American Welding Society Forum

Topic Stainless Steel Plate shrinkage after welding By ssbn727 Date 04-09-2013 05:19

Another good book to look @ is: "The procedure Handbook of Arc Welding from Lincoln Electric..." Look in Chapter 3.1-1 Title is: "Weldment Distortion"

This chapter covers: The reasons for distortion... How properties of metal affect distortion such as the coefficient of thermal expansion, thermal conductivity, yield strength, modulus of elasticity... And they cover the comparison of properties in these metals: Mild steel vs.Stainless steel, Mild steel vs. Aluminum andMild steel vs. High-strength steel...

The next topic is Shinkage control starting in section 3.1-4 through 3.1-7... Covering several practical ways that can be used to minimize distortion caused by shrinkage such as: Do not over weld, using intermittent welding, use as few weld passes as possible, Place welds near the neutral axis, Balance welds around the neutral axis, Use Backstep welding like Giovanni mentioned in an earlier post in this thread... Anticipate the shrinkage forces, Planning the weld sequence, Removing shrinkage forces after welding, Minimize welding time... With many corresponding figures

Then starting from section 3.1-7 through 3.1-9 the book covers: Equations for calculating shrinkage such as: Transverse weld shrinkage and Longitudinal bending along the pertinent equations included in the figures...

Examples of distortion control such as a T section, Three member column, Unsymmetrical beam, Welding sequence, Buckling and Twisting, Horizontal or Vertical web, Slender, Light Gage columns, Control of camber, Distortion correction by Flame shrinkage along with corresponding figures from section3.1-7 until 3.1-17...

Then there's Shop Techniques for distortion control and stress relief along with a check list for minimizing Distortion along with corresponding figures. Starting from section 3.1-17 until 3.1-19 There's also Prehaeting and Stress Relieving covering the when and why, The amount of preheat required, Methods of preheating, Interpass Temperatures, Preheats for Quench & tempered steels, Pointers on Preheat and Stress Relief along with corresponding figures. Everyone that works around welding should have this book @ the very least!

Respectfully,
Henry

Topic Welding Thin Magnesium on DCEP? By Lawrence Date 12-24-2011 05:42

I'm confused

If you are doing a performance qualification test, how can you pick and choose polarity and shield gas? Won't your test include a WPS that you will need to follow? Your tag says your an aerospace welder so I'll assume AWS D17.1, where I know every welder performance qualification must be done to class "A" standards, no matter what the production work might be, and that means the welder doing the test must be provided a written WPS that itself has been qualified by even more extensive testing.

Technically speaking:

A 50/50 mix of He/Ar is good for DCEP welding of magnesium... But for a groove weld I don't think it would be a good choice. The benefit of DCEP for Mag is that it provides a wide and shallow weld pool, which is not always a great thing when you are trying to make a full penetration groove weld from one side. AC on the other hand, provides a more columner arc, which in turn tends to penetrate deeply and directionally, which is a benefit when welding groove welds in sheet.

Zirconium, Cerium or Lanthanium are better than pure for DCEP.. Thorium is a really bad choice for this polarity (especially under X-ray) because DCEP puts 70% of the arc energy at the tip of the electrode and only 30% on the work.. This means that you will need a larger sized electrode and the end will still ball up.. When thorium balls up you *MUST* assume that part of your electrode is transferring across the arc and will bust an X-ray... If the tip of the "thoriated" electrode is changing shape at all while you are welding, it's a bad thing. If I were taking the test and had a choice it would be Zirconium.

The copper/brass backup/heat sink is fine #ONLY# if you leave a recessed area directly below the groove in the coupon as there absolutly must be a space left for reeforcement on the back side of the weld... A heat sink placed directly in contact with the back of the groove will freeze the puddle and make full penetration next to impossible. Also keep in mind that typically the reenforcement on the back side of a magnesium groove weld will be even larger than that of Aluminum, which is expected to be 3X of steel.

Generally purge is not required,,,, But again... This should be covered in the Welding Procedure Specification (WPS)

In my experience with DCEP Mag welding (which is considerable) it's typically used for buildups on castings, where lugs have broken off or a bore needs to be repaired. The DCEP minimizes heat input and penetration often for the purpose of minimizing distortion on highly restrained weldments, or to minimize temperature differences on highly preheated castings with complex geometries. It can only be done in the flat position as the tungsten will be too large and soft at the end for even a horizontal weld that's more than an inch or two. I would expect that a 3/32" or even larger tungsten electrode would be best for DCEP even on .062 magnesium. Water cooled water cooled water cooled torch!

I'm not sure why you are worried about the Cathodic etch or "cleaning action" anyhow. If you don't have a procedure that calls out shield gas and polarity how can the inspection criteria be so strict as to disallow any etching at the toes of the weld?

Edit: Don't worry about the black "smut" on the DCEP welds.. That is also typical and simply may be removed post weld with a stainless steel wire brush.

Topic common practices for thin-guage stainless TIG (GTAW) By Lawrence Date 07-21-2009 18:49

Pulse GTAW is not commonly used in manual welding of thin stainless (I"m sure there are exeptions and folks who may disagree) In my opinion there are a few joint types that can benefit from pulsed GTAW in production, but for the most part, pulsation for manual GTAW is just a costly option that sales folks pad their pockets with.

If burn thru is cause for rejection than argon backups and heat sink tools will be required...

But you sound like your just looking for things to practice in order to have the best skills you might possibly bring to a job.

Thin stainless fillets or thin to thick fillets are excellent practice... But in my opinion for the beginner this excercise can also be done with plain carbon steel sheet.

Controling heat input and minimizing burnthru on thin fillets is great practice no matter what the base metal.. Torch angle, wire feed technique, surface prep, electrode prep... all are very similar whether stainless or plain carbon steel... There are differences of course in thermal conductivity and distortion control, but for just learning how to control your power supply you will be fine.

If you do have access to stainless, With good sheared flat pieces you shoud be able to do a thin to thin (0.040) fillet with no burn thru after a bit of practice.. without backing gas or heat sinks.... Production work will almost always go better with backing and heat sinks, but they are not always available.

If you can do it without a heat sink... life will become all that much easier when one becomes available.

When backing gas is and is not required is a pretty big subject in itself.

Topic valid testing parameter ideas for cost saving change on GMAW By Metarinka Date 11-07-2008 20:49

I don't have much experience in electrode selection, but I did a large amount of cost cutting and quality analsyis based on shielding gas so I thought I would chime in.

I'd thought I get this off my mind first; consumables are a very small portion of costs for manual processes. Without knowing the specifics of your situation, I apologize if any of this information is redudant or not applicable. Often times managers will look at consumables first as they are the most obvious area of welding cost. Wire that is 10% cheaper offers an obvious cost saving difference, especially in facilities who average hundreds of thousands of pounds of filler material use per year, but consumables are generally much lower than 20% of total welding cost and therefore even a 20% difference in wire cost would only directly reduce welding cost say 2-5%. Therefore it is important to relate consumables to the much bigger factor of total welding costs like arc-on time, deposition rate and weld quality.

with that being said I decided to test consumables based upon the impact they had on overall process flow and the effect it had on such variables as: weld quality, deposition rate, travel speed, acceptable parameter range, ease of use, and overal performance under various average shop conditions. I found that it was much more important to evaluate consumable performance based on these parameters than on cost alone.

Futhermore if the process has not already been optimized, by means of maximizing filler deposition rate, increasing travel speed, minimizing distortion or spatter and other methods, than introducing a new consumable will not accurately highlight it's realistic cost impact.

For my project of evaluating shielding gases first I measured and maximized the performance of the existing product. I.e the highest realistic travel speeds, deposition rates and weld quality that could be expected under actual shop conditions. Then I recorded and monitored parameter ranges i.e min max voltage, short circuit transition voltage, spray transfer transition voltage etc. Some parameters such as travel speed, etc were averaged over multiple welders to A) check for deviation and B) give accurate samples of realistic parameter ranges under shop conditions. If a WPS calls for a WFS between 275-315 and all welders are welding at 275 then it's time to evaluate the procedure. Finally macro tests and other destructive tests where performed in order to give a realistic sample of weld quality.

The same tests were run under the new consumable and the results were compared. This meant modifying other parameters etc and restablishing realistic acceptable parameter ranges and discovering any weld quality issues (O.O.P performance, consistency etc). The prime variables we were looking at were deposition rate, travel speed, penetration and bead quality. In our case the cheaper shielding did offer a reduction in consumables cost, however the practical limit for travel speed and deposition rate were lower. Therefore by increasing consumable cost by a considerable amount (using more expensive gas) we could reduce overall cost. These cost savings would only be realized if we kept our process optimized (i.e ran parameters in the range above what was achievable under the old consumable). This is where the focus on welding skill, parameter selection and process optimization overrides consumables cost.

Testing two identical consumables from two manfacturers however might not be as conclusive as the changes in quality and parameters I would think would be smaller and less noticable. Futhermore consistency issues might not be apperant if for example they only appear on 5-10% of the spools. However the methodology should be the same
I hope that helps

Topic deposited weld metal in branches By 803056 Date 04-09-2007 19:24

In the absence of asking the manufacturer what their welding requirements are, the piping codes general require a complete joint penetration groove weld plus a reinforcing fillet weld. The size of the reinforcing fillet weld is dependent on the specific piping code, not the operating pressure.

One manufacturer that I have spoken with, will not warrantee their product unless the groove weld is a full sized complete joint penetration weld and they insist on a reinforcing fillet weld all around the fitting. Different fittings are used for different applications, i.e., pressure and other operating considerations.

Many of the integrally reinforced branch fitting I have seen in the field were not welded in accordance with the appropriate piping code and they did not meet the requirements of the manufacturer.

There are alternatives to using the integrally reinforced branch fitting (and the accompanying welds). They require some effort on the part of the design engineer to properly size the branch fitting and the reinforcement ring (if required). However, there may be an opportunity to reduce the distortion in the run pipe by minimizing the weld size requirements through design.

The intent of the integrally reinforced branch fitting is to reduce the engineering time required to design each branch connection by utilizing standardized fittings that have been designed and tested by the manufacturer. The integrally reinforced branch fitting (with full welds) eliminates the need to design (and install) reinforcing rings around the branch fitting to compensate for the volume of base metal (in the run pipe) removed to accommodate the branch.

Branch fittings that are not welded as per the manufacturer's requirements are not going to perform as they were intended. Groove welds that are not welded to completion can act as notched stress risers. What is often over looked are the stresses induced as the run pipe moves longitudinally due to changes in temperature. Those longitudinal movements induce bending loads on the branch fitting. Fatigue and cracking can result at stresses much lower than yield.

No insult is intended when I say that there are very few welders that have the training needed to perform the calculations necessary to design a branch connection in the field. However, I've had welders say that the full weld isn't required because the system isn't operating at full pressure. The same welders lose the ability to speak when they are asked what piping code is specified. They get glassy eyed when they are asked what operating temperatures, pressures, and allowable unit stresses are permitted by the applicable piping code. The glassy eyed look becomes the 1000 yard stare when they are asked "what is the magnitude of the bending forces on the branch fitting due to thermal cycling?" Contrary to the belief held by many pipe welders, few welders are qualified to make those determinations.

My advice is to contact the design professional and the manufacturer if there is a question about the welding requirements for a particular fitting and application

Topic weld stress relief By - Date 02-17-2005 22:31

Ken,
It is possible to minimize weld distortion if you can weld and vibrate at the same time. Heat input is always a big factor so minimizing local heating by skip welding about the framework would be a good start. If you can produce reasonably straight subassemblies, final assembly should go a lot smoother. You didn't mention what type of tubing was being used and it's wall thickness, which may have some bearing on your results.
There is hope.

Topic Welding stainless sheet metal By - Date 11-04-2003 08:39

Hi Jon20013!
Well - now that we've cleared that up, let's see if I can assist you in your search for some suggestions that could help in minimizing shrinkage and distortion for your stainless steel welding application that requires an "Oilcan free" overall geometric dimensional shape... I know that's what you really meant, especially adjacent to where the joints are concerned, correct??? I say this because distortion, shrinkage does'nt noticeably change the surface finish grade of the metal and for clarification purposes!!! In other words, no ripples, curves or bends where the surface lines or the surface contours should be flat, straight and continuous, correct???
Anywho, here are some other suggestions or options that might be useful for your application:
#1.) Having the capability of programming, upsloping, downsloping and pulsing your welding current, which is as you already know, dependant on the type of power source available to you would be helpful in controlling the heat input... Possibly renting or leasing the equipment could be an option here if none of these capabilities are readily available to you with your present welding equipment...

#2.) Generally speaking of course; If you're vessel requires both longitudinal and circumferential butt joints then, it would be logical to weld the longitudinal seams first and your circumferentials last as far as your overall sequence of operations, with everything else that's to be welded to the vessel in between... It's the "in between" part that's going to be difficult to control as far as distortion and shrinkage is concerned so;
#3.) If you're only going to produce a few then, shucks!!!
I apologize for not remembering the brand or manufacturer (Tempil?) of this heat sink (the name brand is HEAT) compound I used awhile back in the eighties which was available in in paint cans or caulking tubes... This compound would absorb the heat adjacent to the joints (both fillets and butts) once spread on to the material prior to welding so it would have to be applied to both members of any of the joints where other heat sinks may not be accessable! Once welding is completed, the compound readily peels right off if applied properly!!! (definitely read the instructions first with this stuff) If tee joints are to be welded, apply a coat of this stuff on the backside of the tees adjacent to the centerline of the tee and not directly on the opposite side of that centerline so that you do'nt burn the stuff because it stinks like heck when it burns, but works really great when properly applied!!!
#4.) Even when you tack the CJP's together, you must back purge the joints prior to welding or you'll never get acceptable RT's!!!
Of course, you must also backpurge the joints prior to and during welding so that the backside of the roots (penetrations) do'nt show contamination or porosity in the radiographs!!! Also, do'nt forget to cap/cover the openings and/or fittings prior to purging or else you'll be wasting alot of argon!!! Use common sense here!!!
#5.) Use an oxygen/nitrogen analyzer/indicator in order to constantly check for atmospheric contamination levels in the purge areas prior to,during and after both tacking and welding the vessel CJP joints together!!! A definite must for acceptable RT's!!! Then again, you do'nt want the welds to be just acceptable do you??? Of course not!!! You want them to be superlative!!!
#6.) use tempsticks or pyrometers to control your interpass temperatures while welding and as a welding engineer, you should have either of these items available to you. you should also calculate the interpass temps yourself for 16 gauge 304L ss...
#7.) After the welds are completed especially not too long after; Passivate and clean the welds, HAZ zones so that you minimize or even eliminate potential ISCC (Intergranual Stress Corrosion Crack) and pitting corrosion locations at or adjacent to the joints!!! Very Important!!! Especially with thin walled vessels!!! If you can, passivate and clean the joints prior to tacking and welding also, preferrably after the components are fabricated!!! Oh yeah - I almost forgot, deburr the components prior to passivation and/or assembly/tacking where the CJP's are!!! Also, if you must plasma cut openings; grind and polish kerfs and remove via polishing or preferrably passivation (because of possible inpregnation of dirt, grease film or other potential contaminants to the fusion/weld zones) any HAZ showing prior to welding if it's a CJP weld!!! In other words, use common sense here!!!

I'd be happy to assist you in greater detail but, as you know, since I do not know what Type of equipment you have available, what the actual design and/or specs. looks like; I'll have to stop here for now!!!
If you would like, e-mail me ( hanklive39@hotmail.com ) a detailed description (possibly a set of prints?) of the vessel in question, a list of your available equipment and whatever else you might feel necessary for me to assist you further unless that is, if you can take it from here!!!
Good luck you youngtimer!!! All the BEST!!!

Respectfully,

SSBN727 Run Silent... Run Deep!!!

Topic Metallurgical Question By - Date 10-17-2003 12:40

Hi everybody!
The Curse of the "BAMBINO" has struck again!!! Another Thriller in the Bronx!!! What a Great Team those Boston Red Sox are!!! I mean that sincerely!!! It could've gone either way... wait a minute! I apologize for that outburst but, I just could'nt help it!!! GO YANKEES!!!
Anywho, now that I got that off my chest, I can now somewhat (yes and no) freely talk about this and another project... You've heard of the "Maglev" or magnetically levitated high speed transportation system that has been designed and put to use by both the Germans, and the Japanese... Well - the United States is getting back into the game again also!!! I say this because, quite a few years ago we were at the cutting edge of this technology... As with alot of other well intentioned advances in new technology, the U.S. abandoned the project because of a variety of "reasons" so to speak but, mostly for lack of funding from congress...
There are many benefits with having a system like this because, of the time savings involved when one does alot of regional flying, makes long commutes in many regions where congestion is the norm, and weather plays havoc to flight schedules, and some regional airports are ever-increasingly expensive to fly out of, just to name a few... just think about it - being able to travel from Chicago to Detroit in 90 minutes by land!!! No more crowded runways!!! What a concept!!!
I'm not going to spend anymore time trying to sell this concept so, I'll just get to the point... There are mainly 2 tested, and proven designs for this new method of transportation. The German design is the one that was chosen to implemented here in the U.S. This same design has already been completed in Shanghai, China, and is scheduled to go into full service (already has started to generate revenue) in the beginning of 2004...
There were quite a few regions in this country competing to implement this project, and at the present time there are only four that show real promise... They are the Atlanta to Chattanooga project, the Baltimore to Washington D.C. project, the Los Angeles to Las Vegas project, and the Pennsylvania project... There is another project that is'nt as well known to the public which will also be implemented here in the greater Pittsburgh area... This is the one that I was referring to in my previous post... The design and Technology behind this project is totally different than the first 2 I already mentioned... The method of propulsion is the same but, how it goes about achieving this is totally new so, I'll just leave it at that (National Security Concerns)...
The Pittsburgh Section of the AWS invited the two groups to our monthly meetings so that they could present these projects for us mainly because, the amount of welding that will go into both of these designs... Normally, we have one meeting a month but, this month we had two because of the importance these projects have with respect to revitalizing the steel industry in Pittsburgh! Of course there are other reasons but, I'll leave it at that also...
The first meeting had to do with the lesser known project, and quite frankly - I was'nt too impressed with the design but then again this one is experimental in nature, and has far-reaching implications in a variety of new forms of transportation so, my guess is that the presentation was intentionally confusing...
The second Meeting was a real treat!!!
This presentation was based on how the German design is going to be implemented here in the U.S. There are alot of factors as to why Pittsburgh has the edge over the competition but, others may disagree so-maybe it would be better to discuss that some other time...
65 to 70% of the project costs will be in the engineering/design, and fabrication/construction costs mainly for the "Guideways" where the "Trains" levitate over. This is where we can lower alot of the overall costs of the original design, and alot of that was presented at the second meeting... Most important of all is the choice of steels to be used on this project which will be different from the "other project"...
A-36, and Core-ten will be used in the implementation of the German design. The thicknesses will vary from 5/8", 3/4", 1", and 1 1/4" respectively... Most of the welds will be fillets, and this is where it gets interesting because, each section of guideway will be approximately 204 ft. long so, controlling distortion will be paramount!!!
The section of the guideway where the train levitates over will be A-36.
The sections that keeps the train from travelling off the track from each side of the guideway because, basically each car "hugs" it as it travels, and yet also does'nt make contact with it., These two side sections will be made of Core-Ten steel...Thus, the space between the magnets, and the three sections of the guideway MUST be within some very close tolerances!!! Now this is where controlling, and minimizing distortion MUST to be done in a way that's unprecedented!!! This is where the Germans are quite hesitant in letting us know how they went about it in the first place... Allies huh??? Then why did they share it with the Chinese first??? I'll tell you why!!! it's because of our continuing record trade deficit, and basically unfair (to us) trade practices we have with China!!! Some of you might disagree with me but, that's why our manufacturing base is suffering so much these days!!! Other countries also do'nt play ball with us on level playing field but, China scares the crap out of me when I think about all of those people competing against us!!! One last comment, They're still in case some of us forgot, a communist nation!!! Over two or three Billion and counting!!! Sorry about that but, it just makes me want to scream (convict some of them for commiting treason) at both houses of congress!!!
However, one of this country's brightest minds has a few tricks up his sleeves to tackle this potential problem!!! The technologies being used on this project will revolutionize (yeah, I know you heard this before but, it's TRUE) large scale fabrications such as shipbuilding, bridges, buildings, and other large scale structures as we know it today!!! The steelmakers will have to ensure accuracy and repeatability unheard of today!!! I'm sure Chet, JW, Mike, Kip and the rest of you large scale fabricators would love to see this happen in earnest!!!
FEA and advanced Metrology methods will lead the way in controlling distortion. Coupled with advanced robotic systems, and cutting edge welding processes will ensure repeatability on such a large scale...
The future implications will be far reaching when this project becomes a reality, and it looks like there are enough influential people on board that have invested into this project!!! So, I'm very cautiously optimistic that I do "see the light at the other end of the tunnel" getting closer to the revitalization of the steel industry here in Pittsburgh... Who knows, I might even start rooting for the Pirates if this goes full tilt or maybe that's just wishful thinking but, like my wonderful grandmother used to say: "It does'nt cost anything to dream!"
Looking foward to your comments...

Respectfully,

SSBN727 Run Silent... Run Deep!!!