metal porosity
http://www.thefabricator.com/article/arcwelding/22-possible-causes-of-weld-metal-porosity

Preventing porosity in humid environments
http://www.thefabricator.com/article/aluminumwelding/preventing-porosity-in-humid-environments

Problems with porosity in groove welds
http://www.alcotec.com/us/en/education/knowledge/qa/Problems-with-porosity-in-groove-welds.cfm

Aluminum Storage and Preparations for Welding
http://www.alcotec.com/us/en/solutions/Aluminum-Storage-and-Preparations-for-Welding.cfm

Troubleshooting in Aluminum Welding (4 pages)
http://www.infosolda.com.br/download/16DRA.pdf

Troubleshooting Common TIG Weld Discontinuities
http://www.weldcraft.com/2008/04/troubleshooting-common-tig-welding-troubles/

Troubleshooting Flux-Cored Welding
http://www.bernardwelds.com/articles/article17.htm

Troubleshooting the MIG Welding Process
http://www.assemblymag.com/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000578492

Quick and easy ways to troubleshoot common MIG welding problems
http://www.plantservices.com/articles/2010/06MIGWeldingProblems.html

Formation and Distribution of Porosity in Al-Si Welds (110 pages)
http://www.wpi.edu/Pubs/ETD/Available/etd-050806-132406/unrestricted/Legait.pdf

Porosity, Underfill and Magnesium Loss during
Continuous Wave Nd:YAG Laser Welding of
Thin Plates of Aluminum Alloys 5182 and 5754
Keyhole stability is found to play a major role in porosity formation
(10 pages)
http://www.aws.org/wj/supplement/june99/PASTOR.pdf

Welding FAQs
http://www.aws.org/wj/dec02/feature1.html

Melt flow and porosity formation in pulsed laser keyhole welding (Abstract)
http://scholarsmine.mst.edu/post_prints/MeltFlowAndPorosityFormationInPulsedLaserKeyh_09007dcc805e2eed.html

Radiograph Interpretation - Welds
http://www.ndt-ed.org/EducationResources/CommunityCollege/Radiography/TechCalibrations/RadiographInterp.htm

Welding of Nickel Alloys
http://www.keytometals.com/Article38.htm

Plastic Welding Q & A
http://www.plasticsmag.com/welding.asp?fIssue=Jul/Aug-02&aid=3603

Plastic Welding: How to Weld Plastic
http://www.buzzle.com/articles/plastic-welding-how-to-weld-plastic.html

Porosity in Thermite Welds (Presentation - 18 frames)
http://fcp.mechse.illinois.edu/media/pdfs/Chen%20presentation.pdf

Weld Discontinuities (Presentation - 74 frames)
http://www.authorstream.com/Presentation/aSGuest65041-507278-welding-defets/

Effect of Porosity Content on the Weldability of
Powder Metal Parts Produced by Friction Stir Welding (Abstract)
http://www.scientific.net/MSF.534-536.789

Penetration and porosity prevention mechanism in
YAG laser-MIG hybrid welding
http://www.norlas.com/vis.asp?fileid=535

Common Pulse-Arc Welding Applications
http://www.professionaljeweler.com/archives/articles/2003/feb03/0203pb3.html

Procedure development of laser welding of V±4Cr±4Ti alloy
(6 pages)
http://www.ne.anl.gov/facilities/lal/Publications/laser%20welding/JRMHM.pdf

Structural Steel Welding (18 pages)
http://www.ce.sc.edu/deptinfo/members/faculty/ray/web1/Ugrad/ECIV%20303/WeldingFab/s150content.pdf

Welding Practices for 2219 Aluminum and Inconel 718
http://www.klabs.org/DEI/References/design_guidelines/design_series/1205msfc.pdf

Porosity Formation in Full Penetration Welding of Thick Plates Using High Power CO2 Laser (abstract)
http://sciencelinks.jp/j-east/article/200319/000020031903A0561191.php

Joining Copper-Nickel Alloys
http://www.copper.org/applications/cuni/txt_joining_CN_alloys.html

A Novel Method for Lap Welding of Automotive Sheet Steel Using High Power CW CO2 Laser (5 pages)
http://www.engin.umich.edu/research/lamircuc/publications/4ADLAMP2006.pdf

Porosity Formation by Laser Welding in Rectangular Pulse Shape (Abstract)
http://wwwsoc.nii.ac.jp/jsdmd/2005/24-6je-1.html

Weld Defects-Their Causes and How to Correct Them
http://designdata.blog.co.in/welding-defects/

Laser Welding of AM60 Magnesium Alloy (6 pages)
http://iweb.tms.org/Mg/magtech2004/043.pdf

Double-Sided Arc Welding of AA5182-O Aluminum Sheet for
Tailor Welded Blank Applications (14 pages)
http://files.aws.org/wj/supplement/wj0110-11.pdf

Common HF Welding Defects (12 pages)
http://www.thermatool.com/information/papers/quality/COMMON-HF-WELDING-DEFECTS.pdf

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