American Welding Society Forum

Topic Argon...Helium...which is "hotter", yes this is a trick ? By Stephan Date 12-13-2009 00:48

Dear Allan,

longer time ago since I’ve been here.

Then, finding a minute to take a breath and making a short sidestep into the worlds largest welding forum (© Henry), I directly bump into this – your – wonderful question.

And yes… it’s ‘tricky’, but rather less a ‘trick’.

Instead of asking: “Which of the following shielding gases gives the highest arc temperature?”, perhaps the question should have been asked like:

“Which of the following shielding gases gives the highest electrical conductivity?”

Then, I am sure all of your students have answered: Argon. And in this coherence one could have said. The better the electrical conductivity, the less the resistance and the higher - eventually - the kinetic energy input to the work.

Great information, to say the least, coming from all of the appreciated fellows. In particular I mean however, the key lies in two specific sections of Henry’s ‘dissertation’. That is where he states:

[quote]

“Well, which welding process are they referring to,…”

[unquote]

and:

[quote]

P = I(Ei + Ec + Ep)
Where:
P = power, W
Ec = anode voltage, V
Ec = cathode voltage, V
Ep = Plasma voltage, V
I = current, A

[unquote].

Let’s suppose we are dealing with GTAW and the tremendous number of variables, when it comes to an inclusion of metal vapours etc., shall be neglected.

Then we should transform the expression of Henry into the expression derived by SCHOECK et al in 1963 [1], saying that the total energy input Q is:

Q = I (Va+VKT+Vw)

I = Welding current
Va   = Voltage drop
Vw   = Anode work function
VKT = Thermal plasma energy

This expression has now been used by GLICKSTEIN [2] who has thoroughly investigated the physical background of different thermal effects of different shielding gases (Ar, He, Ar+He, He+Ar, Ar+Al-vapour, He+Al-vapour).

Hence, let me hereafter state what GLICKSTEIN has found out by his own and by using the results of many other famous researchers.
The secret lies in the gaseous properties of Argon and Helium. It is well-known that the main portion of the kinetic energy in arc welding is carried by electrons. Thus, according to GLICKSTEIN, it may be supposed that the current density distribution ‘determines the distribution of the energy input to the weldment’. He explains that Argon has – due to the lower ionisation potential vs. Helium – a ‘higher electrical conductivity at lower temperatures’. Anyway, Helium again has a lower mass and thus, he describes Helium to have a higher thermal conductivity vs. Argon. GLICKSTEIN has investigated a 100 A GTAW arc and has calculated – based on experimental measurements – the electric fields for both gases as 15 V/cm for Helium and 7.7 V/cm for Argon. Thereby he explains the ‘broader and higher arc discharge temperature distribution’ for a Helium arc compared with an Argon arc. This, due to the so-called ‘energy source term’ is based on the temperature dependent thermal conductivity (sigma) and the square of the electric field (E) or:

Sigma(T)*E²

what again is explained to increase the radial energy transfer. And this, we all know from the practice, is true, since a Helium arc shows a more ‘diffuse’ appearance compared with an Argon arc. Thus, we may confirm what such great people like GLICKSTEIN et al have theoretically established long ago.

So far so good. To explain the differences in both energy and temperature distribution in a 100 A Argon and Helium arc it is provided that the values for the variables in the first expression, as stated above, are:

Va_Ar ~ 2.99 eV (anode drop for Argon)
Va_He~ 4.71 eV (anode drop for Helium)
Vw   ~ 4.5 eV (work function of Tungsten)
VKT ~ 1.2 eV (thermal plasma energy)

Now one can calculate:

Q_Ar   = I * (2.99 + 1.2 + 4.5) = 8.69 * I

Q_He   = I * (4.71 + 1.2 + 4.5) = 10.41 * I

For a given current one obtains thus an approximately 20% higher thermal energy input for a Helium arc compared with an Argon arc.

So, one may conclude, that no really significant difference in the ‘temperature’ between an Argon and a Helium GTAW arc has been found. But a quite significant distinction in the energy content of both arcs could be evaluated. To emphasize this, I would like to directly quote GLICKSTEIN [2]:

“The greater energy input associated with the helium welding arc compared to an argon arc at the same current does not result from a ‘hotter’ temperature as commonly believed. Experimental measurements of the electric fields and analysis of the potential drop associated with each gas discharge show that the greater energy of helium can be attributed to a larger anode drop potential relative to that of argon arcs.”

Nicely said and truly hitting the famous nail on the head.

Isn't it good that the world has so tremendously intelligent people like Glickstein, Schoeck et al..?

Stephan

References:

[1] Schoeck, P.A. (1963), “An investigation of the anode energy balance of high intensity arcs in argon”, in: Ibele, W. (Ed.), Modern developments in heat transfer, Academic Press, New York and London, p.353-478

[2] Glickstein, S.S., (1980), “Arc modelling for welding analysis”, in Arc Physics and Weld Pool Behaviour Conference Proceedings, Vol. 1, 8–10 May 1980, London, The Welding Institute, Cambridge, p. 1-8

EDIT: I did forget. Merry Christmas and a Happy New Year to you, Allan, and to all of the others!

Topic 304 Stainless Arc Wandering? By ssbn727 Date 10-16-2009 14:27

Adam is more than likely welding some high purity or ultra-high purity lines that require very stringent controls in the amount of sulphur and/or manganese content in order to prevent such problems as well as avoiding certain discontinuities that may result from having higher than recommended levels of these elements in both the base/parent metal as well as the filler material and more than likely with 308, there's too much of a percentage of either or both of those elements I mentioned previously... Remember this usually occurs when one is GTA welding via the use of orbital equipment and usually in high purity or ultra-high purity applications. ;)

He may also be experiencing a problem with the ppm's (Parts Per Millions of Oxygen atoms in the shielding or purging gas) of Oxygen in either the shielding or purging gas being too high which can also cause some undesirable effects in both the arc consistencey as well as the desired shape of the weld pool and the surface conditions of the face of the weld also when in combination of having higher than recommended levels of both sulphur and manganese as well. However, the only way to find out is by process of elimination and as he noted before in his initial post, I believe that Adam has found the cause of the problem he was previously experiencing and no longer faces this issue.

The bottom line is that one needs to read the article I posted in the previous post before this one in order to get a better sense of what I am alluding to in this one. :) :) :)

Here is just an example from arc Machines how the manufacturing process of the materials used alone can make a significant difference in the quality of the weld deposit...

Metallurgical Aspects

Sulfur. Research has shown that elements such as sulfur and oxygen, which cause the temperature coefficient of surface tension to be positive, result in a weld puddle in which heat is transferred from the perimeter inward and downward with good penetration of the weld bead.

Removing sulfur and oxygen, either by refining or by the presence of elements that combine with sulfur or oxygen, such as aluminum, has an opposite effect on penetration. In the latter case, the temperature coefficient of surface tension becomes negative, producing a wide, shallow weld with poor penetration and a tendency toward concavity (see Figure 2). Other elements, including manganese and silicon, have slight effects on penetration, but sulfur has by far the greatest effect.

However, sulfur in stainless steel combines with manganese to form nonmetallic inclusions called manganese sulfide (MnS) "stringers." When tubing is passivated or electropolished, the stringers leave pits in the 0.25- to 1.0-micron size range. The tiny pits show up on SEMs (scanning electron micrographs) used to screen tubing samples for surface finish qualification. Since pitted surfaces are undesirable for high-purity applications and are typically the first places to show evidence of corrosion, tubing manufacturers and distributors have rallied to drive down the sulfur content of 316L tubing.

The American Society for Testing & Materials (ASTM) has recently added a supplement for Pharmaceutical Quality Tubing to the ASTM A270 specification for Seamless and Welded Austenitic Stainless Steel Sanitary Tubing. The supplement (S2) limits the sulfur content of this grade to 0.005 to 0.017 percent. These values allow for ease of welding with lower MnS inclusions than would be found at the higher sulfur values of 316L.

With moderate to high sulfur content, type 316L is easier to machine than the low-sulfur materials, so it is favored by some fitting manufacturers. Thus, engineers, contractors, and welding personnel must take care in ordering tubing and fittings and record and track material heat numbers during fabrication to avoid costly problems.

VIM/VAR and EBR Materials: 316L bar stock made by the vacuum induction melted plus vacuum arc remelted (VIM plus VAR) processes that contains a very low level of sulfide and other inclusions is now available. This "clean" material, called 316L-SCQ™, is intended for use for ultraclean gas supply components such as valves, regulators, fittings, glands, gaskets, pipe, and tubing. The base metal has a finer, more uniform grain structure than conventional type 316L, and orbital welds on this material have a much smoother appearance.

Stainless steel produced by the electron beam refining (EBR) process has been used experimentally for special ultra-high-purity (UHP) semiconductor applications. This EBR process uses entirely virgin materials in the melt, producing an unusually clean material. Manganese and other trace elements are reduced to very low levels, resulting in reduced stringers and improved corrosion resistance.

This material also has less of a tendency to discolor from oxidation during welding. The blue "halo" that typically appears on either side of a weld on some heats of material does not appear on properly purged EBR material.The surface of the EBR weld bead is significantly smoother than welds on even VIM/VAR material. The dendritic crystallization structure of welds on typical argon oxygen decarburization (AOD) and VIM/VAR materials form a rough surface with minute projections seen at high SEM magnifications.

One recurring problem with conventional type 316 is the tendency for some heats to form slag islands or weld dross on the OD or ID weld bead. A change in shielding gas or weld parameters may reduce this problem, but it is difficult to eliminate entirely. Slag typically contains silicon and compounds of calcium and aluminum, which are added to standard melts to remove impurities. The EBR melt is very low in impurities, so additions to remove them are unnecessary, and the slagging problem is nonexistent.

Stainless steel's lack of consistent weldability from heat to heat has kept orbital GTAW from becoming a fully automatic process. Weld programs for each tubing diameter and wall thickness are entered into the power supply memory. A weld program or schedule will produce consistent uniform welds on a particular batch of tubing, but if tubing of a different heat number is introduced, some adjustment of amperage may be required, and parameter verification through test coupons is advisable.

Controlling the chemical composition of 316L materials with advanced refining technologies might eventually minimize heat-to-heat variations in penetration and allow orbital GTAW of tube to become a nearly automatic process. This will save the production time currently spent on optimizing weld programs for individual material heats.

Welding and fabricating tubing may result in a loss of corrosion resistance relative to the unwelded base metal. The HAZ of welds has been implicated in the formation of rouge, a rust-like film containing the products of corrosion, in pharmaceutical water systems. Contamination of stainless steel tubing, particularly with carbon, carbon steel, or chlorides, can severely affect corrosion resistance. Heat tint oxidation produced during welding also severely reduces the corrosion resistance of stainless steel, with the loss of corrosion resistance proportional to the oxygen concentration of the purge gas.

After fabrication, pharmaceutical piping systems are typically passivated with nitric acid or a mixed chelant solution before being placed into service. Passivation, however, is a relatively mild treatment and only affects the outer surface layer to a depth of 30 to 50 Å. If the heat tint extends below this level, and it has been shown to extend to a depth of about 1,000 Å in severe cases, then passivation will not be able to remove the heat tint. For passivation to be effective, the surface must be clean.

Both welding and fabrication must be done carefully to limit damage to levels that can be corrected by passivation. Recent studies have shown that welded 316L tube samples purged at oxygen levels of 108 parts per million (ppm), 8 ppm, and less than 0.1 ppm show visible effects of corrosion in proportion to the levels of oxygen in the argon purger.
The amount of heat tint and corrosion was slightly greater on mechanically polished tubing than on electropolished tubing of the same heat number. This is most likely due to the larger surface area on mechanically polished tubing, which has a greater affinity for oxides.

Orbitally welded 316L tube samples were compared to previously studied unwelded tube samples and found to have comparable pitting potentials(2). Samples passivated with either mixed chelant solutions or with nitric acid were found to have significantly higher pitting potentials than unpassivated samples, whether or not they had been welded (see Figure 1 and Figure 2). The exception to this was the group of mechanically polished tubes welded with the lowest-purity purge gas (108 ppm oxygen). These samples had active polarization curves, indicating a severe loss of corrosion resistance. This severe effect was not observed on electropolished tubes purged with the low-purity gas.

The most heavily corroded parts of the welds subjected to corrosion testing were the areas of overlap and downslope. Since these areas were welded twice, it suggests that the additional heat input caused a localized reduction in corrosion resistance and indicates that careful control of the heat input during welding is important for corrosion control.

Manual Tacking. For some applications, tubing is manually tacked in place with a hand-held GTAW torch to align the tubes or fittings for orbital welding. If this is done, the inside diameter (ID) of the weld joint must be purged during the tacking process. An orbital arc may deflect around an unpurged tack and cause a lack-of-penetration defect, and oxidized tacks may become corrosion initiation sites. Look! read this article:

http://www.arcmachines.com/appPages/fabri02.html

Then read this... Material weldability. Different heats of stainless steel tubing can make it difficult to weld by automatic fusion welding techniques. ASTM specifications for each type of stainless steel such as 304, 316, 304L and 316L may vary in concentrations of alloying elements such as chromium, nickel, molybdenum, copper, sulfur, etc., resulting in no two heats of 304 or 316 being exactly alike. Variations in alloying elements could dramatically affect the weld bead appearance and depth of weld penetration of two samples of 316L stainless steel tubing, both with a 1-in. outer diameter (OD) and wall thickness of 0.083 in., but neither having the same heats as a result of varied alloy concentration.

An unusually wide weld bead relative to the depth of penetration characterizes heats that are low in sulfur content. The large weld pool can be difficult to control and sensitive to gravity. As a result, the weld could become concave on the outside of the tube and lack repeatability. Several irregularities have been observed in the weld bead when sulfur concentrations are above 0.024%. If orbital tube welding is to be employed, it is recommended that sulfur content not vary by more than 0.010% between tubes being welded together.

Then there is the issue of hwat type of shielding/purging gases to use...

Shielding/Purge gas. Shielding gas can be a critical ingredient in the success of a weld. Shielding gas minimizes porosity in a weld and can, in some cases such as mixed gases, almost eliminate porosity. Also, shielding gas is used to purge possible contaminants from a weld area, and manipulation of purge pressure can be used to support a weld while it is molten. For the sake of economy and simplicity, most welds are developed using only argon for shielding and purging. However, some of the more difficult applications necessitate the use of mixed welding gases to achieve the weld quality and results demanded by the X-34's high-pressure applications.

Mixed gases were used for both shielding and purging. Although mixed welding gases have their problems, the benefits allowed the X-34 program to weld difficult - but necessary- applications that would have otherwise forced program costs up and vehicle delivery schedules to slip. Specific benefits of the mixed welding gases include setup of a reducing atmosphere that effectively eliminates moisture from the welds, resulting in little or no porosity; consumption (burning) of the hydrogen component of the gas mixture during welding, which effectively adds heat energy to the weld; heavier wall tubing that can be welded with less amperage; and a more focused weld, with better direct penetration.

Shielding gas was critical in solving problems when welding difficult applications of very heavy wall tubing/fittings with dissimilar chemistries (i.e., different sulfur contents) and in addressing severe pool shift, but its use created other problems related to mixed purge gases in K-bottles and the obtaining of a consistent mixture ratio during purging. For instance, if the bottles yielded a slightly higher hydrogen ratio during welding, the weld would be hotter than expected and the subsequent weld probably would not meet inspection criteria. Therefore, consistent mixture-ratio delivery became a critical factor that had to be controlled.

The gas supplier suggested that, when using a gas mixture of argon and hydrogen, a K-bottle with a siphon tube that stirs the gas mixture as it siphons through the tube should be used. This would help prevent gas mixture stratification. Another vendor recommended using a lamp on one end of the K-bottle to mildly heat it, creating a convective heat flow inside the bottle to stir the gas mixture.

Orbital Science specified gases to have less than 10 ppm of oxygen and 3 ppm of moisture to minimize porosity in the final weld. The X-34 program required the following welding purge gases: 100% argon, 95/5 (95% argon/5% hydrogen), and 92/8 (92% argon/8% hydrogen). The reason 95/5 was chosen was because it is a standard mix and a reasonable starting point. Another particularly difficult application required further weld development, which deter- mined the need for a 92/8 mixture. Once the desired results were obtained, the application was discontinued, but it is believed further potential exists in higher hydrogen mixtures. Practical limits of this approach are in the 12 to 15% hydrogen range. Here's the complete article:

http://www.aws.org/w/a/wj/2001/03/0039/index.html

Finally there's the potential issue of electrodes...

Electrodes. Electrode geometry has always been an important orbital welding parameter because it has such a pronounced effect on weld shape and penetration. The use of properly prepared tungsten helps ensure repeatable welds. The typical geometry is a 22-deg taper with a 0.010 to 0.020 flat tip. A tip without a flat point may create an unstable arc and produce welds that wander from side to side. A flat point allows the arc to come off an edge, thus producing a stable arc. The flat point also has the other advantage of extended tungsten life and, most important, a tungsten-to-work distance not compromised by having a sharp-pointed tungsten tip break or wear back.

The X-34 weld schedules were relatively insensitive to changes in electrode geometry between a wide breadth of weld schedules. The majority of the electrodes have a 20-deg taper with a 0.010- to 0.015-in. flat tip. Electrode material did matter in some cases, depending on joint size (i.e., tube OD, wall thickness, weld head, purge gas, etc.). The program migrated from thoriated to both ceriated and lanthiated tungsten electrodes, which is consistent with what is used in Europe and Japan. Health hazards associated with grinding thoriated tungsten are behind the move to ceriated and lanthiated tungsten. More than half the applications favored ceriated tungsten, and lanthiated worked well when using mixed purge gases.

Now if all of this is accounted for, then the only possibility for problems may originate from this...

Tube preparation. As in all welding, fitup is critical to successfully producing repeatable welds. It is especially critical with orbital welding because specific parameters such as travel speed, welding amperes and arc volts are preset. Any high-low condition or tube ovality problems will have an adverse effect on weld quality. The tubing used for square butt joints must be cut square and the end face machined perpendicular to the tube centerline using a facing tool. A tight butt joint is a critical factor in fitup.

Beveling, or chamfering, the tube ends was not desirable. Material removed by chamfering could result in additional weld joint concavity and cause the wall of the weld joint to thin. All X-34 tubing butt joints used only the base material being welded.

So, in summary, orbital welding involves much more of a focus on many different factors in which all are critical to the successful and consistent production of desirable weld deposits required for high purity and ultra high purity applications, and none of these factors can be taken lightly, or dismissed even more so than in less critical applications... So please re-read the links I posted previously. Like I mentioned before... if you are all still asking questions then you didn't take the time necessary to learn all of the possible causes because there are certainly more than one listed in the article I posted in my previous post. get off your butts and start reading!!! :) :) ;)

Respectfully,
Henry

Topic INHERENT RECTIFICATION OF THE ELECTRIC OUTPUT By Stephan Date 09-06-2009 15:09

Hamid,

thanks for these additional descriptions.

Quote: "...and i think have enough information regarding TIG welding procedure..."

and

Quote: "...(b) isn't my answer its the answer of examiner. I don't know about its correctness..."

Hmmm... this again sounds a bit strange to me - forgive me the honesty - as it sounds a bit... contradictory?

Anyway, according to the nowadays valid theories the tungsten electrode must have positive polarity, i.e. act as the anode, to emit 'massive' ions. These again, to keep it very short, are accelerated across the column, impinge on the aluminium surface, or the Al-oxide surface layer respectively, to hereby enable a relatively 'stable' GTAW process behaviour.

Thus, in general and basically, DC+ would be thoroughly feasible to be used for GTAW of aluminium and its alloys. However, anode overheating effects are the result what's the reason again that this technique is just very rarely used. Amongst others, to avoid tungsten inclusions caused by molten off electrode material. Nonetheless, it is - from the theoretical and also practical standpoint definitely possible.

In this context by the way. No, I don't "...want to say that real answer is DC with straight polarity. (d)

Anyway, the 'regular' way of GTAW aluminium and its alloys is to use Alternating Current. Hereby, simply put, the electrode material is allowed to 'cool down' during the period of acting as the negative polarity cathode, and to be protected hereby from a deterioration due to superheating.

But... physically governing the GTAW process is as well-known the 'thermionic' emission. The stability of a thermionic emission again depends on the cathode temperature, i.e. in case of electrode polarity is negative, its temperature is determining the 'amount' of electrons emitted towards the plasma, simply put. Another crucial point besides the cathode temperature with GTAW, is the work function of the electrode material. Amongst others that's the reason for doping the pure tungsten with rare earth metal oxides like La2O3,...,.

For a general simplification, let us agree that the cathode temperature is very important for the arc plasma stability and thus, for the welding process stability itself. And let us just keep in mind, that the electrode work function is depending on the cathode temperature as well.

So far so good. What happens now when AC GTAW? Well, of course we are using variable polarity depending on a specific frequency. Once the tungsten electrode has positive polarity (anode) emitting ions to be impinged on the surface layer on the one hand. Being the anode however, it is bombarded by a high amount of low mass but highly accelerated electrons and thus being superheated. And once the electrode has negative polarity (cathode) emitting electrons to be accelerated across the column and to swap their kinetic energy into thermal energy - i.e. to melt the parent material, but to be otherwise allowed to 'cool down' during this period.

Coming slowly to the point...

As the polarity changes one can observe an inherent thermionic behaviour during a very particular period – which is as the current drops to 'cross' and rising again to 'leave' the normal current zero line. Here the thermionic behaviour of both tungsten electrode and base material does change as well. In other words, as the electrode is anode – i.e. having high temperature improving the emissivity for ions – the emissivity for electrons of the ‘colder’ aluminium weld pool does deteriorate. This again leads to a waveform imbalance which is referred to as ‘Inherent Rectification’.

There is, mentioned by the way, another phenomenon with AC GTAW of aluminium and its alloys, referred to as ‘Partial Rectification’. But due to this was not the issue of your original post, I don’t want to deal with this herein.

I am honest with you, I have never heard of the term ‘suppressor’ before. But however, to overcome the ‘Inherent Rectification’ phenomenon there are – to the best of my knowledge and as far as I was allowed to learn – different ways:

1. Use of series resistance = inefficient means

2. Parallel bias voltage = relatively costly and complicated

3. Battery series capacitance = often used to overcome inherent rectification

4. HF- superimposition to stabilise the ‘normal current zero line’ behaviour

5. Use of pure rectangular wave form power supplies enabling the current to cross the normal current zero line rather ‘instantaneously’

There may be others, being unknown to me. Therefore it will be interesting to know what the real GTAW experts say –> Lawrence - Henry ?

I just can assume that a ‘suppressor’ might be a series capacitance suppressing the arc instabilities through ‘rectification’ phenomena by stabilising the arc behaviour in AC GTAW.

Hope this helps a bit.

Stephan

Topic tungsten selection By Superflux Date 05-27-2009 15:48

Was recently involve on a peroxide system with no tolerance spec..., zero tungsten inclusion. One thing I found was after the electrodes were contaminated (ie. dipped in the molten puddle), rather than simply re-preping the point and leaving all the stainless steel soaked into the tungsten, break off the blob prior to regrinding and as fredspoppy mentioned polish and flatten the point.

Topic tungsten selection By Fredspoppy Date 05-27-2009 12:46

A bit more info may help. Are you doing manual GTAW? Preparation of the tungsten is the most important item. The taper should be ground in the long direction and the end should be ground with a flat. Grinding marks around the tungsten will cause stress risers and without a flat, the current density at the point can be extremely high, causing the end to pop off. Back in my days as a welder in the Navy nuclear program, all tungsten grinding was done, for the welders, by the tool shop. The tungstens were polished to a very fine finish and inspected with fluorescent PT to insure no surface defects.

Inclusions caused by the welder dipping the tungsten into the molten pool are a matter of technique. The type of tungsten has little to do with the problem. Proper end prep and a adequate diameter for the amperage level being used will go a long way to helping eliminate the problem. Good luck.

Topic tungsten selection By Lawrence Date 05-27-2009 12:37

Mick,

You really diddn't tell us enough about your process to provide solid answers.

But my gut says that the electrodes are not the problem...

Tungsten inclusions come from two main possible reasons
   1. Tungsten is overheated and small droplets transfer across the arc into the weld
   2. Welder stabbs electrode into the work.

Cerium carries as much current as thorium and lanthanum and more than zirconium or pure; So your not going to find a doping alloy that provides more capacity than cerium.

Are you working with Alternating Current and aluminum or DC and steels?   Knowing this would go a long way to providing help.

Generally speaking if you are getting enough tungsten in your inclusion to fail an RT (in most codes) you have dropped in a substantial amount... This is almost always attributable to poor operator performance...   Either an electrode diameter is selected that is not rated for the current being used. Or the electrode is simply poked into the work and the operator did not bother to stop and remove the inclusion before finishing out the weld.

Topic tungsten selection By mickdale Date 05-27-2009 06:52

we used to use thoriated tungstens but currently use ceriated.
we seem to be getting a fair amount of tungsten inclusions when radiographically testing.

can anyone suggest an alternative tungsten for GTAW that may be better?

any advice greatly appreciated
thanks
mick

Topic Attn. TIG hands- BEWARE! By boilermaker Date 01-21-2009 01:54

I can say I've used it in the boiler welding tubes, never having had a tungsten inclusion in an x-ray...I've even taken a tube test for nuclear work, with the inspector watching me put the hot pass in and starting the arc like you mentioned. Never heard it being called "busting off" though. It will help keep tungsten cleaner!

Topic Need Some Advise!!! By pipewelder_1999 Date 12-30-2008 19:20

I made the jump from welding on submarine piping systems to boilers and pressure vessels. The amount of documentation and control changed considerably. I will admit that some of it was a relief as I thought having to take a welding test every 30 days was an extreme reading of "... minimum requirement for .... " that some commands took advantage of.

When I got out of the Navy

I was amazed that 1200 PSI boiler tubes didn't even require a visual by a "certified" inspector or RT or something.
I sw where undercut was ALLLOWED as long as it wasn't too deep.
I saw lifting lugs welded onto boiler waterwall panels WITHOUT NDE.
Welders could weld "Forever" as long as they used the process.

On the other side I saw

3/4" sch 80 pipes open to the atmosphere with 1 1/2 pages of procedure for welding in on a steam trap manifold.

I saw welders have their monthly quals rejected for tungsten inclusions that measured 1/64" of an inch. Just becuse it was tungsten. It was well below the allowable indication size and was rounded.

I have seen people threatened with reduction in pay to the next lower paygrade and 1/2 mos pay for two mos for welding something with the correct material without getting the typo corrected in the work procedure prior to doing it. The boat left before the typo was corrected and routed yet the person still was written up. Had the type been corrected prior to getting underway it would have been late. No punishment for the procedure writer that didn't know the difference between RN 60 and RN67.

The specifications for industries vary. Everything should be written somewhere. A welding inspector is of little value without specifications and acceptance criteria. The advantage of sticking to "What the code says" is always knowing where you stand. I know someone in the past that left a decent paying job 2 minutes from his front door over flame straightening duplex. If you talk to him today, he has no regrets nor a full time job.

Getting a clear understanding of what y our employer wants is highly advised. If the person you work for has different "inspection ethics" than you it can be a difficult position. Engineering departments may not understand the pressure you are under to decide if something is "acceptable" and maybe talking with them can help provide some acceptance criteria for things. Also look in your comnpanies quality manual. See what the policies are. What the organizational structure is supposed to be etc.

Thos are just opinions basedd on very limited experience and may not be suitable for all situations. :)

Topic Non-metal surface inclusions By CWI555 Date 11-06-2008 14:21

AWS 3.0 2001

"Inclusion: Entrapped foreign solid material, such as slag, flux, tungsten or oxide."

In your case, it could be an inpurity in the base metal/filler or an oxide whichever is applicable.

Topic Attn. TIG hands- BEWARE! By Superflux Date 09-20-2008 06:26

Cruising this forum, I've noticed a lot of people claiming to be "run off" by QC... Whom ever these inspectors are working for must have the ultimate Dental Plan with 100% E.R. coverage. And where do CWIs have such authority? The only time I've ever been directly involved with "gettin someone's money" was when they failed the test. Their stencil can show up for the 3 strikes (failed X-rays) and your out (of a job) but to just walk up and fire a welder...that's always been the Foreman and other supervisor types to do that dirty work.
An interesting twist on the Tonguestone inclusion issue though. Current project, hydrogen peroxide system has a zero tolerance for tungsten inclusions. Strange how a metal with, like 6,000F melting point can be eaten up by something Grandma made us gargle our throats with before beddy-bye time.

Topic Attn. TIG hands- BEWARE! By pmedicann Date 08-06-2008 21:16

Devil's advocate...just for arguments sake! Can you guys handle that and not call me a pencil pushing, book smart, never welded a lick IDIOT!

Might the reality of the situation be he was run off for how he handled the situation when it was brought to his attention vs. the actual practice. Seems to me, from the information provided in this post, it would NOT have been too tough to invalidate the inspectors critiques given an understanding of codes and procedures. As far as that is concerned, it sounds like invalidation is exactly what happened with the offer of his job back. Did the welder have enough knowledge to call the CWI's BS?

Where was the welder's supervisor, union rep, or company man to come to his defense with a knowledge of CWI work?

There are a lot of welders out there who want to leave the "book stuff" to others so they can just weld. In the end, who is really losing with that viewpoint? We have been led to believe this guy got run off his job for his technique, when in reality, it MAY have been for his lack of knowledge when it comes to procedures and codes. Had he had the knowledge to begin questioning the CWI for proof of his claims of tungsten inclusions, he might not have had to go anywhere. It sounds like some of you guys in this post have this knowledge that maybe this other guy did not. From the way you speak, I have a case of beer that says you wouldn't have had to go anywhere (of course most welders are bastards that would walk just to get the case of beer!) You wouldn't have had to go anywhere because you knew to ask for documentation of tungsten inclusions or code specifics outlawing the busting off technique. Has anybody taught welders how to handle these situations in a professional, documentable manner?

Topic Attn. TIG hands- BEWARE! By spgtti Date 07-19-2008 22:00

Generally when striking an arc off the wire you hit the side of the tungsten which in turn preserves the sharpened end. In any case the only time the QC should have become involved was after the shots had come back with inclusions unless there was something written in the procedure regarding arc initiation. Technique should be up to the welder if not written into procedure.

Topic Attn. TIG hands- BEWARE! By aevald Date 07-19-2008 03:50

Hello spgtti, I can only guess that this particular inspector felt that by striking the tungsten and starting the arc between the base metal and the end of the tungsten with the rod that there would be transfer of the rod to the tungsten point or visa versa. So possibly in his eyes he felt that there would be an inclusion of the tungsten into the weld metal. Certainly plenty of room for interpretation and verification. When one is considering the arc starting methods that are available, high-frequency start will provide the best possibility of no tungsten transfer, lift-arc start will provide none or minimal inclusion due to the lower amperage start feature and operator ability, and finally the scratch-start method could possibly yield the most inclusion if "improperly done". Here again, I believe operator ability, code requirements, and possibly verification through testing should be the determining factors to judge this by. I wonder what this inspector expected in the way of starting the arc? or if this question was asked of him? My $.02 additional cents. Best regards, aevald

Topic Attn. TIG hands- BEWARE! By spgtti Date 07-19-2008 03:20

Unless I'm deep down in a groove or the machine has a lift arc, this is how I fire off a torch. I hadn't ever had any problems from QC when striking an arc this way. I think it keeps your tungsten sharp longer and prevents leaving tungsten inclusions. I'd love to hear that inspectors reasoning for running someone off over that.

Topic Attn. TIG hands- BEWARE! By aevald Date 07-18-2008 22:32

Hello 3.1 Inspector, in the earlier years of field type GTAW welding either a scratch start type method was done by contacting the tungsten to the work to initiate the arc or the use of the filler wire to initiate the arc between the tungsten and the work was used or possibly the use of a copper scratch block off to the side of the joint to initiate the arc and once started the arc was brought into position in the groove and then filler was added or the arc was brought to the filler as it may have already been positioned in the groove. Many machines used today in a lot of indoor applications now either utilize a lift-arc arc starting process or a high-frequency type start. There are however, many applications for the old-school type of method and it is still widely used in many industries. I would venture to say that the applicable codes would dictate how much tolerance of tungsten transfer inclusions would be allowed. Just a few cents to consider for this conversation. As to the high-frequency portion of this, many situations prohibit the use of high-frequency due to damage to sensitive electrical equipment or other considerations where the high-frequency could cause issues. In many of these cases either the lift-arc form of arc ignition(my understanding of this option on some machines is that it allows the arc to fire after the tungsten is lifted due to being able to isolate the zero voltage crossover point in the supply current, thus it doesn't use high-frequency) the scratch-start form of arc ignition would be the only reasonable choices. Best regards, aevald

Topic coating on mild steel tig wire By aevald Date 06-11-2008 21:44

Hello again Kix, since I don't know the exact make-up of the "copper colored coating" that is applied to the various ER70S2,3,6 designations and whether this "coating" will float out, vaporize in the arc, combine in the form of some sort of metallurgical dilution of the base materials or possibly result in an inclusion of some sort I really can't say why these folks were removing it before proceeding with their welds. I do seem to recall additionally that in some cases they were using copper scratch blocks to fire the arc off on and then dragging it into the groove to make the welds so as to avoid tungsten contamination. This was before the days of lift-arc power sources and small portable inverters. Just a little more to ponder. Regards, Allan

Topic argon purity By aerowelder Date 05-24-2008 21:24

Lawrence,
I have welded a new part and have had it x-rayed. I only had one defect and that was a .050" tungsten inclusion. I believe that was because I first tried 3/32" and quickly realized that that was too small of a diameter. I did have a few pores of porosity but they were well within acceptable limits. Nothing like what I was getting before. Thank you for the handy tips. I was thinking contaminated gas but it was just my incorrect settings. I have learned something new today. I hope to use this information in the future.

Topic x By CWI555 Date 04-04-2008 19:50

API 1104 will cover about anything the engineer wishes. Under materials it states API 5L or ASTM standards. Under fillers, an exclusion is given for using something other than the c/las.
If your working on a compressor station upgrade, it is exceptionally unlikely you'll be working with B31.1. I would suggest utilizing the search function of this forum for post related to the ASME pressure pipe series in particular B31.3.

As for tungsten inclusions, you'll have to pick a code to get an answer as to whats acceptable. From your description, That code could be B31.8 transmission lines, B31.3 process piping, or 1104, or something entirely different. Project specs should spell out what code your working to. Do you not have a procedure? and if not, why don't you have a copy of the relevant code? are you the owners inspector? or are you the examiner?

As for "what point do they become a defect", depends on size usually, and they normally found in the radiograph rather than the visual. though possible, I'd be a bit more than disturbed if a welder left a rejectable chunk of tungsten on the surface of the weld.

Regards,
Gerald

Topic x By thirdeye Date 04-03-2008 03:03

Hi Paul,

Welcome to the neighborhood. Doing some "homework" and finding answers is always a good idea before getting on the job, this applies for new inspectors and old ones alike. For questions, you have come to the right place as there is a huge base of knowledge to tap into here. I read your (first) post yesterday and assumed you mis-typed IT for TI and that you were referring to tungsten inclusion, especially after your reference to SS piping. Is that the case?

Heck, I was expecting to see a lively discussion tonight on whether a TI would be considered a "nonmetallic" solid ...... or not.

~thirdeye~

Topic x By CWI555 Date 04-02-2008 22:51

Paul,

I am with Al on this one. You've mentioned api 1104, so I'll go with the 20th edition

12.8 INSPECTION AND TESTING OF
PRODUCTION WELDS
Production welds shall be inspected and tested in accordance
with Section 8.

8.2 METHODS OF INSPECTION
Nondestructive testing may consist of radiographic inspection
or another method specified by the company. The method
used shall produce indications of imperfections that can be
accurately interpreted and evaluated. The welds shall be evaluated
on the basis of either Section 9 or, at the company's
option, Appendix A.

9 Acceptance Standards for
Nondestructive Testing
9.1 GENERAL
The acceptance standards presented in this section apply to
imperfections located by radiographic, magnetic particle, liquid
penetrant, and ultrasonic test methods. They may also be
applied to visual inspection. Nondestructive testing shall not
be used to select welds that are subjected to destructive testing
in accordance with 6.5.

1104 uses a lot of acronyms for indications, remember that any can be used for visual testing as applicable in accordance with para 9.1:
Radiography;
IP   inadequate penetration
IPD inadequate penetration due to high low
ICP inadequate cross penetration
IF   incomplete fusion
IFD incomplete fusion due to cold lap
IC   internal concavity
BU burn through
ESI elongated slag inclusion
ISI isolated slag inclusion
P porosity
CP cluster porosity
HB hollow bead porosity
C   cracks
EU cover pass undercut
IU root pass undercut
AI accumulated imperfections "All but IPD and undercutting"

Most terms are under radiography with the following exceptions;
UT method
LS linear surface
LB linear buried
T   transverse (other than cracks)
VC volumetric cluster
VI volumetric individual
VR volumetric root
AR accumulated relevant indications, "modified to be inclusive of all UT indications as compared to AI for RT

Having quoted and stated the above, no combination of any of the above comes up with "IT" from 1104. If I were dyslexic, I'd be taking IT to mean TI or tungsten inclusion. Since you mentioned stainless, it may be the case that, that's what your thinking. I looked at all the terms in appendix A as well, and posted them to myself in a private message in the off chance this forum format converted a copy paste to "IT", no dice on that one either.
Al's advice is sound, It would be a very good idea to get the terms down before you write a report "rejected for IT". /edit point will be made without previous statement.

Respectfully,
Gerald

Topic Farm Code FC-2002 By Tommyjoking Date 12-06-2007 09:39

If you happen to dip your tungsten during any gtaw weld..just continue on...coating the tungsten with the parent or filler metal will prevent any tungsten from hitchhiking on the arc and causing an inclusion. When presented with an xray showing any type of porosity simply hold the film up to a light source and get a disgusted look on your face..then wipe the film on your sleeve and take another quick look...hand it back to the inspector and with as much disdain as you can muster tell him to go "learn something before you come back".

aluminum is aluminum! Any Al filler will do the job ...jeez its not like its made of steel....cut strips off the parent metal or use pop tops for filler or any rod will do as long as it sticks it together.

Hastelloy is just a bastardized inconel which is a stepchild of stainless so any stainless rod will do the job and get you out of there.

Topic CIT - ever heard of this? By CWI555 Date 12-05-2007 17:23

"the reason for the higher sensitivity over all compared with AUT. "

Stephan.. I would be very interested in reading the gentlemen's explanation in detail in regards to how how he figures CR is more sensitive than AUT. Especially for PAUT. (phased array automated UT)

There is a contingent of old school NDE types out there that are dead set on regaining RT dominance. However; that horse is out of the gate long ago never to return.
RT has come a very long way compared to old school methods, but it has some specific limitations.

I've had the good fortune to take part in some trials between phased array and CR. The result of which left me with a less than comfortable feeling in regards to RT.

Having said that, I see both staying around but RT in a limited role. The cost of doing both on a given project usually is the limiting factor, however; if you had a super critical
project, that would be your best method.

RT's primary limitation is in it's ability to pick up planar flaws. (cracks, lack of fusion)
UT's primary limitation is in it's ability to pick up volumous flaws. (slag, porosity, Tungsten inclusions etc)

Using porosity as an example for comparison: A pore will have a specific volume of missing material, this is an ideal flaw type for RT
Whereas a pore is typically at least a partial or wholey ominidirectional reflector in regards to UT. For UT the energy impinges on the pore and is reflected back to it's point of origin by only a small portion of the flaw as the rest is either refracted, diffracted, mode converted, or otherwise sent away from the receptor.
It should be noted that AUT can pick up on those otherwise lost waves and waveforms and be reasonably assessed due to using multiple channels/transducers/elements and the ability to tie those together in a coherent imaging process. (such as an Sectorial scan for PAUT, or phased array)

Using a planar defect such as a lack of fusion for comparison: This is the ideal flaw type for UT.
Where a planar is typically very tight in regards to it's width leaving a very small volume of actual missing material, which leaves very little change in material for the RT to pick up on. Even in that, the volume missing can be missed all together by RT depending on the flaw orientation, whereas UT, phased array in particular would be ideal to find this flaw type, as the angle of incidence can be dialed in and in the case of phased array, ranged in.

As for presentation, Old school UT was A scan (time distance trace), B scan was a side view cross section, and C scan was a top down view cross section. The current state of UT presentation is only limited by computer processing speed, which in todays world is several orders faster than when I began in the 80's.

Another factor involved would be the security and safety. This is the achilles heel of radiography. No matter what methods of presentations, accuracy, etc that you can come up with, it still requires a source of radiation. Unlike the world of yesterday when people weren't flying planes into buildings, today the risk benifit must be evaluated in regards to keeping these sources around. The more security the various nations of the world, the IAEA, and other authorities impose upon companies utilizing radiographic sources, the more expensive it will be to perform. Economics alone will start and has started in a lot of places, the move to something that does not require the sources.
I believe it will be this factor that ensures the dominance of UT as it can do all the above, but without the ionizing source.

Regards,
Gerald

Topic Purge Chamber By jd369 Date 09-14-2007 18:43

Just thought I'd show a few pics of the purge chamber I built as a test rig to prove out a welding process for a customer. The actual part will be welded in another much larger version of this that suits the part. It's for an aerospace application of welding 6/4 titanium. I have it set up with an automatic wire feed with a foot activated switch. I can purge the chamber down to 0.01% oxygen in about ten minutes without the use of vacuum. I also use compressed argon to run my pencil grinder encase of tungsten inclusions.
There is a copper tube all around the perimeter with 0.045" holes drilled every 1/2" to allow a good uniform purge of the chamber. The one way valve to purge the unit is built in below the perf plate that can be seen in the one shot. The wire feed unit seals as it is screwed into the chamber (old mig whip). The gloves are rubberized sandblast gloves. They are held on with a large industrial rubber band and then we tape them to ensure they cannot be pulled off during use. We use a oxygen sensor to determine the oxygen content prior to welding. This particular model will be good for our future application as it has a long stainless "snout" that can be pushed down into long tubes atc, to ensure all entrapped air has been removed from the drop thru side of the weld prior to welding.
We like it much better then the flexible bags, they are a real pain to work in, kind of like sticking your hands into a marshmellow and trying to weld.
I'll try to add the pics now.
Regards
Jim
P.s. I'll get some shots of test pieces as they come out in the as welded condition.

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Topic ut /rt misdirection By g32141 Date 08-21-2007 22:51

I have seen this lots of times. Either the weld repair was mismarked or the repair welder took it upon himself to remark where the repair in his opinion should be.

With UT the indications should be marked up rather precisely.

What was the seam that you fixed? What code was it?

Unless your calibration block for UT is made from the same job material you can expect some depth and or distance variations.

Please explain "a fairly complex inclusion". Slag, copper, tungsten?

The more details that you can give us the more we can help you sort it out.

You also need to shake the since I didn't see anything I'll filler up attitude because that won't fix a defect.

Topic 2% thoriated...radioactive? By 803056 Date 08-19-2007 11:24

The tungsten electrodes doped with thorium oxide are an emitter of alpha particles. They are large, slow moving radioactive particles that pose little risk if some very basic work practices are observed:
1) Use a grinder that captures the grinding dust from the tungsten sharpener (I know everyone has a wheel dedicated to just sharpening tungsten!)
2) When disposing the grinding grit, use some care to prevent the material from becoming air-born.
3) Wear gloves when sharpening tungsten and wash your hands afterwards (at least wash your hands as minimum precaution).
4) Wash your hands before eating any food to make sure any tungsten particles have been removed from your hands.
5) Likewise, if you smoke, wash your hands after handling the tungsten and before you handle the cigarette.
6) Avoid inhaling the dust from sharpening tungsten.

These words of advice came from a pulmonary doctor that is member of a craft committee I work with at a local Vo-Tech. Dr. Alexander Peck says that as bad as the thoriated tungsten is, the cigarettes will get you first if you are a smoker. The alpha particle can be stopped by paper, glass, your work glove, and yes, your skin. The danger comes from how the alpha particles interact with the soft linings of the gastrointestinal tract and your lungs. They can initiate abnormities in the tissue and can result in cancer.

There is little to no danger from grinding the welds unless you have tungsten inclusions (no one has problems with tungsten inclusions, right?)

Stephan, I have heard that some European countries handle the grinding grit from sharpening thoriated tungsten and stub ends as low-level radiation waste. All waste materials (from the thoriated tungsten) must be returned to the vendor for proper disposal. Do you have any insight on the matter?

Anyone new to the forum should know that Stephan is a resident welding/science guru. His words of wisdom are on the spot.

Lawrence, I followed your link back to 2001, some very interesting information!

Best regards - Al

Topic Grinding or sanding Aluminum By Lawrence Date 05-22-2007 19:03

If I was routing cracks in a massive aluminum casting and used parafin on ball burrs, I often would also have access to a hot vapor degreaser which would float away any residual parafin or dye penetrant.

I think for the most part that the tools are rotating at such speeds that everything is ejected including parafin.

On more open surfaces I would simply use a clean 80/120 grit disc to remove any residual.

Lots of X-rays on these projects, Rejects if any were always due to tungsten inclusions or insufficient crack removal. 100% of cracks must be removed prior to welding aluminum or magnesium (best to verify with FPI), Ya just won't have much succsess if you try to weld over a flaw or "burn it out"

Topic Edge prep on 6al-4v for x-ray By Lawrence Date 04-17-2007 05:17

0.032 titanium test coupons either sheared or watercut should not need to be filed anyhow. If you must file use a dedicated tool, however I advise against.

I suggest a 1 1/2" 120 grit silicon carbide disc driven by a pnumatic die grinder with rear exhaust @12,000 rpm for pre weld oxide removal and surface prep followed by isopropal or acetone... NO TRICHLOR for Titanium.

0.032 needs no root gap. The coupons should be a 100% perfect flush fit with absolutely no mismatch and restrained in in a backpurge fixture.

The filler wire (as Al mentioned) should also be cleaned with acetone right before welding and always kept under the argon shield for 100% of your arc on time... If you must restart, clip the end.

Just about the only way to get tungsten inclusions with 0.032 6Al4V is to stick the tungsten.... The only exception would be if you have one of those Lincoln Invertecs with the recalled reverse polarity pulse sequence at arc start. I suspect your "tungsten inclusions" are in reality debris imported by the file.

0.040 or 0.063 dia. tungstens will do. A diamond wheel is best but at least have a look at your typical tip prep under at least 10X to be sure your not bringing any uninvited guests to the party at the end of your electrode. If no diamond wheel I like a 2 inch 120 grit belt sander worn flat to put on a nice smooth finish.

Acetone or Isopropal Alcohol leave less residue and evaporate quicker than MEK

Topic Edge prep on 6al-4v for x-ray By jwm80 Date 04-17-2007 01:09

We've been getting alot of rejections mainly due to porosity and tungsten inclusions, even though we normally don't stick our tungstens. My boss seems to think that prepping the edges with a file is a good way to clean them. I don't think I agree with him.

The thickness is .032, full penetration groove weld. The parts go through a chemical cleaning process prior to us recieving them. Any help will be appreciated, and maybe links if you have any.

Thanks in advance.

Topic Pedal pumping when GTAW Al tubing. By bozaktwo1 Date 03-02-2007 12:51

I have done a lot of aluminum GTAW over the last 20 years, and there are always 3 constants: use only pure (green) tungsten, clean argon gas, and a clean stainless steel wire brush before every pass. I like to burn each pass in hot and fast, especially if I'm purging the backside. If you're purging, make sure you keep the pressure in the required range on your wps. Because pure tungsten is so brittle, if you dip it, you probably have left an inclusion, and it needs to be ground out. I have learned to always start with a clean electrode...for your .065" wall thickness, I might use 3/32" and grind a slight crown onto the end, then "run it in" on a piece of clean, wire-brushed scrap. This makes a very clean, rounded end on the electrode for excellent control. The "stubbly" appearance of your bead surface may be due to poor gas quality, not enough gas, too much gas, or the wrong kind of gas. Pure, oil-free argon works best, in my opinion. If you are having trouble keeping your arc steady, try increasing the amperage and learn to feather the footpedal to maintain it. You don't want to allow the puddle to solidify, as this can cause cracking and lack of fusion at the toes. As for not getting burned on the job, try using an old glove or a scrap of leather or glass cloth, wrap it completely around the tubing and secure it with a few strips of heat tape all the way around it, just tight enough that you can rotate the entire thing around the OD of the tube. That way you can hold the thing like a bike handlebar and pull your wrist without changing your angle. Once you have that down, you can easily master walking the cup over 180 degrees or more of the tube in one pass.

Topic heli arc By - Date 01-17-2006 20:50

One last thing...Using helium as the shielding gas, it tends to wear down the tungsten causing the possibility of tungsten inclusions. Be careful..

Topic gas for stainless??? By - Date 09-25-2005 17:26

Nitrogen is fine for a backpurge on SS, but one needs to realize that when doing a root pass using the TIG process, the pure nitrogen will cause possible breakdown of the tungsten causing very likely tungsten inclusions. 100% nitrogen is also not recommended as a back purge for the Duplex SS. Nitrogen, being a strong austenite former, will lower the ferrite levels to possible unsatisfactory levels. It's just hard to beat good ole argon for a backpurge for SS, even the Duplex grades.

Chuck

Topic TIG WELDING 304 STAINLESS By - Date 09-23-2005 16:09

A gas lens collet body provides a number of benefits for all but the most basic of applications. The primary benefit is improved shield gas coverage. This is achieved by flowing the shield gas past a series of concentric, layered screens of varying mesh. These screens generate a laminar gas flow which optimizes the weld zone coverage and eliminates the turbulence created by a standard collet body which can draw in contaminants from the surrounding air. A gas lens collet body is almost mandatory for TIG welding oxidizing materials such as aluminum.

A secondary benefit of this improved shield gas coverage is that the tungsten electrode can be extended beyond the end of the gas cup by as much as 1 inch (2.54 cm). This electrode extension greatly improves welder visibility and can reduce tungsten inclusions and weld defects.

Topic gas for stainless??? By - Date 09-20-2005 12:32

Nitrogen above 3% can have adverse effects on the tungsten causing possible tungsten inclusions.

Topic Welding Dupex 2205 GTAW By - Date 09-06-2005 12:27

If the 6mm thickness passed and the 14mm did not, it is apparent you deviated from something. Weight loss can come from a couple of things. First of all, both the base metal and the consumables must be absolutely clean. Each pass must be cleaned after welding to remove the chromium depleted oxide layer to insure no weight loss is possible due to the oxide layer. I don't know what your purge gas is, but a nitrogen content of more that 3% can lead to breakdown of your tungsten and leave undetectable tungsten inclusions. ASTM A923 should be an easily achievable test if all is clean and the purge gas is acceptable. Without knowing everything you did, it is near impossible to figure why you passed one and failed the other.

Topic Nitrogen Purging By - Date 07-31-2005 12:52

Nitrogen will affect tacks just as it would any other part of the weld. In the TIG process, the argon purge will negate the arc characteristics upon start where that should not be a problem. The main problem with a nitrogen purge is the breaking off of the tungsten, thus causing the real possibility of tungsten inclusions. That, and the depletion of some of the austenite in the weld pool.

Chuck

Topic socket weld gaps before welding dmw's By - Date 05-02-2005 03:24

I will try to be as unprejudicial as possible in my answer as to not offend anyone. We have already discussed that maintaining an appropriate interpass temperature is vital for the welding of stainless steel. But, equally important is the amount of time it takes to get to that temperature. With the austenitic grades of stainless, chromium carbides can precipitate on the grain boundaries of the steel if maintained in the range of 800-1500F. for any amount of time. This is known as sensitization. Once you get down to the sensitizitation range, your phase balance has pretty much done all it's going to do. So, it is desirable to get through the sigma and sensitization phases as rapidly as possible within reason.
"Forced" cooling, or "accelerated cooling" is a term that can mean different methods. In a paper once written, and I can share that with you, the 3 most important things to consider when welding stainless steels are 1) cleanliness, 2) cleanliness, and 3) cleanliness. When welding stainless steel, all else is irrelevant if you do not start out clean. If the shop air is contaminated with oils from the filtration system, I don't think that is an acceptable way to cool down. In these shop air hoses, moisture can gather from the humidity in the air, dust from the activities of the every day workings of the fab shop, and oils. As you mentioned, the Wolfram can become contaminated and leave tungsten inclusions if it gets to that point. If the air is filtered and dried so as to not deposit residuals of the surface of the steel, then you are OK. Another way to speed up the process is to quench the weld with a spray mist of water. Now, that opens up another concern. Most tap water contains chlorine and calcium, neither of which is good for the stainless. It is not always practical to use deionized water, but al least you are keeping the chlorine and calcium off of the weld zone. Chill bars are another safe way to expediate the cooling process. I guess the most important thing to consider if forced cooling is implemented is using the method that introduces the least amount of contamination. That is probably the bottom line. I agree with all you said in your response to "mi jefe" about the cooling.
Again, it was great communicating with you, as you seem to be well versed in the welding of stainless steel.

Chuck

Topic nitrogen as a shielding gas for Tig. By - Date 03-31-2005 01:41

To just add to the discussion, that high of a nitrogen content can, and usually will, cause breakdown of the tungsten. Research has shown when using over 3% nitrogen as a shielding gas "can" cause the tungsten to break down and cause tungsten inclusions. If you are welding stainless steel, there are even more reasons not to use straight nitrogen as a shielding gas. You did not say whether you were welding stainless or carbon steel.

CM

Topic To Malcolm:1 more ? bottom of page By - Date 08-04-2004 17:31

The tungsten electrode used in TIG welding is very similar to the tungsten fillament in an incandescent light bulb. In the bulb, it carrys electrical current, heats up, and emits light. In a TIG torch, electrical current flows through the air/shielding gas between the tungsten and the work creating the arc that metals the base metal and the filler rod, if there is any. Tungsten is used because it has a very high melting point and good thermionic emission (it emits electrons easily when it gets hot).

The tungsten is considered nonconsumable. That is, it does not melt and is not intended to become part of the weld. Any part of it that does become a part of the weld is called an inclusion. This is an undesireable discontinuity in the weld metal. If an inclusion is large enough, or there are enough of them, the weld is considered rejectable. Of course, the weld would have to be subject to radiographic testing to detect them.

The term nonconsumable is somewhat misleading. The tungsten does get shorter over time. Everytime you contaminate it by dipping it into the molten weld pool you have to remove the contaminated portion and regrind it. You start off with a 7" tungsten electrode and sooner or later you have a 3" one. Beginners typically have a problem with this. Once you get the hang if it, though, a tungsten electrode can last a long time.

When welding thin metal with TIG, it may be possible to do the job without adding filler metal. You simply melt the two pieces together. When welding thicker material, some kind of groove will be required between the pieces to be joined and filler metal must be added. You hold the torch in one hand and feed filler metal in with the other hand.

MIG and TIG are different animals. TIG, at least as you will learn it in school, is a manual process. The filler metal typically comes in 3' lengths. And it is common to cut them in half to make them more manageable. The person doing the welding feeds the filler metal by hand. MIG is a semi-automatic process. The filler metal is fed in automatically. You press a trigger on a gun and it comes out at a preset rate. So, it makes sense it is on a spool.

TIG is typically used for critical applications when quality is imperative and productivity is not an issue. MIG is typically used when productivity is the important factor.

All this will start to become very clear as soon as your class starts.

Topic Tungsten Percentage in Base metal By - Date 05-21-2004 14:34

How are you determining that there are tungsten inclusions in the (you stated base material, but did you mean...) weld material? Most methods of NDT used to determine this have accept/reject criteria to use to determine whether or not it must be removed.
John Wright

Topic Plate Certification By - Date 03-14-2004 04:57

Hi SDrake!
Run a stringer bead for your root pass. I use a 1/8" dia. electrode with an ever so slight side to side motion (not really a weave but more like an inverted or upside down "C" motion) so that I get good "wetting action" (fusion) or "washing" at the toes of the weld without producing undercut at the bevels or LOF (lack of fusion) which in using E-7018 will produce slag inclusions by the toes of the root pass.

With E-7018, the flux coating is not producing anywhere near as much shielding gas as compared to other flux coatings found on SMAW electrodes so, holding your electrode closely (proper arc length) to the weld puddle or molten pool is critical in preventing porosity especially within the throat of the weld. Always keep the puddle on top of the slag and watch for the molten slag to run down the sides of the puddle and form a pattern of solidified droplets of slag on top of the axis or centerline of the weld face. If the solidified slag droplets are either to the left or the right of the centerline of the weld then, your work angle needs adjustment. A consistent pattern (size & location) of slag droplets
can tell you alot about what's underneath with respect to work & travel angles, travel speed, arc length and so can the color of the slag cover tell you whether or not you're welding with too little or too much current.
Also, use a flashlight and shine it on the toes and where the restarts are because the slag color (especially little inclusions or pieces) can fool you if your lighting is'nt adequate. If you find any slag that was left behind after wire brushing then see if you can get a hold of either a pointed tungsten or better yet, a piece of band saw blade to scrape out any slag that may be either trapped or left behind from the initial wire brushing. Remember that this slag is also very soft and the band saw blade is sharp so wrap some duct tape on one end so that you do'nt shred your gloves while you're cleaning!
Before you run your next pass and also on the next and every other pass, MAKE SURE THAT YOU CLEAN IT REALLY WELL!!! because if you do not, you'll end having discontinuities that'll total up beyond what is acceptable within the specified criteria or a defect that'll reject the coupons!!! You do not want that to happen... Be patient!!!

This is just my opinion but as an instructor, if one is just starting out with their first certification, I would'nt recommend to my students to use a triangular weave technique for the root pass when welding vertical up (3G) with E-7018.
I would instruct them to form a puddle at least three times the diameter but, not more than that of the electrode so that they can fuse or wash properly at the toes on to each joint member's bevel. Keep the center of the electrode on the centerline of the joint as much as possible.

Usually, only the more so called "experienced" students use the technique which you described and some are successful although, some are not!

Ultimately, if your toes look good, there are no slag inclusions, no LOF or porosity and your restarts are sound, you should be okay because it's normal to have a slightly convex face profile on the root pass when one is using SMAW with E-7018. Also, make sure that you have the proper root opening! I think you should be fine but, only the DE or NDE test will tell you for sure if you have to make some adjustments.
So cut the coupons and let us know how you made out! Good Luck!!!

Respectfully,
SSBN727 Run Silent... Run Deep!!!