Weldability Testing for Weld Repair, Welding Copper to Stainless, Filler Metals for Beryllium Copper, Air-Carbon Arc Cutting, Transparent Welding Curtains and more...

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Date: November 2005 - Practical Welding Letter - Issue No. 27

1 - Introduction

2 - Article: Weldability Testing for Weld Repair

3 - How to do it well: Welding Copper to Stainless

4 - Filler Metals for Beryllium Copper

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article: Air-Carbon Arc Cutting

8 - Site Updating

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contribution:Transparent Welding Curtains

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

1 - Introduction

Our 27th issue of Practical Welding Letter hereafter presents new articles, news and links. You are encouraged to send us Your Questions and Feedback.

Could you possibly recommend this publication to some of your friends? Please do, and get our thanks.

Sometimes subjects are suggested by the questions we receive from our readers. One such enquiry was related to extensive weld repair to be applied to an old structure. Weldability issues must be investigated before attempting to strike the first arc. We explain why and how.

Dissimilar metal welding appears to be a subject that has appeal for some of our readers. Therefore we are continuing to present hereafter techniques and filler materials for joining additional metal combinations. This time we are dealing with Copper to Austenitic Stainless Steel welding.

Welding Beryllium Copper should not be difficult if one takes into account the properties of the material and the characteristics of the processes.

The relatively not new Air-Carbon Arc Cutting process may have specific economic advantages vs. more sophisticated and expensive processes. One should consider it for a thorough comparison, for its specific advantages.

For the Site Update we introduced a new page on Welding Projects, for those of our readers who want to use their skills to build objects in their home shop. Only be careful with the dangers, and enjoy your creativity.

The other usual departments appear where they should. We hope most of you find some interest in the items proposed.

A final heartily recommendation: do not skip the last item (14.2), follow the link. It should provide material for your thoughts and possibly open you new avenues for positive action. It worked for me... and still does.

2 - Article: Weldability Testing for Weld Repair

Weldability is described as the capability of a base metal to undergo welding by a given procedure, to provide successful service of the weldment for the designed purpose.

By this definition a material is weldable if a suitable procedure, however complex, can be developed, provided the resulting operation is more economic or attractive than available alternatives.

An introduction to some weldability problems in special purpose materials can be found in our page on Alloy Steel Welding.

Weldability tests performed in the laboratory provide qualitative results useful for comparison of different materials, processes and procedures.

When designing a new project, it is relatively easy to find suitable materials that permit application of available and economic welding processes with proper procedures.

However, when confronted with the need to provide a weld repair or a welded modification to a material lacking sufficient documentation, like an old construction, it is imperative to assess its weldability before attempting any fusion operation.

While standard weldability tests were developed for usual conditions, we will try to describe hereafter a few precautions for this specific case when no data are available on the material of an old structure.

The main problems may be lack of uniformity of chemistry and mechanical properties, non metallic inclusions and oxides, relatively high levels of sulfur and phosphorus.

If there is no way to check, then caution would suggest not to perform any welding.

Welding operations performed on an unknown material risk to initiate cracks that will undermine fatigue resistance and stability. Cracks found by suitable nondestructive testing may be most difficult and expensive to eliminate with sound repairs.

One should try to remove a narrow portion of the original material from a suitable location for metallographic and chemical analysis, but also spot tests should be requested at different emplacements with portable equipment:

1. Chemical analysis by x-ray fluorescence,
2. Hardness tests,
3. Metallographic examinations on the surface, possibly also of end sections, after polishing and etching, for obtaining replica photos of the metallurgical structure.

Once the above data are collected one should try to perform a test weld to assess the cracking susceptibility, possibly using one of a number of self restraint configurations. Descriptions and examples of tests of this kind can be found in textbooks like the following:

• AWS Welding Handbook, ninth edition, Vol. 1, page 284.
• ASM Handbook, Vol. 6, page 604.

In case of doubt, or if cracking seems to be a severe problem, the alternative to use braze-welding instead should be studied. See Braze Welding.

By this process, although the thermal cycling could produce an unacceptably hard heat affected zone, that may need to be stress relieved later, there is no fusion of the base metal thus simplifying the weldability problems. Otherwise acceptable alternatives like mechanical joining and fastening should be explored.

3 - How to do it well: Welding Copper to Stainless

Q: Can Copper be welded to Austenitic Stainless Steel?

A: Copper is readily welded to austenitic stainless steels with the Gas Tungsten Arc Welding (GTAW) by using suitable filler metals like ERCuAl-A2 or ERCu-Ni3. Welding is usually limited to thin sections, less than 3mm (0.13 in).

Buttering is not needed, especially for thin sections. The heat has to be addressed to the higher conductivity metal (Copper). Preheating at 540 ⁰C (1000 ⁰F) may be used to reduce thermal stresses on the finished weldment.

For Gas Metal Arc Welding, preferred for heavier thicknesses, the filler metals are the same as above, but one may wish to perform buttering by braze welding the stainless side to reduce dilution.

4 - Filler Metals for Beryllium Copper

Beryllium Copper alloys C17000 and C17200 include about 2% Be. These alloys are ductile and formable in solution treated (and work hardened) condition but develop high proportional limit, high fatigue strength and creep resistance upon age hardening. They are used, among other things, for springs, diaphragms, contacts and fasteners.

The high conductivity alloy C17500 is less easily welded because of its higher melting temperature and lower fluidity.

Beryllium as well as Aluminum and Nickel when present, form tenacious oxides that must be removed before welding.

Gas Tungsten Arc Welding (GTAW) is used to weld the above alloys. High frequency stabilized alternating current is preferred for use with zirconiated tungsten electrode (EWZr). Otherwise for less critical applications Direct Current Electrode Negative (DCEN) straight polarity with thoriated tungsten electrode (EWTh-2) can be used.

Preheat of up to 200 ⁰C (400 ⁰F) may be used for joints thicker than 3 mm (1/8 in). The addition of filler metal of the same composition as base metals is almost always required to provide reinforcement. However the resulting mechanical properties are inferior to those of unwelded metal, even with a complete cycle of solutioning and aging after welding.

Solutioning (annealing) followed by rapid quench is done at 790 ⁰C (1450 ⁰F). Aging 3 hrs is at 315 ⁰C (600 ⁰F) for C17000 and at 345 ⁰C (650 ⁰F) for C17200. If strength considerations permit, the weldment may be aged without solutioning. To obtain higher strength the weldment should be work hardened and the aging treatment should be modified.

Gas Metal Arc Welding (GMAW) is preferred for extensive welding of precipitation hardened material thicker than 6 mm (1/4 in), generally with the same filler as the base metals. Mixtures of Argon and Helium are used as shielding gas.

The same processes are used also for high conductivity beryllium copper alloys although with more difficulty as already indicated. Oxide formation should be prevented by using high frequency stabilized alternating current.

5 - Online Press: recent Welding related Articles

Our article on Reverse Engineering will appear on Nov. 8 in the next issue of The Fabricator. You should be able to find it at
http://www.thefabricator.com/

From AWS
To see the titles and a short note on the articles of the recent issue of the Welding Journal, see
http://www.aws.org/w/s/wj/
and click on Current Issue.

The effect of Geometric Unsharpness on Radiographs, is at
http://www.aws.org/itrends/2005/07/019/

From TWI
Arc welding robotics and automation, at
http://www.twi.co.uk/j32k/protected/band_8/ksgbm002.html

Environmental Issues Facing the Electronics Industry
http://dkc1.digikey.com/us/mkt/RoHS.html

6 - Terms and Definitions Reminder

Arc Strike is any discontinuity caused by localized application of an electric arc. It appears as remelted or heat affected material or as a surface change. In Magnetic Particle Inspection it can show up as a consequence of a spark occurring (because of incorrect technique) on the inspected item upon application of current.

Backfire is the propagation of a flame within the torch tip. Usually the flame will reappear immediately on the tip or be extinguished either by itself or by shutting the gas valves as a safety precaution.

Button is the whole nugget (or part of it) of a spot weld and its immediate surrounding material, being torn out of the test piece following a destructive test like peel or tensile test.

Coalescence is defined as the commixture, solidification and growth in a unified single body of the materials welded together.

Interpass Temperature refers to the temperature of the weld metal prior to the application of the next weld pass in a multipass procedure.

Neutral Flame generated by oxyfuel combustion is characterized by the proportions of each gas being regulated so that it is neither oxidizing (with excess oxygen) nor reducing (with excess of fuel gas).

Preform is a definite shape of brazing filler material fabricated to be located in or near a specific joint for increased productivity and better quality control.

Stub is the discarded portion of an electrode remaining once the useful part of its length has been exploited.

7 - Article: Air-Carbon Arc Cutting

This process is used successfully for gouging and back gouging, for removing defective material in welded or cast items, or fins and risers from castings, and for making bevels or grooves when preparing joints for subsequent welding.

It can be used on practically all materials, like steels and cast irons, aluminum, nickel and copper alloys. It is not recommended as preparation for welding of reactive metals. But it can be used for demolishing structures for remelting.

The cutting or gouging action is provided by blowing away, with a high speed compressed air jet, the metal melted from an arc struck between a carbon electrode and the workpiece.

Normal air pressure ranges from 550 to 690 kPa (kilopascal = 10³ N/m² or 1000 newton per square meter) (= 80 to 100 psi or pounds per square inch). Conventional shop air compressor can be used, if capable of providing between 560 to 850 liters per minute (20 to 30 cubic feet per minute).

Suitable protection should be provided against the powerful jet of incandescent molten material. No combustible materials should be around.

The power supply, similar to a welding source, should have a sufficiently high open circuit voltage. Most of times Direct Current with Electrode Positive (DCEP) (reverse polarity) is used.

With special electrodes that include rare earth materials for arc stabilization, AC power supplies of the usual drooping characteristic can be used.

Through the special torch, a compressed air jet is supplied, parallel to the carbon electrode, between it and the workpiece. The active length of the electrode, between the arc and the clamp of the torch, should be kept between 50 and 180 mm (2 and 7 in) for best results. As it burns off, the electrode should be clamped in a new position.

Electrodes are made as a mixture of carbon and graphite with a binder. After baking they result in a dense and homogeneous structure of low electrical resistance. They are usually copper coated for better contact, and provide relatively long life.

Different sizes are available depending on requirements. The larger sizes, starting from 8 mm (5/16 in), can be connected end to end by screw and socket to avoid stub loss.

Current range used depends on electrode size, which is selected according to depth and width of required gouging. The following Table provides an indication of suggested values.

Table
Recommended Current Values
for Gouging Carbon Electrodes

Electrode Size		Current, Amps
mm	in	Min	Max
3	1/8	60	90
4	5/32	90	150
5	3/16	200	250
6	1/4	300	400
8	5/16	350	450
10	3/8	450	600
13	1/2	800	1000
16	5/8	1000	1250

Although most of applications are for manual work, automatic gouging units are available for improved quality and increased productivity. These units are mounted on a carriage and follow a guiding beam for gouging or beveling thick plates to prepare joints for welding.

Alternatively, for pipe production, the units are static, while the pipe is rolling uniformly underneath.

Automatic controls operate on a signal from the arc. With constant voltage power supplies, amperage sensing controls advancing or retracting the electrode to maintain the preset current.

With constant current power supplies, voltage is controlled by a signal that advances or retracts the electrode to keep the arc length constant and to maintain constantly the preset voltage value.

The usual safety precautions used for welding and cutting should be used. The following document is available online and can be downloaded at no cost from:
http://www.aws.org/technical/facts/Z49.1-1999-all.pdf

ANSI Safety in Welding, Cutting and Allied Processes
Document Number: AWS Z49.1-99

Furthermore ear protection of a suitable and effective kind should be assured to operators because a loud noise level is produced by the high speed air jet.

8 - Site Update

This Page of the Month deals with a subject that may interest those of our readers that like to use their own welder to do their productions, practical items for Home, Garden or Farm, interesting gadgets for Hobby, or original Artistic creations for personal achievement and satisfaction.

It emphasizes a few preliminary items of caution and then provides links to a few sites providing information for making Welding Projects.
To see the page click on
Welding Projects.

To check what is new in the Website click on Site Map

9 - Short Items

9.1 - Auger Electron Spectroscopy is one of the most commonly employed techniques for determining the chemical composition of surface layers of a sample. The instrument used is a kind of electron microscope capable of ionizing the specimen with a beam of high energy electrons to excite a solid.

The technique identifies the atoms present in a layer by measuring the characteristic energies of their low energy electrons emitted upon ionization. Auger electrons are emitted from an atom with a vacancy in an inner shell.

9.2 - Dislocations are imperfections in a regular crystalline array of atoms. The creation and the movement of dislocation are studied to explain plastic deformations in metals. Dislocations were predicted theoretically long before they could be actually detected by transmission electron microscopy.

9.3 - Extensometers are instruments used for determining the change in length of specimens submitted to the action of a force. Measuring these values with adequate precision is essential for determining elastic modulus and yield point of materials during tensile tests.

Mechanical instruments are clamped upon the specimen while optical extensometers observe the relative movement of definite markings form a distance, without interfering with specimen behavior. Special heat resisting instruments are needed for testing at elevate temperatures.

Different classes of extensometers exist, for responding to specific requirements as detailed in standards like ASTM E-83 (Standard practice for verification and classification of Extensometer System), JIS B7741 (Verification of Extensometers used in Uniaxial Testing) and ISO 9513 (Metallic Materials - verification of Extensometers used in Uniaxial Testing).

9.4 - Flowforming is a process used to generate seamless cylindrical, conical or rotation symmetric bodies. To shape a part, a flat plate or a cylindrical preform is pressed against a rotating mandrel by a set of three rollers. The rollers reduce the thickness of the preform by plastic deformation and extend axially its length.

The process can be broken up in a few stages, if necessary, with interstage annealing to restore ductility. It is a near net shape economical forming technique that provides dimensional accuracy with increased material utilization, with uniform mechanical properties while eliminating the need for additional manufacturing operations.

9.5 - Radiant Tubes are used as heating systems for industrial heat treatment furnaces. Fuel is generally natural gas, but cost calculations should include also expenses relative to mandatory emission controls.

Recirculating or regenerative types can recover at least part of the heat by using it to preheat combustion air. Recuperative burners add complexity to design but provide better fuel efficiency, temperature uniformity and reduced temperature exhaust gases.

Ceramic radiant tubes of better quality and higher reliability than in the past are finding increased uses in higher temperature furnaces.

Interested readers are urged to read an article on this subject at page 76 of the September/October 2005 issue of Heat Treating Progress, an ASM International publication.

9.6 - Trip Steels exploit Transformation Induced Plasticity to develop exceptionally high mechanical properties and fracture toughness as required for very demanding applications.

Base metals are highly alloyed steels heat treated to produce metastable austenite or austenite plus martensite. Steels capable of transforming in this manner, commonly referred to as TRIP steels, are highly plastic after heat treatment.

Plastic deformation by cold working develops high tensile and yield strength because of high strain hardening rate. Part of the austenitic structure is transformed in the process into martensite, and is then followed by a tempering heat treatment.

10 - Explorations: beyond the Welder

You may recall that in the PWL 08 of April 2004 we reported in this section on the DARPA Grand Challenge a desert course race of 142 miles for robotic vehicles.

The 2004 Challenge had no winners. The 2005 has many. See the webcasts at
http://www.grandchallenge.org/

Strong New Evidence of a New, Supersolid Phase of Matter
http://www.science.psu.edu/journal/Summer2005/tocSum05.htm
and click on the first title (or on any other).

A website to watch and explore is at
http://www.worldsteel.org/

An apple a day...
http://www.news.cornell.edu/releases/Nov04/apples.nervedisease.ssl.html

New Telescope Opens Its Eyes
http://www.sciam.com/article.cfm?chanID=sa003&articleID=00006B44-F12D-135F-B12D83414B7F0000&ref=nature

11 - Contribution: Transparent Welding Curtains

The following note is based on an article published on page 29 of the September 2005 issue of the Welding Journal.

While the welder is usually well protected against the harmful effects of Ultra Violet (UV) radiation and blinding bright light, people passing by a place where arc welding is going on are generally exposed to the whole visual radiation spectrum.

For stationary welding posts, the remedy has been usually to erect opaque screens, either metallic or of heavy black plastic curtains intended to effectively block any visible danger and nuisance.

For supervising tasks the need for transparent screens to observe the welders performing their work was determined long since. Moreover, it is important to be readily alerted of conditions of accidents requiring immediate external intervention.

During the years since their initial introduction, transparent welding curtains were constantly improved, to effectively block hazardous blue-light optical radiation especially at the wavelength range of 400 to 500 nm (nanometer = 10^-9 meter). This kind of curtains are usually orange, but color alone is not a factor in determining suitability.

When considering transparent welding curtains one should check the following characteristics:

• Reduction of (invisible) UV radiation to an acceptable level.
• Filtering out of blue light radiation.
• Sufficient transparency.
• Fade resistance and flame retarding properties.

These protective curtains do not relieve welders from the requirement to wear eye and skin protective means when performing welding and cutting operations.

Manufacturers of transparent curtains should be encouraged by customer requirements to supply verifiable data on blocking capability of the proposed materials at different wavelengths of optical radiation.

Users should develop increasing awareness on the requirements specified in currently available standards which are not uniformly enforced.

Interested readers are encouraged to look at the complete article indicated above.

12 - Testimonials

From: "azhar" 'azharmahmud@mfi.edu.my'
To: Welding Advisers
Date: 04 Oct 2005, 08:20:38 PM
Subject: RE: questions

Dear Elia,

Thanks for your prompt reply. [...]

Best regards.

Azhar

From: "Paulo Domingues" 'solzaimasolar@mail.telepac.pt'
To: Welding Advisers
Date: 25 Oct 2005, 10:45:16 AM
Subject: RE: solar collectors

Hi Elia,

Thanks for your reply and attention.
[...] You may be right about my welding expertise. The only things I welded in my life were electronic components with a small soldering iron...

Best regards.

Paulo

13 - Correspondence: a few Comments

13.1 - More than once it happened that readers, willing to send a short note (always welcome) following a recent issue of Practical Welding Letter, use the Replay button. It should be understood that this practice is not recommended.

For one thing, the whole Letter is copied, and it stuffs to no use the e-mail folders of both the sender and the addressee. It is like sending a whole book for transmitting a short message hand written on the front page. Why not using the form to send us Your Questions and Feedback and typing in the short message?

13.2 - Most of the inquirers who fill in my Form 5, even if they skipped the short personal introduction at their first message, follow with at least some information with their next one. For those who do not, it means to me that they are not really interested in their own question.

14 - Bulletin Board

14.1 - ASM Materials & Processes for Medical Devices Conference and Exposition will be held Nov. 14-16 at the Park Plaza Hotel in downtown Boston.
http://www.asminternational.org/meddevices/

14.2 - You owe this one to yourself. Check the following website.
http://www.sitesell.com/Quark.html
A wealth of features and services, constantly increasing at no additional cost, are provided to non-expert like me, for one modest all included yearly subscription of less than US$ 300. I should know and I recommend it, because I use it all time with much satisfaction.

See you next time

Copyright (c) 2005, by Elia E. Levi and welding-advisers.com, all rights reserved