weakest joint

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Is there a weakest joint in welding and if so what is it? and why
Reply:Butts, Laps and T's.   No one is inherently weaker than another, though a structure can have a poor joint design for the direction of the load, which may make it too weak for the application.MM350P/Python/Q300MM175/Q300DialarcHFHTP MIG200PowCon300SMHypertherm380ThermalArc185Purox oaF350CrewCab4x4LoadNGo utilitybedBobcat250XMT304/Optima/SpoolmaticSuitcase12RC/Q300Suitcase8RC/Q400Passport/Q300Smith op
Reply:It is all in the applicationkeith The older the boys, the more expensive the TOYS!!Previous owned;Linde 300 Amp welderMiller Gas drv welder, Tumbstone,Dayton Miller ac to dc converter,High frequency unitLongevity LS60PCurrrently owned;Longevity WeldAll 200PI
Reply:There's a myriad number of joints in any structure.It can't be simplified IMHO.Closest you could come to "weakest" would be a joint that's under pure tension I would imagine.  It would be subject to tearout.Strongest joints are joints where the joint is in shear.  The force applied either in  line with the weld, or transverse to the weld.None of the above takes into consideration the full "real world" possible stress.  Torque, impact, etc.It's hard to pin down.  Most failures are in the design of the structure, not the welds.  Improper allowances for various stress loading  scenarios.It all depends...........Besides, I ain't no engineer"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Ooooooooo tech stuff!!!!!!!!!!!!!!!!!!!!!!! ROFLMAO"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Yeah, but you make it understandable for people like me.MarkI haven't always been a nurse........Craftsman 12"x36" LatheEnco G-30B MillHobart Handler 175Lincoln WeldandPower 225 AC/DC G-7 CV/CCAdd a Foot Pedal to a Harbor Freight Chicago Electric 165A DC TIG PapaLion's Gate Build
Reply:Weakest joint, a poorly welded one. I can think of over a half dozen reasons almost instantly, undercut, slag inclusions, poor penetration, etc....No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:If all things are equal, i.e. fit up, cleanliness, technique, current, electrode quality, skill of operator, I think a seam joint is the weakest but that is not an absolute statement.
Reply:Some more food for thoughtYou can't overlook the qualities of the base/parent metal.To keep it simple, let's take A-36 mild steelYou can weld it with a wide variety of filler materials.  It's very forgiving material.  The HAZ isn't subject to changes like some other higher carbon steels.  To a degree, all things being relative.You can use a 70xx filler, but what is the true strength of that joint????Now, I'm no engineer.........But kick this around.Sure, you've used a high tensile strength rod, let's say 7018.  You're gettin' a warm fuzzy thinking that you've got a 70kpsi joint.But do you really have the strength you think you have????????????I FEEL THAT YOU DON'T!!Remember, we're working with 36kpsi steel!!I've seen tearout below the weld.  The base metal was literally not strong enough to hold the BEAD.  Think about it.  You can use high tensile filler until the cows come home, but ultimately the strength is derived from utilizing the PARENT METAL to it's fullest potential.Now we're getting into length of welds, reinforced welds, etc.The entire purpose, might be wrong here......bear with me, of a reinforced multi pass weld on let's say A-36, is to spread the "holding" force over an increased surface.  You're spreading the load over a wider area.  THE WELD ITSELF IS NOT HOLDING THE LOAD.  THE PARENT METAL IS HOLDING THE LOAD.Forget all you hear about the Holy Grail of penetration.  TO A CERTAIN DEGREE.  Ultimately it's the parent metal we're joining, and we are living with the weakness of the parent metal in relation to the filler material.  You can do a full penetration joint, but you're still joining A-36It's the steel doing the work, not the weldNow let's get back to shear strength, and tensile strengthSteel derives it's great strength from it's tensile strength.  Period.  It's the most predictable attribute of steel.Yes, there's the compressive strength.  Theoretically huge, EXCEPT FOR BUCKLING.But tensile strength isn't limited to pure "tensile" strength.  IE pulling on it.Tensile strength coupled with a properly designed weldment, placed in shear, is one powerful puppy.Let's do an example..............Try holding a pickup truck up in the air with a 1" wide strip of 1/4 A-36 by hanging the truck off the strip in like a chain.  The upper part of the strip welded to an stationary object that will withstand the load.  Ain't happenin' folks  I don't give a dam how good the weld is across that 1", scratch one pickupNow, take the same 1" strip of metal, weld it to the same stationary object, but alongside and paralel to the object.  Maybe about 3" worth.  You can place the same pickup on TOP of that strip, and it will be there until the the cows come homeYou've placed it in shear.  And it's stronger..The line is blurred at this point.  It's a combination of tensile, and compressive strength literally on the atomic level.  Both forces are at work. Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammLet's do an example..............Try holding a pickup truck up in the air with a 1" wide strip of 1/4 A-36 by hanging the truck off the strip in like a chain.  The upper part of the strip welded to an stationary object that will withstand the load.  Ain't happenin' folks  I don't give a dam how good the weld is across that 1", scratch one pickup.
Reply:Ok, make it heavier, and see which design wins.Probably shoulda used a bigger example"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Apples to apples for weld size would be good too.My name's not Jim....
Reply:I think that's where your missing the point.We are definitely focused on weld size.  Length of weld, and stress on weldYou have 2" of fillet on the vertical strip(both sides), while you have 6" of fillet on the strip in shear.A longer weld spreads the load to a much greater surface.Just considering the weld in a vacuum so to speak."Any day above ground is a good day"http://www.farmersamm.com/
Reply:We're still limited by the parent metal.  But we're looking at two different attributes of the parent metal, and how it handles a load"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Even holding to the the 2" of total weld, I still feel that it will hold more in shear than in tension"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammYou have 2" of fillet on the vertical strip(both sides), while you have 6" of fillet on the strip in shear.A longer weld spreads the load to a much greater surface.
Reply:Originally Posted by farmersammEven holding to the the 2" of total weld, I still feel that it will hold more in shear than in tension
Reply:I just caught this thread.The first couple responses covered the initial question. Then things went off on a tangent. A couple points on the tangent: The YEILD for A36 is 36KSI minimum. The tensile strength is typically up in the high 60's (58KSI min, 80KSI max), which is a pretty good match for 60XX and 70XX welding fillers in ultimate strength. The welding fillers generally have a higher yeild than A36. Also note that tensile strength is higher then shear. Generally by a pretty good factor, assumed to be 2 in many engineering applications.
Reply:A welded joint. We use welded joints as a compromise to to billet construction. Mighty hard to forge a building out of a single homologous chunk of material.
Reply:Depends on how old you areEd Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:I guess I have the wrong idea.I suppose it's why I don't trust a single lifting lug.  Or if I have a single lug, making it longer where it's welded to the beam or plate.My intuition sometimes gets me into trouble as far as overcompensating, or seeing things incorrectly.Guess it's an inherant distrust of welds."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by DesertRider33Butts, Laps and T's.   No one is inherently weaker than another, though a structure can have a poor joint design for the direction of the load, which may make it too weak for the application.