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PWL#107- Progress in Orbital Welding, Microfissures in Stainless Steel,Filler Metal for sour gas app
July 02, 2012
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PWL#107
Practical Welding Letter No. 107
July 2012

PWL#107 - Progress in Orbital Welding, Microfissures in Stainless Steel, Filler Metal for Sour Gas Pipeline Applications, Rail Welding Processes, Online Welding Education, Electroslag Welding, Welding Underwater and much more...


July 2012 - Practical Welding Letter - Issue No.107



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TABLE of CONTENTS

1 - Introduction

2 - Article - Progress in Orbital Welding

3 - How to do it well: Microfissures in Stainless Steel

4 - Filler Metal for Sour Gas Pipeline Applications

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - Rail Welding Processes

8 - Site Updating: Electroslag Welding (R), Underwater Welding (R)

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Online Welding Education

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board


1 - Introduction

What better way to open this 107th issue of Practical Welding Letter than by proposing something new to the readers' attention? We open therefore by quoting an article reporting on serious efforts to develop orbital welding for thick wall pipes.

It seems a hot subject, given the forecasts of several new power generation installations, and that explains the range of efforts being devoted to finding the most cost effective solutions. The race is still on.

It should not come as a surprise, therefore, that two other articles, related more or less to the same issue, are also published in that journal, but only their title is reported here.

Then another subject, that of the appearance of Microfissures while welding Stainless Steel, receives again the expert advice of Damian J. Kotecki, whose inexhaustible knowledge and experience continues to amaze readers seeking practical solutions.

On filler metals this time we can only point to a commercial company assuring that they developed an adequate response for those dealing with pipelines intended to transport sour gas. No recommendation is intended or implied, but interested readers may wish to check on their own if real benefits are available to them.

Section 7 reports on continuing development programs devoted to improve service performance of rail welding, subjected to more severe requirements due to increased traffic of heavier loads.

Especially those whose daily work is far from rail problems may discover mind opening issues, including the vast range of failure modes and the amount of work invested to understand the root causes and the best ways to overcome the difficulties, and how this search drives the development of new steel types.

Our website update effort needs deep revisions of many pages, to add new information and to correct older and questionable assertion. Like every serious work it takes a lot of time. For this month two updates were achieved.

One updated page deals with Electroslag Welding, tested to verify its adequacy also for rail welding. The other page is a review of Underwater Welding, recently enriched also by the new Underwater Laser Beam Welding.

Before adding new pages the website revision process will continue, to improve the relevance of the information presented in the existing chapters.

When looking for specific subjects, besides the Search function appearing in most pages, and the FAQ page, readers can use the Site Map or the Index Page.

Readers are welcome to send us their comments and feedback, using the Contact Us form.


2 - Article - Progress in Orbital Welding

Orbital Welding is a well known welding technology used for joining end to end relatively thin tubes and for tube walls in heat exchangers. It used to be a mechanized version of Gas Tungsten Arc Welding (GTAW), that enjoyed remarkable success in a vast range of practical applications.

What about extending the Orbital Welding benefits also to the realm of thick pipe welding? Any advancement capable to improve quality and productivity when joining heavy-wall alloy steel pipe in power plant construction, would have considerable impact on the economics and on time scheduling of new projects.

The limited productivity of present time technology has to do with the fact that it is labor intensive. Manual gas tungsten arc welding (GTAW) is used for root and hot passes, which are followed by shielded metal arc welding (SMAW) for the many fill passes that deposit large amounts of weld metal. Furthermore, a quite large regular bevel is needed for filling the gap and for grinding out defects and re welding if necessary.

An Article titled Using On-Site Orbital Welding for Power Plant Construction was published in the June 2012 Issue of the Welding Journal at page 51. The introduction of automated orbital welding of heavy wall pipe during on-site construction of power plants has potential for maximum benefits, if two major issues were addressed successfully.

First the total automation of the Gas Metal Arc Welding process (GMAW), including Automatic Voltage Control and automated welding sequence should remove completely the need for repairs.

Second, the introduction of a narrow groove instead of the standard bevel, would reduce dramatically the amount of weld metal to deposit per joint.

The quoted article reports on practical experience gained with improved equipment of Gas Metal Arc Welding (GMAW), using already prepared wide bevel joints. Operator training enjoyed special attention, together with the constant presence of maintenance personnel from the equipment supplier.

The article concludes that the Automatic Orbital Welding employed in the reported demonstration proved the various advantages over manual weld process. Relieving welders from fatigue and lapses of attention, improves welders well being and reduces the chances of causing defects that need to be repaired.

Interested readers are urged to seek the original article at the reference indicated above. The quoted article, notwithstanding its importance as a development stage in progressive technology is not yet ready for off the shelf implementations.

In the same Journal two other related articles can be found:

Hybrid Process Welds Thick-Walled Tubes (pg 55)

New processes and Metal Cored Wire combine to Improve Pipe Fabrication (pg 69)

For completeness one should add that a development project called Laser/GMA Hybrid Pipe Welding System was carried out at the Penn State Applied Research Laboratory working for the Center of Shipbuilding Technology, and preliminary results were published at
http://www.cnst.us/Projects/hybrid_welding.html

The report states that "Successful implementation will serve as a stepping stone toward eventual development of hybrid laser/GMA orbital pipe welding systems, further broadening [...]" From this one should conclude that the commercial application is still not available.

However other commercial companies like Precitec, Esab, Lincoln etc. may have suitable systems available, so that whoever is interested should perform a thorough search to check the present situation.

Two other processes may in principle compete with the application described in the article, if they are modified to suit field operation, as opposed to shop fixed installations.

1 - EB (electron beam) welding of large components without a vacuum chamber - (from PWL#092)
TWI.

2 - Friction Stir Welding of Steel Pipes (video) - (from PWL#078B)
MSM.

Readers with personal experience in welding thick pipes are invited to contribute their thoughts on the matter.


3 - How to do it well: Microfissures in Stainless Steel

It is not the first time that I recommend to the readers the notes that Damian J. Kotecki publishes on the Welding Journal. I believe that a collection of those questions and answers, would be a most instructive reading.

This time I propose to the readers' attention the note published at page 14 on the Welding Journal of November 2008. A worried reader asks about the causes for the appearance of microfissures in the bend tests of welded specimens of type 310 and 330 austenitic stainless steels.

It should be noted that normally the presence of small (less than 0.125" = 3.18 mm) openings is allowed by the bend test requirements. Nevertheless there could be reason for concern.

The Author explains that it is almost impossible to avoid their presence in completely austenitic structures devoid of any ferrite, despite trying to reduce their number by using low heat input and higher purity filler metal.

A suggested alternative to the bend test, is a normal tensile test to be performed on a longitudinal weld specimen and to be stopped at about 10% strain. The article reports on research published in the Welding Research Council Bulletin 502 (www.forengineers.org), which is reassuring, in that also microstructures containing limited microfissures are known to perform well in service.

Interested readers are urged to seek the original article.


4 - Filler Metal for Sour Gas Pipeline Applications

The following note is reported from a commercial supplier. No endorsement or recommendation is implied or intended. The information is reported for those readers with special needs who may be interested in exploring if it may help them.

Hobart Brothers announced that it has developed a gas-shielded metal-cored wire specifically to improve welding performance and quality on sour gas pipeline applications. Metalloy® 71 SG wire features high deoxidizer levels that are capable of welding through mill scale and still producing consistent quality welds.

The wire also offers excellent wetting characteristics to ensure smooth weld beads with uniform tie-in and help minimize weld defects and their associated rework. Additionally, it generates a low hydrogen weld deposit - 3.3 ml per 100 g of weld metal - to help mitigate cracking.

Metalloy 71 SG wire is designed for welding in flat and horizontal positions, and can be used in short circuit or pulse applications. It is also usable for welding on non-alloyed and fine grain steels, rail car and heavy equipment manufacturing applications and with robotic welding systems.

Hobart Brothers offers the Metalloy 71 SG wire in .045-inch diameter and recommends it for use with a shielding gas mixture of 75 to 95 percent argon and a balance of CO2. It provides a tensile strength ranging from 70 to 87 ksi and a yield strength ranging from 58 to 80 ksi. Specific values depend on the exact shielding gas balance used. It also provides excellent Charpy V-Notch values, ensuring good toughness at temperatures as low as -76 degrees Fahrenheit (-60 Celsius).

METALLOY® 71 SG - AWS A5.18: E70C-6M H4
http://www.hobartbrothers.com/uploads/pdf/datasheets/Metalloy71SG.pdf


5 - Online Press: recent Welding related Articles and Video

Sabre forges partnership with college
SC Journal.

Robotic Welding Equipment with Central Fume Control
http://www.mmsonline.com/articles/robotic-welding-equipment-with-central-fume-control

Welding Procedure Specification [for plastic (Polyvinylidene fluoride) socket]
http://engstandards.lanl.gov/esm/welding/welding_specs/7000-xxxx-PVDFsocket.pdf

Strategic Planning: More Than A Mindset
GAWDA.

Tech Tip: Welding Stainless Steel for Marine Environments (Lincoln Video)
http://www.youtube.com/watch?v=ANFXXKMRhfc


6 - Terms and Definitions Reminder

Induction Work Coil is the inductor used to heat the work for welding, brazing or heat treating.

Low Pulse Time, a term applicable to pulsed power welding, is the duration of the low current pulse.

Oxide Film refers to process and procedure related discontinuities resulting from improper preparation or by insufficient shielding or improper flux.

Pulsed Laser describes a laser that outputs controlled short power pulses.

Round Edge Shape is a type of edge in which the surface has a curved shape.

Surfacing Weld as opposed to brazing or thermal spraying, is a weld applied to a surface or substrate, to deposit a layer presenting improved properties, or to restore dimensions.

Taper time is the interval during which current increases or decreases continuously according to a predetermined slope.

Wire Flame Spraying is a thermal spray process where the surfacing material is supplied to the torch in wire form.


7 - Article - Rail Welding Processes

The most used processes for joining rails end to end are presently two.

The thermite process, (see Thermite Welding), is based on an exothermic reaction between aluminum and iron oxide that produces a mass of superheated molten steel, to be poured in a mold prepared around the rail gap. Upon solidification the rails are welded.

The second process, described as flash butt welding, (see Flash Welding Processes), is done by heating the rails ends, placed one against the other, by the passage of an electric current, and simultaneously forcing them together with a powerful press.

Both processes have a long history of successful applications. The first is criticized because of the high turbulence generated in the flowing molten metal, that produces porosity.

The second, although generally producing joints of higher quality, is made with bulky equipment, not easily portable along the rail track. It is also censured because it consumes rail length.

Continuing efforts are done to improve the shortcomings of both. Development work is active within various organizations.

Adaptations of a different process, Electroslag Welding (ESW), (see Electroslag Welding), have been implemented. ESW consists in placing an open mold around the abutting ends of two rails with a certain gap in between.

An electric arc struck between an electrode and one of the rails under the cover of granulated flux, melts the electrode end, and generates a molten metal pool that sinks to the mold bottom. Fused flux floats above the molten metal and protects it from the atmosphere.

The heat melts also the exposed rail end surfaces to produce sound welds. As the mold volume fills with molten steel, the welding head is slowly removed toward the top.

The process is stopped once the required volume is replenished, the molten metal slowly solidifies and the joint between the rails is completed. There is much less turbulence than in the first process, because the cleaner molten steel is added drop by drop. Relative to the second process it is less costly and more portable.

It is considered advantageous because of certain benefits like non consuming rail, being cleaner and less turbulent than the exothermic process. Relative to flash butt welding it should be preferred because of more portable, less costly equipment. One additional attractive feature of ESW is that the weld chemistry can be modified during the process.

In the original ESW process, made to weld heavy plates in vertical position, fixed or moving water cooled shoes delimit the joint around the abutting plates.

Successful developments have been completed, and tests have been run to assess the quality. Testing included hardness, tensile strength, impact toughness, inclusion counts, microstructural characterization, chemical composition and 4 point bends.

Parameters investigated were guide tube configuration, gap dimension, welding conditions, cooling methods, preheat and cooling shoe configuration.

The economic viability is still undecided, but further work is still done and planned.

By reviewing the open information one can see that the research is driven, in the USA, by the huge interests involved with rail transportation. Among the subjects studied are automated non destructive testing methods, research in fatigue failures, improvements in steel type and quality, and railroad repair methods.

It is not surprising that numerous development tasks were programmed in the last few years to be budgeted, planned and performed.


8 - Site Updating: Electroslag Welding (R), Underwater Welding (R)

The revised Pages of the Month are quite visited ones that needed updating.

One page refers to a rather special process, successful for making one pass welding of thick plates. It was also tested for joining rails, as reported above in section 7. The joint is held in the vertical position, and the weld is progressing from bottom to top.

The page with this title is found at Electroslag Welding.

The other page describes a few different processes that have in common the characteristic of being used for welding marine or nuclear structures immersed in water. The quality requirements are constantly revised to reflect more exacting service usage, and process improvements try to meet them.

The trend is to develop completely automated units, capable of operating at ever increasing sea water depth, with remote human assistance and control from a safe distance. However for the time being, welders divers are still much in demand for promising and rewarding careers.

This page is available at Underwater Welding Processes.

All the website pages links can be found in the Site Map or in the Index Page.


9 - Short Items

9.1 - All-Weld-Metal test specimen is one that its tested portion is completely weld metal.

9.2 - Bulging means expanding the walls of a hollow body with an internally expanding device. Also the process of increasing the diameter or the outer walls of any shell whose walls were previously straight.

9.3 - Closed Dies are designed to restrict the forging or forming flow of metal to the cavity within the die set.

9.4 - Double Aging is performed at two temperatures to control the type of precipitates formed from a supersaturated matrix in order to obtain the desired properties. The first aging treatment is usually carried out at higher temperature than the second.

9.5 - Etching means exposing the surface of a metal to preferential chemical or electrolytic attack, of different features (grains, borders, phases) in order to reveal structural details for metallographic examination.

9.6 - Nibbling is contour cutting of sheet metal by use of a rapidly reciprocating punch that makes many small cuts, superseded by CNC (Computerized Numerical Control) driven laser cutting.


10 - Explorations: beyond the Welder

Oldest Cave Paintings May Be Creations of Neanderthals, Not Modern Humans
SA1.

Charismatic Megaparticles Might Hint at Dark Matter, and Much Besides
SA2.

Astronomers Catch Video of "Near-Miss" Asteroid
SA3.

Earth Summit: A Report Card to Preview the Rio+20 Mega-Conference
SA4.

Shoreline Science: Exploring the Erosive Energy of Waves
SA5.


11 - Contributions: Online Welding Education

AWS’s American Welding Online is a new initiative designed to provide to interested people the opportunity to reach welding education at their own pace and schedule.

An authoritative seminar on Welding Fundamentals, developing in a course of approximately 14 hours, is now available online. In the presentation, published on the Welding Journal, one reads that the course provides a fundamental overview of welding, focusing on the most widely used welding processes.

The introduction goes on to explain that Fundamental instruction is presented on welding theory, equipment, safety, weld design, metallurgy, welding inspection, and quality control.

Find more details at:
http://awo.aws.org/seminars/welding-fundamentals/
Once in that page, by clicking on "What does the seminar cover?" you get the list of the titles of the 11 Modules in which the course is divided.

Another seminar is available on safety issues. It provides basic instruction, articulated in 15 Modules, and students can join the Completion Exam and receive a Certificate. See details at:
http://awo.aws.org/seminars/safety/

A further seminar is dedicated to Online Certified Welding Sales Representative. Instruction is divided into 12 Modules covering all important aspects. Upon completion of the course an examination is available to those students requiring a Certification. Details at:
http://awo.aws.org/seminars/cwsr/

A most interesting series of 11 Videos taken at last year Educational Annual Program from the Fabtech Conference, is open to all at
http://awo.aws.org/conferences/2011-educational-annual-program/

Amazed by watching the second in the series, a video on e-learning in general, titled "E-Learning on a Budget", I recommend it to all who have an interest in learning and in teaching, and can spare an hour. Watch it at:
http://www.youtube.com/watch?feature=player_embedded&v=Dcuv_XpTzZw#t=0s

The fourth Video in the series, titled Adams Memorial Lecture by Prof. Bryan A. Chin, Ph.D., of Auburn University, explains in detail the fundamental changes that were introduced in the syllabus of engineering courses, within the four decades he was involved in teaching.

Curious readers, especially those with teaching responsibilities, may wish to browse also through the other videos presented in the above page.


12 - Testimonials

From: Sam Nistala
To: Welding Advisers
Date: 04 Jun 2012, 12:42:34 PM
Country: United Kingdom
Subject: Re: Thank you Sir for download link
Thank you very much.
Your web site is fantastic.
[...]
many thanks
sam nistala


Name: Daniel Rybicki
E-mail Address: removed for security
To: Welding Advisers
Date: 15 Jun 2012, 01:19:32 PM
Country: United States
Organization: Government
Task: Welding Engineer

RE: Hardness Book

Thanks Eli. It worked and I retrieved a copy.

And thanks for all your help over the years.


13 - Correspondence: a few Comments

While I receive sometimes appreciative words on my website, I miss the opportunity of having some sort of fruitful dialog with my readers. I know that the proper place for such exchanges should be possibly within the social media distribution channels.

However nothing forbids you from jotting a few lines of comments, of suggestions, of criticism on the things you know best and on what hurts you. You have certainly interesting points of view and your contribution, together with the reactions of other readers could add thoughts to all of us.

You are sincerely invited to have your voice heard. Please use the Contact Us Form. Thanks.


14 - Bulletin Board

14.1 - The 7th International Seminar on Advances in Resistance Welding
12-14 September 2012, Busan, Korea
http://www.swantec.com/7th-Seminar-2012-Busan_Preliminary-Program.pdf

14.2 - ICALEO, 31st Int’l Congress on Applications of Lasers and Electro-Optics.
Sept. 23–27. Anaheim Marriott Hotel, Anaheim, Calif. Laser Institute of America. www.icaleo.org

14.3 - Laser Materials Joining Solutions - Laser Welding & Joining Workshop
October 23-24, 2012 - Renaissance Schaumburg Convention Center Hotel
Schaumburg, Illinois USA
www.lia.org/laserwelding

14.4 - Visit Now the BlockBuilder 2 Page

Get Ready for a New Start!


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