Welding through mill scale--for experts only? (SMAW)

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In the past I've tried to save time by not grinding off mill scale unless it's absolutely necessary, but my welds seem to turn out worse when I skip this step. I'm starting to suspect that it has reduced conductivity and causes uneven beads, because the really arc wants to jump to the existing bead rather than the unwelded mill mill scale. Or does it just take an additional level of skill to get penetration through mill scale? Or finally, is it just because I'm using E6013? (There are no fast-freeze electrodes for mild steel available where I am.)Everything I've read says that stick welding can go through mill scale, but my results definitely seem worse.In the same vein, which is less likely to screw up a joint--welding through thick mill scale, or welding through very light rust? Because I can use acid to get rid of the mill scale, but I'll probably not be able to keep it rust-free.
Reply:I stick weld through heavy mill scale daily on structural steel. The only rod we use is low hy 7018 and I have no issues. Sometimes I will run my wire wheel over the mill scale to remove a little of it. 7018 will weld through light rust and or mill scale without issues.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:We never remove the mill scale on structural.  I use 6010 to burn it in there and 7018 for the rest.  Always works fine for me.
Reply:You can weld through mill scale with stick or fluxcore.  Those filler metals have lots of additives that will help break down the mill scale and prevent it from becoming oxide inclusions in the welds.  Your not imagining things when you mentioned seeing that the arc wanders and doesn't run as smoothly when welding over mill scale.That said, in a perfect world, you would always remove any surface contamination prior to welding.  Even stick electrodes and flux cored wires have a limited ability to cope with contamination.  Heavy rust, loose mill scale, paint, any kind of grease or oily residue should be cleaned from the weld vicinity.  Failing to do so produces a weld with less than ideal properties.  Can you weld through heavy rust with 6010 or 6011 electrodes, or Fluxcored wires?  yes.  Will you get the best strength and toughness when doing so?  Probably not.  Will the weld hold?  It all depends on the specific situation.  This is where the welder has to exercise some good judgement.This becomes more critical with MIG and TIG.  Solid wire filler metals have small additions of additives that prevent contamination, like mill scale, from creating defects in the weld.  Metal cored wires fall somewhere between MIG/TIG and Stick/Fluxcored in terms of abilities to deal with mill scale.  But its much easier to exceed the capabilities of these filler metals to cope with surface contamination.  See for yourself.  Run a bead on some Hot rolled pickled and oiled steel straight from the service center.  Then take another piece of that same steel and clean off the oil with some degreaser and take a grinding wheel and clean an area to bright metal.  Weld again with the same settings, position, technique, etc.  You'll see a marked difference.  If you really want to see the different repeat that test with an inside corner fillet weld.  Odds are you'll need to adjust the weld voltage/amperage/wirefeed speed because the settings needed for dirty base metal will be nothing like those that are best on clean steel.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:For those that don't want to take time to prepare the area to welded they'd be better off to stick w/ 6010/6011.                                                         MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:Originally Posted by mla2ofusFor those that don't want to take time to prepare the area to welded they'd be better off to stick w/ 6010/6011.                                                         Mike
Reply:Can't run 6010 or 6011 on structural. It isn't up to code.7018 welds fine over mill scale.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:Back in my false work days, they'd run you off for taking the time to remove the mill scale. Only time we were allowed to remove the mill scale was when doing full penetration beam splices.Don’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Not trying to start a pissin' match, but probably 99% those that complain about mill scale are hobbyists and have plenty of time to remove it if it's a problem for them. Those getting paid to do it soon learn to work thru it.                                                           JMHO,                                                                    MikeOl' Stonebreaker  "Experience is the name everyone gives to their mistakes"Hobart G-213 portableMiller 175 migMiller thunderbolt ac/dc stick Victor O/A setupMakita chop saw
Reply:A lot of hobbyists are welding thin metal that has mill-scale as a fair percentage of the metal thickness.If you can't just burn it off with higher amps, you would have to clean it some how.
Reply:I have followed this thread with interest as it certainly covers both pros and cons to mill scale removal and the benefits of it or not. Simply put, many FCAW/GMAW/MCAW wire types, SMAW stick electrodes, GTAW rods, and even RG consumables have additives/formulations that address welding through mill scale without it's removal. This doesn't completely address the issue though. Grinding will always be beneficial to the resulting welding deposits that have been deposited on ground materials. Ease of application, economics, intended purpose, and type of service will generally be the best reason for grinding or not in most commercial applications. If it is a home situation, then the choice will likely be how much time you wish to invest or have to invest or the level of pride that you take in your finished project.  If you are a structural welder and are charged with doing moment connections on a high-rise there is a good possibility that you might take the time to grind or be required to grind before proceeding with welding. If you are a welder who is working on military projects or other government covered work you might very well be doing a bit of grinding before you go about doing your welding.If you are asking why I mention these instances take your own experiences and consider the differences in the finished beads on something that has been ground clean or something that has been welded without removal of the scale, rust, oils, greases, paints, or other things that can be considered as contaminants even if these issues are slight. Most of the time if you consider a vertical weld that has been performed on structural beams without removal of the heavy scales you will likely agree that the chances of undercutting the toe of a weld is much more likely when the joint is untouched as opposed to ground. You might also notice that the finished profile of a bead on clean/ground joints appears and generally is much better tied in at the toes and also has a more desirable profile than one that has been done on unprepared steel. If you had the ability to test finished welds to a fine degree you would likely find that there are subtle differences in some instances and more pronounced ones in others. Those things have to do with items such as strength, proneness to fracture, impact toughness, etc. When time and situation allows I will always utilize grinding as a part of the fit-up regimen on items that I weld. Time, money, the boss, will ultimately influence a grind or no grind decision. Good conversation folks. Best regards, Allanaevald
Reply:allan; i'm sure you're 100% correct however the last time i welded moment plates i don't remember there being a grinder on the job. Attached Imagesi.u.o.e. # 15queens, ny and sunny fla
Reply:Originally Posted by docwelderhowever the last time i welded moment plates i don't remember there being a grinder on the job.
Reply:Originally Posted by CEPReally? WOW! I've worked for some cheap a$$ companies before. I've worked for companies who would only give you one contact tip per week, and one clear lens per week. But seems as we always had a grinder on site. Might not be able to find it, but it was there somewhere.
Reply:Welded plenty of moment plates myself, I don't grind em. Weld em up. If they're heavily rusted I'll run the wire wheel over em prior to welding.Last edited by snoeproe; 11-08-2014 at 02:15 PM.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:To reply to those who weld without grinding, I am not saying that it can't be done and isn't done, I am saying that it is cheap insurance to do so and as comments to that effect have been made, I agree. Fortunately, proper engineering and generally sound welding practices are in place much of the time and even shortfalls won't compromise the overall welding that is in place on many projects. Personally, I have made welds with out any additional preparation, have used wire brushes (both manual and powered), have used pneumatic needle scalers, have welded on blasted materials, have welded on ground joints, have welded on chemically wiped and prepped joints. Regardless of the condition, you make the welds happen and if your skills aren't up to par, you do repairs or get sent down the road. To reiterate some of my prior comments, the codes that are in place, the purpose of the welding, the conditions, etc. will truly dictate the actual requirements that apply to a successful weld. Best regards, AllanLast edited by aevald; 11-08-2014 at 04:43 PM.aevald