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PWL#121 - Duplex Stainless,Storing Thorium,Thermal Spray Filler Coatings,Asking Questions,Fractogr.
September 02, 2013
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Practical Welding Letter No.121
September 2013

Best Practices for selecting and welding Duplex Stainless Steels, New Rules for Storing Thorium Containing Materials, Filler Metal for Extreme Thermal Spray Coatings, The Art of Asking Questions, Fractographic Examination (R), Friction Surfacing (R), Nitrous Oxide doping and much more...

September 2013 - Practical Welding Letter - Issue No.121

Important Notice

The Mid August 2013 Issue of Practical Welding Letter, Bulletin 88, introducing Resources on Inverter Welding Technology was not distributed by e-mail but it is available at Bulletin 88 and from the Welding Resources Page.

DON'T USE REPLY to send your messages! Use the Contact Us form instead.

This publication brings to the readers practical answers to welding problems in an informal setting designed to be helpful and informative. We actively seek feedback to make it ever more useful and up to date. We encourage you to comment and to contribute your experience, if you think it may be useful to your fellow readers.
Click on Contact Us (opens new page).

You are urged to pass-along this publication to your friends, if you like it, and if you think it may help them. If you received this from a friend and if you like what you read, please subscribe free of charge and you will also receive a bonus book on Practical HARDNESS TESTING Made Simple.
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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 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.

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.


1 - Introduction

2 - Article - Duplex Stainless Steels -
Best Practices for Selection and Welding

3 - How to do it well: New Rules for Storing Thorium Containing Materials

4 - Filler Metal for Extreme Thermal Spray Coatings

5 - Online Press: recent Welding related Articles

6 - Terms and Definitions Reminder

7 - Article: The Art of Asking Questions

8 - Site Updating: Fractographic Examination (R), Friction Surfacing (R)

9 - Short Items

10 - Explorations: beyond the Welder

11 - Contributions: Nitrous Oxide doping of Shielding Gases

12 - Testimonials

13 - Correspondence: a few Comments

14 - Bulletin Board

(Sponsored Links)

1 - Introduction

After the festivities for the Ten Years Anniversary, celebrated with the last August issue of PWL, we go back to work with a regular publication. This PWL#121 has the good chance of enjoying one more Contribution from our knowledgeable Author, Naddir M. Patel, who introduces a comprehensive overview of Duplex Stainless Steels.

It may be important for Designers, who should know when it is advantageous to use those materials for their unique properties.
As advised further down this page, the publication of a Mid Month Bulletin covering Online Resources dedicated to this class of stainless, is planned for Mid September. Interested readers should not miss it.

Storing thoriated tungsten electrodes for GTAW used to be simple enough. New rules emitted by the US Nuclear Regulatory Commission change all that. All should check how to comply with the new rules for their storing needs.

Then an article is reviewed, that explains the uses of special thermal spray filler metals to extend the operational life of components used in coal burning boilers for power generation.

Not only the availability of critical elements working at extreme service conditions is at stake, but the actual economic conduction of uninterrupted service of vital energy supplies could be compromised by unexpected failures.

Our readers are encouraged to ask questions relating to the main subjects of our website. However our long experience has shown that very few queries are written with attention to the information needed by those who supply the answers, so that they could provide useful knowledge.

That is why we include this article on The Art of Asking Questions, if the purpose of queries is to obtain clear, complete and helpful answers.
If not, then there is no need to ask at all.

In the section on the Pages of this Month we updated two reviews of interesting subjects. One refers to Fractographic Examination (R), the main source of information on the real causes producing failures in ruptured components. Only by learning the subtle cues hidden in fractured surfaces can one hope to put some order in mysterious occurrences.

The other, on Friction Surfacing (R) explains how a modification of a very successful welding process can help in producing high quality and economic coverage of protective materials on the working surfaces of essential assemblies.

The favorable outcome of judicious additions of an obscure gas to the shielding atmosphere used for welding stainless steels has been shown to improve the quality of the welding environment. Caring managers should be alert to the advantages of introducing this almost unknown ingredient in the gaseous mix.

The other regular columns will be found where expected. When looking for information, readers are advised to browse the Site Map or to type the keywords of their query in the search box appearing on almost every page of this website.

Readers are invited to ask their questions, but previously to submit them to self criticism along the suggestions outlined in our article at (7) above.

We hope you will enjoy reading, while at the same time learning some useful notions. Comments and feedback are welcomed. DON'T USE REPLY. Fill instead the Contact Us Form.

2 - Article

Duplex Stainless Steels
Best Practices for Selection and Welding

by Naddir M. Patel

Stainless Bridge

Fig. 1 - The Millennium Bridge over the River Ouse, York, Yorkshire, UK
made of Duplex Stainless Steel by
[From Wikimedia Commons - Link: Wikimedia.]
Author: Peter Church

Duplex Stainless Steels (DSS) are the preferred material of construction in the Oil and Gas and the downstream Refining industry.

This is due to their higher strength to weight ratio, good impact strength, and greater resistance to corrosion, erosion and Stress Corrosion Cracking (SCC).

They are the materials of choice whenever superior resistance to chloride pitting and crevice corrosion are required.

They typically have twice the yield strength of austenitic stainless steels.

Minimum Specified UTS typically ranges from 680 to 750N/mm2 (98.6 to 108ksi) and a typical elongation is more than 25%.

They have, therefore, extensive applications for pipelines, pressure vessels, tanks, digesters, manifolds, and risers, as well as rotors, impellers and shafts.

ASME: American Society of Mechanical Engineers.
TUV:(Technischer Überwachungs-Verein) Literally "Technical Watch-Over Association."
A German certifying body involved with product safety for the European community.

Design codes such as ASME allow for working temperatures up to 315°C, while TUV restricts
the upper temperature limit to 250°C.

Designed to combine the best characteristics of ferritic and austenitic stainless steels, DSS's by definition have a dual phase (45%-65% austenitic and 55%-35% ferritic) structure.

Their alloy matrix is made up of ferrite formers such as Cr, Mo, Si, W, Ti and Nb, and austenite formers such as C, Ni, Mn, N and Cu.

  DSS’s are thus very sensitive to the compositional balance of elements that control their dual phases.

The classification of DSS's has still not been codified, at least uniformly across the world: there is always a possibility of one DSS overlapping 2 classifications.

See a note on PREN
in PWL 54 (7)
Click on PWL#054.

Duplex stainless steels have five tentative grades or classifications and are characterized by a chemical composition based factor called PREN or Pitting Resistance Equivalent number.

PREN = %Cr + 3.3(%Mo + 0.5%W) + 16%N

  1. Lean Duplex such as S32304 (23Cr, 4.8Ni, 0.3Mo) which contains no deliberate Mo addition, with assumed PREN 26
  2. Standard Duplex such as S31803 (22Cr 5Ni 2.8Mo 0.15N) with PREN 32- 33
  3. 25 Cr Duplex such as S32550 (25Cr, 6.5Ni, 3.5Mo) with PREN less than 40
  4. Super duplex such as S32760 (25-26Cr 7Ni, 3.2Mo) and duplex grades with higher Mo and N with PREN 40-45.
  5. Hyper duplex such as S33207 (32Cr, 7Ni, 3.5Mo) which are highly alloyed and with PREN over 45.

Note: - The alloy identification is given here according to the
Unified Numbering System (UNS). See:

Material Selection Methodology:

Selection of an optimal alloy to address corrosion mechanisms efficiently is critical to addressing risks such as high replacement costs or catastrophic failure of components.

Tools include applying corrosion rate charts to determine the alloy with the greatest corrosion resistance to the materials being processed.

Subset in the best resistance to pitting based on process pH, temperature and chloride content, and specification of the maximum C % best suited to address inter-granular corrosion. That is the distinguishing factor from austenitic SS, which holds upto corrosion, but does not have pitting resistance.

Finally, zeroing in on the alloy with the best resistance to stress corrosion cracking (SCC).

As cold forming will work harden the DSS, it is good procurement practice to specify a full solution anneal, particularly if low service temperatures are foreseen.

Welding Methodology:

The challenge while welding is to obtain weld metal and heat affected zone (HAZ) properties that match the corrosion resistance and impact strength properties of the base metal.

Corrosion resistance and mechanical properties are very dependent on the phase balance and absence of deleterious micro-structures.

The ductile to brittle transition temperature is about –50°C.
The transition is not as steep as that of carbon steel and depends on the welding process used.

Flux protected processes, such as MMA, tend to have a steeper transition curve and lower toughness.  Multi run weld passes tend to promote austenite and thus exhibit higher toughness.

Welding could have a significant adverse effect on the ferrite-austenite balance in welds and HAZ.

After welding, DSS micro-structure solidify initially as ferrite, transforming, on further cooling, to a matrix of ferrite and austenite.

Fast cooling of molten weld metal will promote the formation of ferrite, while slow cooling will promote austenite formation.

Any imbalance between the phases can result in the formation of inter-metallic phases, as well as non-metallic phases, that negatively affect weld metal properties and could ultimately lead to material failure.

When DSS's are heated, two defect mechanisms come into play.

(A) Formation of Inter-metallic phases such as sigma, that occurs between 600°C-950°C. 

The formation of a sigma phase is most likely to occur when the cooling rate during welding is not fast enough.

The more highly alloyed the DSS, the higher the susceptibility to sigma phase formation. Therefore, super-duplex steels are most susceptible to this problem.

If prolonged heating below the minimum solution heating temperature is not avoided, precipitation of sigma and other phases will cause reduction in both toughness and SCC resistance.

(B) 475°C embrittlement.

475 degree embrittlement occurs when the ferrite phase decomposes into a Cr-rich phase and a Fe-rich phase in the temperature range of 350°C-525°C .

As this reaction occurs rapidly at 475°C, this process is called "475°C embrittlement". This transition temperature for initiation of embrittlement, also identified as the Curie temperature (Tc) has a critical influence on changes in microstructure that promote embrittlement.

Tc increases with aging time due to the progressive reduction of chromium in the Fe-rich matrix during spinodal decomposition.

Spinodal decomposition is defined as a micro-structural phase separation of an iron-chromium ferritic solid solution into Fe-rich and Cr-rich regions at temperatures above 300°C.

It has a time-temperature dependence.

The result is embrittlement, characterized by an increase in hardness and a decrease in material toughness shown by lower impact test values.

Welding parameters monitoring and control, especially maintenance of weld cooling rates are therefore essential to ensure ferritic-austenitic balance in welds and HAZ.

Welding parameters such as heat input, interpass temperatures and pre-heat temperatures need to be fine-tuned to ensure neither slow nor fast cooling of the weld.

Pre-heating should generally be avoided, unless condensation is present or ambient conditions are less than 5°C (41°F). In this case, depending on the thickness of the member, the pre-heating temperature should not exceed 100°C .

As 475° embrittlement can occur within a span of 7-15 minutes in a temperature range of 350°C-525°C, control of inter-pass temperatures is critical.

A general rule of thumb is that interpass temperatures in DSS's should not exceed 250°C, and those in super-DSS's should be less than 150°C. The use of forced air cooling for temperature maintenance is generally good practice.

A maximum heat input of 2.5KJ/mm is recommended for DSS's and 2.0KJ/mm for super DSS's. A lower control limit of 0.5KJ/mm is considered good practice.

Along the same lines Post Weld Heat Treatment (PWHT) is not recommended unless some phase imbalance has been detected. If the reduced strengths are acceptable, a solution anneal followed by a water quench is required; not a practical solution for welded members.

As impact strength of DSS's exceeds 200J, good impact test results of the weld are a good indication of a successful weld.

A weld run-off tested for CVN (Charpy V-notch Number, the output of a Charpy impact test) values would be a good indication of shop procedures matching PQR (Procedure Qualification Record) parameters.

Similarly the ferrite content should be between 35 and 55, with the lower control limit being preferred.

A good line of action would be to generate work instructions along the lines of ISO 3834 (Quality Requirements for Fusion Welding of Metallic Materials, in 5 Parts), so that there is no deviation from PQR parameters, especially those related to inter-pass temperatures and heat input.

A check sheet to monitor parameters during welding is not just good practice but will generate data necessary to ensure process repeatability.

From a material selection point of view, depending on the chemical composition of the DSS, this phase separation can also occur at temperatures as low as 300°C after a few thousand hours of exposure and at 600 °C with exposure of a few minutes. This could be a reason for TUV to stipulate a lower service temperature of 250°C.

Reporting Ferrite Number:
See (3) in PWL#119.

As there is a progressive reduction of Cr content in the Fe-rich phase during the ageing process, this phenomenon could be used in operational maintenance [through a PMI (Positive Material Identification - identification of materials by spectrographic analysis) or FN (Ferrite Number) testing] to detect and quantify the effects of this precipitation in duplex stainless steels.

Chemical Tanker

Fig. 2 - Delta Marine Chemical Tanker Deniz-S


Best practices, specific to DSS include:

Plasma cutting followed by machining the groove and approximately 5 mm from the edge to remove any HAZ generated during the cutting process.

To achieve a maximum of 50% dilution in the root pass and to minimize the lack of fusion defects due to the low fluidity of the weld metal, the weld preparations should have a larger included angle than that commonly used for steel.

Beveling the joint to a wide angle, creating a narrow land and setting a wide root width will enable the arc to break down the bevel and ensure complete fusion.

Welding instructions to be provided to the welder in addition to the voluminous WPS (Welding Procedure Specification) - PQR.

The cooling rate is critical to the final metallurgical structure of the weld and heat affected zone (HAZ). Strict conformance to pre-heat, inter-pass temperatures and heat input listed in the PQR is good practice.

Heat input being proportional to the current, voltage and welding speed, welders should use as slow a welding speed as feasible within the set control limits. Too high a speed, beyond the set control limit can result in cold lap.

This does not mean that tweaking of the process parameters is not possible once the process parameters have been benchmarked. Increase in productivity when using GTAW or GMAW processes can be carried out through addition of He of H2.

Helium additions have been confirmed to increase penetration and travel speeds. Small addition of hydrogen also increases the arc energy. This ensures better penetration, better width/wall thickness ratio when using higher welding speed while simultaneously addressing issues such as warpage and distortion.

As recently developed DSS’s contain considerable amounts of nitrogen, both as an austenite former and to enhance the pitting resistance, diffusion from the HAZ to weld metal and/or loss of nitrogen from the weld pool may occur.

In GMAW, GTAW & PAW, this can be reduced or prevented by use or argon/nitrogen (max. 2% nitrogen) shielding gas. Using an Argon shielding gas with 1-2%N2 has been found to be beneficial in industrial practice.

A slightly convex bead is an indication of good sidewall fusion. As opposed to a flat or concave bead, a slightly convex bead prevents center-line cracking when the weld cools.

If the root bead is too convex, fusion problems could result in the hot pass. Breaking down the ropey top of the bead and obtaining good fusion on both sidewalls will then be extremely difficult.

The presence of oxygen around the molten weld metal has the potential for defect generation. Gross oxidation can produce discoloration, metallurgical imbalance and ultimately reduction in mechanical properties and resistance to corrosion. Restoration of corrosion resistance calls for a customized pickling and passivation procedure.

In conclusion, design of welding procedures that address all geometries, proper selection of consumables, and tight process controls with emphasis on critical to quality parameters such as heat input and inter-pass temperatures and cleanliness protocols during and after welding will ensure consistent shop floor quality and traceability in the welding processes.

Note - We thank Naddir M Patel who generously wrote this instructive article exclusively for Practical Welding Letter readers.
In the next Mid September Bulletin 89 (PWL#121B), due to be published on September 16, 2013, we plan to issue a list of
Online Resources on Duplex Stainless Steels.
It is intended as a useful reference to dig deeper in this important subject.

3 - How to do it well: New rules for storing Thorium containing materials

The rules are changing, taking effect on August 27, 2013. Tungsten electrodes for GTAW containing Thorium are now falling under new rules emitted by the US Nuclear Regulatory Commission.

Check the following NRC NEWS page:

NRC Finalizes Rules on Using and Distributing Uranium and Thorium

Download the final document (35 pages) from the Federal Register, using the link given there.

It should be noted that using inverter technology permits the use of rare earth elements like lanthanum and cerium alloyed with tungsten, possibly reducing or eliminating the need of storing thoriated electrodes. See 7, PWL#120.

4 - Filler Metal for Extreme Thermal Spray Coatings

ASM Cover8

An article on the success achieved in component repair by using thermal spray to extend productive service life of steam driven power plants, was published at page 46 of the August 2013 issue of Advanced Materials and Processes (AM&P), a magazine of ASM International.

Components in the combustion gas path of coal-fired boilers suffer from corrosion and erosion. Application of CrC-NiCr coatings by liquid fuel high process HVOF (High Velocity Oxygen Fuel) vastly improves the resistance of exposed surfaces to the demanding service conditions.

Different thermal spray processes with suitable proprietary filler materials were successfully applied in global boiler applications.

An arc sprayed proprietary high chromium content nickel alloy was demonstrated to prolong the useful life of coal fired boiler tubes. A very high hardness FeCr based alloy is considered ideal for coal fired boiler environment.

An amorphous matrix nanoparticle material was effective in protecting the flue gas path from wear and high temperature corrosion.

The search for the most cost effective materials and processes in well defined applications can only be developed by experience. Suppliers of materials and equipment are probably a good source of information.

Interested readers are invited to seek the original article indicated above.

5 - Online Press: recent Welding related Articles

Weld Process Monitoring
[Requires free Registration]

Cadillac ELR Battery Structure Welded Like Airplanes
Sorry! Link deleted by the source.

Automated welding taking on added importance
Plant Engineering.

Dynetics reports 'outstanding' progress toward next generation of NASA's Space Launch System
Al. Com.

Connect - Issue 185 - July/August 2013

6 - Terms and Definitions Reminder

Brazing blowpipe is a small tube, mouth operated, used by blowing a part of a flame to obtain a small fire jet accurately directed for fine brazing.

Carbon Arc Cutting is a process used to cut into metal, using the arc from a carbon electrode.

Electrode Cap is a replaceable electrode tip used in resistance spot welding.

Flux Cutting is a process using oxyfuel gas flame, with flux added to promote cutting.

Heat Time is the duration of any one impulse in multiple impulse welding or in resistance seam welding.

Insufficient Upset is a faulty condition of flash or upset welding indicating incomplete weld.

Laser Beam Evaporative Cutting is a process variation that vaporizes the workpiece with or without inert gas to remove vaporized metal.

Positional Usability is a measure of the relative ease of application of a welding filler metal to make a sound weld in a given position and progression.

7 - Article: The Art of Asking Questions

Having seen for quite a few years a large number of letters asking technological questions, I can establish with confidence, based on personal experience, that most of them were written while ignoring the basic principles of requesting effective information.

The inquirer should demonstrate having put thought and effort into solving the problem, or at least in formulating the query, before seeking help. This is a precondition to getting actually useful help.

I assume that, at the base of every question, there is the need of knowing. Lacking that, the whole exercise is useless both for the sender and for the addressee. No questions should be formulated if there is no need for their answer.

The need may be dictated by curiosity, to base understanding on solid ground, or by any practical occurrence where a certain purpose cannot be achieved promptly and economically without first solving a pressing problem.

The inquirer should be convinced of the necessity of such an answer and should be able to explain to anybody, and especially to the inquired person, why it is so.

Looking for the reasons is not a void exercise. It helps point out the importance of the matter and prompts the inquirer to think if anything else can be done even before expressing the question.

Too many questions are formulated without a purpose or a real need. That appears clearly from the carelessness of the written text of the query.

In that case, without the inquirer being aware, the addressee cannot imagine what the answer may be needed for, so that the effort is undermined from the start.

The following elements should be clearly expressed in the query itself:

  1. Purpose of the query. It should be readily understood by the knowledgeable inquired persons, if thoroughly explained, and if all the pertinent elements describe the situation clearly enough.
  2. Formulation of the query. It should express the important points to be clarified, in a sentence ending with a question mark. Too often I am baffled by an assertion that I cannot make sense of, instead.
  3. Background. The description of the environment where the unsatisfactory outcome was obtained, if this is the case, is essential to understand if some basic requirement is missing.
    This part is the most neglected, because the inquirer instinctively tends to eliminate all additional information erroneously perceived as non relevant to the query.
  4. Description of unacceptable results if any, should be documented by photos and by additional statistical analysis, if possible. Vague wording cannot convey to extraneous persons the vivid impression registered by the inquirer.
  5. Pertinent details of the query are all the essential data that cannot be imagined by anyone not directly involved, unless they are exposed clearly and completely.
    Drawings or sketches, materials and condition, type of joint, thickness of the members, processes used and parameters, tools used, consumables etc.
  6. Introduction of the inquirer gives an idea of the professional preparation of the asking person and explains who should take the responsibility for the outcome of the operation. It could be quite disappointing for the inquired expert to explain complex processes to somebody not really involved.

As the purpose of queries is to learn and to understand for improving results, there are no short-cuts to the laborious process of investing time and efforts in preparing them to the best of one's capability.

The person receiving a well formulated query knows that it is easier to deal with and time saving, and that the answers are going to be much more effective. That is why this kind of queries are eagerly preferred.

If their purpose is to obtain practical and helpful answers, readers are urged to give a thought to these requirements and from now on, to send us preferably only well conceived and complete queries.

8 - Site Updating: Fractographic Examination (R), Friction Surfacing (R)

The Pages of this Month are reviewed and updated issues of text written a long time ago. The first is strongly connected to the engaging task of performing Failure Analysis. It is amazing how much it is possible to learn by studying the evidence told by the broken remains of a mechanical accident.

Even those not expert in this interesting discipline should at least know that the finest details of a fracture can reveal the hidden reasons for its happening. Therefore it is imperative not to obliterate those signs before an expert saw and documented them by taking meaningful photos.

An overview of the meaning of the practice and of its main tools is presented in the page on Fractographic Examination. Knowing what is looked for may help preventing irreparable damage being inflicted to delicate surface features.

For those with a detective mind this a very rewarding field of interest. Understanding the cause of failures before repairing may avoid new disappointments.

The second one explains how a variation of a successful welding process may be used to clad materials with selected alloys having special properties. It is all described in the Friction Surfacing page.

The selection of this process from the list of available options depends on the details of the application in view of minimizing the expense and assuring adequate quality.

While looking for information in this website, readers can browse the Site Map for main subject pages, the Welding Topics page for PWL Articles, and the Welding Resources page for lists of Online Links to rich sources of knowledge.

Comments, questions and feedback are welcomed. Use the Contact Us Form.

9 - Short Items

Do you know...

  • to use Duplex? (See 2 above)

  • ...the new NRC rules?
    (see 3 above)

  • ...which filler for Extreme Thermal Spray? (see 4 above)

  • ...that carbon wiring replaces copper?
    AM&P Aug 2013,
    page 14

  • ... how to spray parts in automatic cells?
    AM&P Aug 2013,
    page 45

9.1 - Micrograph is a graphic representation of the surface structure of a specimen at a magnification greater than 25×. If produced by photographic means it is called a photomicrograph.

9.2 - Ordered Crystal Structure is that of a solid solution in which the atoms of different elements seek preferred lattice positions.

9.3 - Process Metallurgy (or Chemical Metallurgy) includes science and technology of winning metals from their ores and purifying metals. Its two main branches are extractive metallurgy and refining.

9.4 - Rotary (Hearth) Furnace is a circular furnace constructed so that the hearth and workpieces rotate slowly around the vertical axis of the furnace during heating. Hot parts are removed at the fixed station, freeing space for new cold parts.

9.5 - Stringer is an elongated configuration of microconstituents or foreign material aligned in the direction of working in wrought materials. The term is commonly associated with elongated oxide or sulfide inclusions in steel.

9.6 - Tough Pitch Copper, obtained by a refining process in a reverberatory furnace, contains from 0.02 to 0.04% O.

10 - Explorations: beyond the Welder

Space Station Astronauts to Test 3-D Printing in Microgravity

Farmed Out: Overpumping Threatens to Deplete U.S. High Plains Groundwater

Sniffing Out New Strategies in the Fight against Alzheimer’s Disease

A Supergiant Star Goes Missing, and a Supernova Mystery Is Solved

Learning in a digital age

11 - Contributions: Nitrous Oxide doping of Shielding Gases

WJ Cover

A documented article published at page 43 of the August 2013 issue of the Welding Journal explains in brief why tiny addition of Nitrous Oxide to the shielding gases used for welding stainless steels can have two important environmental influences.

These additions were introduced twenty five years ago as means to reduce ozone emissions and the development of hexavalent chromium in the stainless steel welding fumes.

By reducing ozone emissions generated in the welding arc, the conditions of the welders working atmosphere are improved. Nitric oxide is entirely consumed in the welding process, by converting ozone into oxygen and nitrogen dioxide.

Moreover both oxygen and nitric oxide have the lowest ionization energies of all shielding gases, therefore increasing arc stability and heat input.

As ozone is a strong oxidizing agent, the possibility that lower ozone levels in the welding arc would correlate with lower hexavalent chromium levels was an hypothesis worth to be investigated.

Recent research proved that decreasing ozone formation correlates with decreasing hexavalent chromium formation under many of the conditions studied.

The dual effect of nitrous oxide in shielding gases for stainless steel welding should be therefore considered as an effective way to improve the working environment.

Interested readers are urged to seek the original article pointed out above and its numerous references.

12 - Testimonials

On Sun Jul 28 20:37:17 2013, the following results were submitted from the "Form 5" on

Name: Ray Brandon
E-Mail Address: removed for security
Country: United States
Organization: Seegmiller int'l
Your Task: Brazing cutting tools

Thank you very much. Good resource.

Name: Les Northrop
E-Mail Address: removed for security
Country: United Kingdom
Date: 15 Aug 2013, 05:28:15 PM
Subject: Re: spot welding

Hi Elia

Many thanks for your e-mail. I will now look into this.



13 - Correspondence: a few Comments

Here is a sample of the rudeness of the opening paragraph of letters asking for professional advice...

  • Need additional contacts in...
  • I need details on...
  • I need to weld... Kindly provide me...
  • Can we weld ...?
  • Why we should not use...?
  • I'm looking into setting up a...
  • What are the standards...?
  • Is it practical to braze...?
  • I would like to weld...
  • Laser welding of Al alloy.

... and of the ending sentence:

  • Quick response is appreciated.

None of these quoted letters meets the requirements explained in section 7 above.

14 - Bulletin Board

14.1 - ICALEO -
International Congress on Applications of Lasers and Electro-Optics
October 6-10 - Hyatt Regency Miami Resort, Miami, Fla.

14.2 - WESTEC
October 15-17 - Los Angeles Convention Center, Los Angeles, CA

14.3 - ASNT Fall Conference and Quality Testing Show 2013
November 4-7 - Rio Hotel, Las Vegas, Nevada

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