PWL#065 - Welding Rotators, Cutting Pipes and MPI, Fluxed Filler Metals for Gas Tungsten Arc Welding (Tig), Advanced High Strength Steels, Hot Pressure Welding, Weld Cladding, Care of Protective Clothing and more...

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1 - Introduction

2 - Article - Welding Rotators

3 - How to do it well: Cutting Pipes

4 - New, fluxed Filler Metals for GTAW

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article - AHSS

8 - Site Updating: Hot Pressure Welding, Weld Cladding

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Protective Clothing Care

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

1 - Introduction

The first issue of Practical Welding Letter for the New Year opens with a review of accessories useful for rotating cylindrical bodies in front of a welding head. It appears that different names are used for indicating the devices.

Then, in the next section, to a specific question of a reader, an answer is proposed whether Magnetic Crack Inspection has to be performed after cutting not involving flame or arc.

Covered or flux cored filler metals are not new, except that they are not used generally with GTAW. As explained in section 4 hereafter, a special situation may arise where such filler metals are recommended to solve profitably a certain problem.

Developing or selecting Advanced High Strength Steels for automotive construction may not be everybody's job. However before attempting to repair such materials by welding it would help to have an idea of the problems that could arise.

The new pages added this month to our website refer to a process (Hot Pressure Welding) and to an application (Weld Cladding) that have their use and offer benefits in special circumstances.

The care of protective clothing should affect every welder: a reference is given to a thorough article providing extensive information on the subject.

The other columns can be found at their usual place.

Use the Contact Us form to let us have your comments and feedback.
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2 - Article - Welding Rotators

Welding Rotators or Turning Rolls are useful accessories designed to keep in place and to rotate heavy cylindrical parts around a horizontal axis, at a constant and steady turning speed in front of a welding head.

Alternatively they may be rotated in steps until a needed position is reached, and then locked in place for making a longitudinal weld with a welding head mounted on a traveling carriage.

Turning rolls permit to perform circumferential welds in a vertical plane. They are also used for surfacing (cladding), or depositing by welding a filler metal of useful properties on the external or on the internal surface of a hollow cylinder.

Turning Rolls are usually arranged in sets including a pair of identical rolls, one of which is rotated by an electric motor through a reduction gear box, while the other is idle, so arranged that the distance between the rolls can be adjusted to accommodate cylinders of different diameters, and mounted on a fabricated frame of simple shape.

Usually a pair of such frames must be arranged on the shop floor at some distance from one another, to accept the cylindrical body in need of welding.

Weight capacity and diameters that can be supported are the major parameters that define rotators. Other characteristics involve wheel and surface materials, power and surface speed available.

Fit-up rolls permit alignment along horizontal and vertical directions, important especially for long cylinders.

The free turning of the part on the rolls should be ascertained before the start of the welding operation, to verify that no protrusions interfere with the motion. Also the longitudinal weight distribution should be checked to prevent overloading.

Special attention should be paid to avoid instabilities that may cause the workpiece to overturn. Minute inaccuracies of positioning may involve translation of the workpiece along its axis.

Non parallel or out of square turning rolls may cause drag forces that tend to move the workpiece unpredictably.

Although Welding Rotators are simple positioners, they should be maintained in proper service condition at all times. One should approach every job and every part with care, seriously and thoroughly, possibly following a standard check list, and learning from previous experience.

3 - How to do it well: Cutting Pipes

Q: Should Magnetic Particles Inspection before welding be performed when cutting pipes by any abrasive process?

A: The use of abrasive discs for cutting pipes (or any other item)(but not abrasive waterjet cutting) can heat the edges to quite high a temperature, unless cooling water is used to flood the place.

While mild steel will not harden (and will not crack) upon being heated by abrasive cutting even if not cooled, alloy steels subjected to uncontrolled heating can crack because of self quenching that generates untempered martensite.

Therefore, for materials susceptible to cracking, the absence of cracks due to this process should be controlled by MPI if quality production has to be assured.

Even if this requirement is not spelled out by applicable codes, it would be a matter of good workmanship to establish safe practices for the process and/or conservative measures for inspection.

4 - New fluxed Filler Metals for GTAW

Even if you know all that you need about filler metals for GTAW, you might have missed, as we did, some useful information.

An interesting thread is recently unrolling in a forum, relative to qualification Code requirements. See

http://www.eng-tips.com/viewthread.cfm?qid=228615&page=1
in the Welding, Bonding & Fastener Engineering Forum.

An inquirer asked the community about details on Qualifications performed using Flux Cored TIG rods.

Answering the doubts expressed by a skeptic reader, the inquirer makes reference to a specific filler metal with this designation, namely:

"Kobelco Flux Cored TIG rod R308LT1-5 rod. This rod is used on the root only where a back purge is impossible. The flux that adheres to the backside of the weld protects the weld from oxidization."

As another contributor voiced surprise for this material, which may not be well known by welders at large, an experienced mentor of the above Welding forum remarks that even flux covered TIG welding rods are available for the same purpose and gives the following reference:

http://www.qwpinc.net/NEW/tigwire.htm

It is never too late to learn something new and useful.

5 - Online Press: recent Welding related Articles

A kind reader called my attention to a new Forum hosted by the
ASME - American Society of Mechanical Engineers,
the Originators of the Boiler and Pressure Vessels Code
on Section IX - Welding and Brazing Qualification Community,
open to professionals and interested people alike. Those wishing to join may see:

http://peerlink.asme.org/COP/ASMEBPVCSectionIXWelding/

Understanding transfer modes for GMAW
http://www.thefabricator.com/Consumables/Consumables_Article.cfm?ID=2067

Future Advanced High-Strength Steels
Expected to Reduce Mass By 35 Percent,
Improve Vehicle Fuel Economy and Lower Emissions
Red Orbit.

Laser Welding of
Advanced High Strength Steel DP980
and Joint Property Restoration by Heat Treatment
http://asm.confex.com/asm/aero08/techprogram/paper_19356.htm

Oxyacetylene Welding (42 pages power point presentation)
http://files.aws.org/educators/Library/0000/000631.ppt

6 - Terms and Definitions Reminder

Alloy Flux as used for Submerged Arc Welding includes ingredients that, in addition to the filler metal, contribute to impart the required alloy content to the weld metal.

Bevel Face is the machined, slant surface of a bevel edge joint form.

Cladding is the application of a different material to provide selected properties (like corrosion or heat resistance) to the surface of a given substrate.

Double Flare V-Groove Weld is a weld deposited on both grooves formed when two parallel cylinders are brought into contact.

Flat Lock Seam is used to provide mechanical strength to soldered sheet metal joints by interlocking the bent overlapping edges.

Flood Cooling is used in resistance seam welding by pouring water continuously on the external surfaces of rolling electrodes and work.

Powder Feeder is a device that supplies metered quantities of powders in Thermal Spraying and surfacing.

Secondary Circuit is the portion of power supply connecting the secondary winding of a welding transformer to electrode and work.

7 - Article - AHSS

Advanced High Strength Steels are a class of modern steels that were developed during the last few decades with the purpose of reducing the weight of modern motor cars by using lower thickness sheet metal parts to obtain the required crashworthiness.

This powerful drive is promoted by the universal commitment to reduce fossil gas consumption and atmosphere pollution due to carbon dioxide emissions, by improving fuel efficiency.

The gains in strength, essential for building car bodies meeting current safety requirements, come with increased formability, a quality assuring manufacturing flexibility permitting more intricate automotive stampings with fewer parts and less joints.

Within the general name of AHSS several types are employed, called:

• DP (Dual Phase)
• TRIP (Transformation Induced Plasticity)
• HHE (High Hole Expansion)
• CP (Complex Phase)
• MS (Martensitic Steels)

The key to these developments is an increasing knowledge of the subtle influence of sophisticated thermal-mechanical processing on tiny additions of selected elements to basic steel composition.

Each one of the listed above AHSS displays a differently modified fine grain mixed microstructure that includes specified proportions of the main constituents (ferrite, martensite, bainite, austenite, pearlite).

The bulk material composition in these cases is not descriptive of the mechanical properties achievable.

The microstructure of DP steels, for example, displays a fine mix of soft ferrite phase interspersed with a high strength phase, usually martensite. The ferritic phase assures not only high formability, but also strain hardening that increases the Yield Strength.

TRIP steels include in their microstructure besides ferrite and martensite, also bainite and retained austenite. This last phase contributes more plasticity, while the strain induces its transformation into martensite.

A classic picture, titled AHSS Structure and Properties describes the relationship between Elongation (interpreted as Formability) and Tensile Strength for a number of different steels. It helps to understand the differences visually and it can be found at page 10 of the following publication:

Application and Repairability of Advanced High-Strength Steels
(33 pages)
AISI.

HHE grade steels (High Hole Expansion) usually hot rolled, are optimized for exceptional edge-stretching behavior due to better control of microscopic crack propagation during forming.

CP, Complex phase steels display an extremely fine microstructure due to their unique chemical composition and special rolling processes. The favorable combination of high strength, wear resistance, cold formability and weldability is achieved by obtaining a carefully designed balance of ferrite, bainite, martensite and precipitation hardening phases.

MS, martensitic phase steels, in the thermomechanical hot rolled condition exhibit very high tensile strength. Again these steels are described as having a balanced microstructure content of ferrite and martensite (like DP above), but in the picture above they are placed more to the right, to signify their higher strength and lower ductility.

From the description of the manufacturers it appears that forming martensitic steels is more difficult due to their low elongation, and that design limitations have to be considered. Their high strength has however considerable advantages for critical parts.

The developments related above were performed by large scale cooperation between steel producers and automotive manufacturing partners, although certain industries preferred to follow independently their own practice.

As a direct consequence these new materials are not standardized but only described by category and properties. See

SAE J2745
Categorization and Properties of
Advanced High Strength Automotive Sheet Steels
SAE International / 01-Jul-2007 /
Click to Order.

It appears that the new materials pose tough challenges to part designers because deeper consideration of formability requirements (strength increase, radiuses, springback, tolerances...) must be taken into account and therefore strict cooperation has to be established with manufacturing engineers and tool designers.

Similarly welding practices must be adapted to the peculiarities of these steels, with the development of specially modified spot welding and laser beam welding schedules.

Welding is the most important joining process considered although its applications should not reduce strength in critical locations of welded parts.

Modern car bodies are built of many different steels, as easily understood when observing exploded views (see the picture at page 5 of the a.m. publication) that indicate parts made of steel types identified by different colors.

As every type has specially optimized welding procedures, it becomes quite difficult to consider Repairability, unless exact recording of materials and repair methods is maintained.

As it is known that AHSS response to repair thermal cycles is likely to decrease strength, alternative procedures not involving welding may need to be developed to assure adequate strength of repaired structures.

8 - Site Updating: Hot Pressure Welding, Weld Cladding

The new Pages of this Month describe a process and a welding application.

Hot Pressure Welding is similar to Forge Welding in that no melting and no filler metal are involved, only high temperature and upset pressure. Heating is generally provided by oxyfuel flame, possibly through special torches.

The classic application is welding steel bars or rails, end to end. See Hot Pressure Welding.

The other page, on Weld Cladding, refers to the application of welded corrosion resistant layers on the working surface of a regular steel, by any one of a list of welding processes.

The most suitable process has to be selected depending on the requirements of the specific job at hand. For additional details, especially on the required limitations of dilution, see Weld Cladding.

To stay up to date on new subjects as they are added to the website, browse through the regularly updated Site Map or subscribe to our Welding Blog, both showing the new and the revised pages. See details under the NavBar, in the left column of every website (www.welding-advisers.com) page.

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9 - Short Items

9.1 - Controlled Rolling is a steel sheet metal hot-rolling process where the temperature of the steel, during the final rolling passes, is closely controlled to produce a fine-grain microstructure that exhibits enhanced mechanical properties.

9.2 - Corrosion Fatigue is a destructive process that causes a metal to fracture in a shorter time, under conditions of combined corrosion and repetitive cyclic loading at lower stress levels or cycles number than occurring without the corrosive environment.

9.3 - Honing is a low speed and low stress finishing process used to produce uniform high dimensional accuracy and fine surface finish, most often inside holes or cylindrical surfaces. Very thin metal layers are removed by simultaneous rotation and push pull motion of a bonded abrasive stone or stick that is lightly pressed against the surface with lower force than that used for grinding. Absence of residual stresses is verified experimentally.

9.4 - Knurling consists in impressing a design into a metallic surface, usually by pressing small, hard rollers that carry the corresponding design projecting out from their surfaces.

9.5 - Notch Rupture Strength is the ratio of the applied load at rupture to the original area of the minimum cross section in a stress rupture test of a notched specimen.

9.6 - Process Annealing is a heat treatment applied to soften metal for further cold working. In ferrous sheet and wire industries, it consists in heating to a temperature lower than the limit of the transformation range, holding for a specified time at temperature and then cooling. In the nonferrous industries, heating above the recrystallization temperatures for a time and at a temperature sufficient to permit forming.

10 - Explorations: beyond the Welder

NASA Study Links Severe Storm Increases, Global Warming
http://www.nasa.gov/topics/earth/features/airs20081219.html

'Suit Yourself' is Easier Said than Done
http://www.nasa.gov/mission_pages/shuttle/behindscenes/suit_yourself.html

One World, Many Minds: Intelligence in the Animal Kingdom
http://www.sciam.com/article.cfm?id=one-world-many-minds

Speaking of Memory: Q&A with Neuroscientist Eric Kandel
http://www.sciam.com/article.cfm?id=speaking-of-memory

Evolutionary Psychology: A Primer
http://www.psych.ucsb.edu/research/cep/primer.html

11 - Contributions: Protective Clothing Care

An interesting article was published at page 38 of the Welding Journal for November 2008. It is titled : How to Properly Care for Flame-Resistant Garments.

While care is certainly an important issue, more important may be how to select suitable protective garments for anyone involved with welding, cutting and associated processes.

The National Fire Protection Association's
Standard NFPA 70E
Standard for Electrical Safety in the Workplace
requires specific flame resistant clothing for welders.

Other related documents are:

ASTM F 1506
Standard Performance Specification for Flame Resistant Textile Materials [...]

and

NFPA 2112 Standard on Flame Resistant Garments
for Protection of Industrial Personnel
Against Flash Fire.

ASTM F1449-08 is the
Standard Guide for Industrial Laundering of Flame, Thermal and Arc Resistant Clothing.

Aluminized Clothing exhibits definite heat reflective ability, most important for workers exposed to the high heat issuing from open furnaces. However this quality might be impaired if proper cleaning practices are not followed regularly.

Wool garments are worn under primary clothing for protection from molten aluminum. Leather is still used but may be weighty and uncomfortable. Some plastic materials are not recommended.

Flame Resistant Cotton may have limitations in that the protective qualities may wash out in a number of washings. Although fit for welding they may not comply with the requirements for electric arc.

Special blends and materials known by their commercial brands are used, some with little special care.

Pending the future issuing of specific ASTM Standard Guide for Home Laundering, it is recommended to follow manufacturers' instructions and the general cleaning recommendations listed in the article quoted above, that interested readers are urged to seek for their information.

12 - Testimonials

From: arul mozhi varman
Date: 02 Dec 2008, 01:31:09 AM
Subject: Re: PWL#064

Hi Elia.

All welding newsletters are very useful. Thanks for knowledge sharing.
[...]

Many Thanks & Best Regards...

J.P. Arul Mozhi Varman.

On Mon Dec 15 02:55:33 2008, the following results were submitted from the "Form 5" on welding-advisers.com:

Name: Verma Rajamanickam
E-mail Address: removed for security
Country: Kuwait
Introduce Your Organization: Kuwait National Petroleum Corporation,
Shuaiba Refinery
Describe Your Responsibility: mechanical maintenance engineer
coordinating with various depts, especially with welding shop.
Questions and Feedback : Hi Sir,
I am enthusiastic reader of your useful and highly professional informative welding magazine for 2 years now in Kuwait.

I am also sharing this info. with other technical persons & my colleagues.

I was also teaching in a engineering college in India before coming to Kuwait.

We appreciate your knowledge in subject welding.

Regards,

Verma Rajamanickam

13 - Correspondence: a few Comments

13.1 - Approaching the Year end we found a slackening in the number and intensity of Correspondence received here at Welding Advisers. Readers were obviously busy with more urgent activities. I hope you reached your goals for 2008 and prepare your plans for taking new actions with revived forces in 2009 after the Holidays.

13.2 - To those of you who took their time for sending Greetings and Wishes and whom I failed to thank personally, please accept my apologies and thanks, and be assured that I would like to know each one of you and be of real help as much as possible.

13.3 - I am grateful that some of the readers expressed their appreciation for my work and I am pleased to hear that the information provided was interesting and useful. I would like to ask those satisfied readers to extend the information on this website and on this newsletter to their friends and correspondents. That would be great!

13.3 - A Happy New Year to all of you.

14 - Bulletin Board

14.1 - Heat Treating Society Light Metal Technology
March 25-26, 2009 - Anaheim, CA
http://asmcommunity.asminternational.org/portal/site/www/Conferences/

14.2 - International Thermal Spray Conference and Exposition (ITSC)
May 4-7, 2009 - Las Vegas, NV
http://asmcommunity.asminternational.org/portal/site/www/Conferences/

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