Welded joint strength vs. parent material

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The recent I-beam thread got me thinking about what I've read over the years and what does it all mean in the grand scheme of things.Specifically, how much does a properly welded joint de-rate the parent material - or is it actually just as strong?Or, is it just as strong, but only for a certain number of flexures?Here are a couple scans to help with the discussion.  I trust we can all use documentation over speculation for this topic Feel free to upload documents that disagree or agree with what I included.  Either way it will help the discussion.Last edited by MinnesotaDave; 02-12-2014 at 09:43 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Oh boy , this ought to be good.Miller xmt304,  Miller S22 p12, Miier Maxstar SD, Miller 252 w 30A, Miller super32p12, Lincoln Ranger 9, Thermal Arc 181I with spoolgun, Hypertherm 10000 ,Smith torches. Esab 161lts miniarc.
Reply:It could be instructive Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Originally Posted by MinnesotaDaveThe recent I-beam thread got me thinking about what I've read over the years and what does it all mean in the grand scheme of things.Specifically, how much does a properly welded joint de-rate the parent material - or is it actually just as strong?Or, is it just as strong, but only for a certain number of flexures?Here are a couple scans to help with the discussion.  I trust we can all use documentation over speculation for this topic Feel free to upload documents that disagree or agree with what I included.  Either way it will help the discussion.Attachment 619391
Reply:How about pictures? Attached ImagesDon’t pay any attention to meI’m just a hobbyist!CarlDynasty 300V350-Pro w/pulseSG Spool gun1937 IdealArc-300PowerArc 200ST3 SA-200sVantage 400
Reply:Originally Posted by docwelderyou'll have to excuse me cause i'm only a welder. what the heck is a flexure?
Reply:Originally Posted by CEPHow about pictures?
Reply:much more better.i.u.o.e. # 15queens, ny and sunny fla
Reply:Originally Posted by MinnesotaDaveI'm more looking for information on general fatigue over time.
Reply:oh boy, not another....
Reply:Originally Posted by kkustomzoh boy, not another....
Reply:Way beyond my pay grade...nice looking straps CEP!.  In general the filler metal exceeds the ratings of the parent metal.  The tricky bit is figuring elongation, tensile, chem related cracking tendencies and natural stress on the welded joint according to process and filler applied.  That is what engineers are for and how/why different codes are in place....to narrow down these problems.
Reply:I'll start - in my first scan weld picture 2 and 3 show a drastic difference in fatigue life just by grinding the weld flush.I was suprised by this.  Anyone else find this disturbing?Last edited by MinnesotaDave; 02-12-2014 at 09:52 PM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Tis could be some good learnin' for a lot of us.The 2nd scan taught me that it is better not to weld at all. That's gonna save me a lot of $$$!GravelThe difference between theory and practice is that in theory there is no difference.
Reply:someone higher up on the welding food chain's got to answer that one. i only weld it up after it broke.i.u.o.e. # 15queens, ny and sunny fla
Reply:Originally Posted by GravelTis could be some good learnin' for a lot of us.The 2nd scan taught me that it is better not to weld at all. That's gonna save me a lot of $$$!
Reply:Boy! information! Now I have questions; why the conservative numbers in the charts? I've never understood the figures on a box of electrodes. 6010 is approximately 60000 tensile, yet yield strength is less. The softest mild steel is stronger than your chart, is this just a huge margin of safety? The straps in the bend test; why can't I see the weld? Why is it gold colored?As we know that all weld shrinks as it cools, wouldn't a ductile filler able to deform as it cools leave the structural member with less internal stress thereby more retained strength? The James I Lincoln Book Metals and how to weld them speaks of austinitic sp? steel after minor stretching being significantly stronger than before.
Reply:Originally Posted by GravelTis could be some good learnin' for a lot of us.The 2nd scan taught me that it is better not to weld at all. That's gonna save me a lot of $$$!
Reply:All welds are stronger than the base metal,no reinforcing is needed,even using 6013. We butt weld everh dayin a bridge shop.
Reply:I would say it depends on the defect. Grade b pipe welded with 6010 properly will have a successful tensil strap. Insufficient fill could result in failure and incomplete penetration could result in failure. Slag inclusions probably wouldn't cause failure in a tensil strap. Now weld a hard steel x-70 pipe with 6010 rod and your tensil straps will probably fail regardless of proper welding technique. The reason you would grind a weld flush is if you were to exert force on a weld it has stress points at the edges of the weld that extend right into the HAZ creating a weak spot. That is why you don't see the weld in cep's photo. Also if there were any deprecation it could be hard to see without it being ground smooth. Really it is all dependent on which force you want to apply on a weld
Reply:Originally Posted by PavinsteelmanAll welds are stronger than the base metal,no reinforcing is needed,even using 6013. We butt weld everh dayin a bridge shop.
Reply:So is all that saying that welding on mild steel leaves it not as strong as the base metal before welding? I'm just a dumb truck driver so this is over my head somewhat. If so, then how do you compensate for the reduced strength of the base metal, say in a but weld situation where maximum beam strength is needed?
Reply:Originally Posted by MinnesotaDaveSpecifically, how much does a properly welded joint de-rate the parent material - or is it actually just as strong?
Reply:Originally Posted by welderjSo is all that saying that welding on mild steel leaves it not as strong as the base metal before welding? I'm just a dumb truck driver so this is over my head somewhat. If so, then how do you compensate for the reduced strength of the base metal, say in a but weld situation where maximum beam strength is needed?
Reply:Originally Posted by DSWReal key to your question is the words "properly welded". "Properly welded" would assume that the HAZ zone was correct for the material being welded as well as other details like preheat, post heat, filler type, interpass temps, hydrogen cracking and so on.Basic "mild steel" things aren't as critical as they are when you start talking about specialty alloys like high strength steels. When you start talking about steels with tensile strengths above say 70, 000 psi, all those other factors start to get pretty important in maintaining the strength of the base steel. When you start talking about really specialty steels ( 120K +), like when things are heat treated and tempered to gain strength, temps and HAZ begin to become super important.I really wished I'd had more of a basic understanding of a lot of this when I had the opportunity to learn it years ago, but at the time most of the info I was given simply went over my head.Again the real key to your question is "properly welded". With specialty steels engineers design all the parameters to maintain a given level of strength in the material. They do this both thru calculations as well as destructive testing. They 1st figure out what the calculations tell them the joint or material strength should be, then the weld up a bunch of samples and test them to destruction to determine if their calcs match the real world numbers. Then they usually add in a reasonable margin of safety figuring the monkey's in the field may not do perfect welds or might try to cut corners slightly either deliberately or thru ignorance.Little gurl methods. You wanna fasten some steel together ? Bubble gumTooth pixDuct tapeBlack glueGBMF hammerScrew gun --bad battery (see above)
Reply:Originally Posted by tommyjokingnice looking straps CEP!
Reply:ManoKai was kind enough to offer this link on fatigue strength on another thread.http://www.steel-insdag.org/teaching.../chapter32.pdfDave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Well I am glad it made ya feel good.  I am glad you said pipe welder instead of pipeliner because I certainly am not a pipeline hand,,,,nothing against or for...just not enough of to call myself one.   I am just a welder who really does not care what your joint config or process is..I will do it and well if I get paid accordingly.