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stray arc strikes, temp fitments & stress pts

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  • stray arc strikes, temp fitments & stress pts

    I've always heard stray arc strikes cause stress points and are viewed as defects. So, why are temporary fitments allowed? Wouldn't those also induce stress points? By temp fitments I'm thinking of pad eyes, aliment jigs etc. Is there some procedure to follow when removing them to relieve stresses or is it completely a non-issue? If the later why?

  • #2
    Here are some pictures of an arc strike. Down in the strike crater you can see the "nugget" or melted metal. Inside of the nugget there are more than a dozen solidification cracks. Also on the outside of the nugget you can see that there is extreme overlap which will reduce the included angle at the toe to zero. The crater also has a reduced section now without any transitional surfaces to allow the tension on the material surface (where most of it transfers) to flow freely. Instead it is producing all of these risers in a very small location. since we know location is everything you can show a model where they are all combined and have a much larger effect as a single indication compared to just adding up this one and that one.

    We also need to consider the effect of such a rapid heating and cooling cycle. The material depending on its type may produce and likely will extremely hard areas in the weld metal and in the HAZ.


    Temporary weld on attachments on the other hand will most of the time be accompanied by some grinding, longer heat cycles, some type of finishing and altogether just better care than an arc strike.

    Hope this helps
    Attached Files

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    • #3
      That was very interesting! I learned a bunch.

      I can understand why stray strikes are bad but still don't quite understand why application/removal of temporary fitments aren't. In the later case the homogenous base metal is being melted and combined w/ another metal. In that regard doesn't the weld and subsequent removal process form some sort of discontinuity(ies)? This is done all the time so it must be 'safe'. However, it seems as though some method or procedure must be followed to make sure the out come is good.

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      • #4
        Try the search function for arc strikes. Someone posted a great link to a lot of info regarding arc strikes not to long ago.
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        • #5
          This is kind of an apples and oranges discussion. As Diamonback said, arc strikes leave a point with many stress risers for cracks to start. After removing a temporary fitting, the area is usually ground down removing those potential stress risers. After removing a temporary fitting the HAZ is still there, but has nothing to do with the stress risers of an arc strike. If the HAZ is a potential failure point on critical projects, whether from a temp. fitting or at the final welds, the whole piece is usually annealed and heat treated.
          Sometimes there's no second chances.

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          • #6
            Originally posted by HayFarmer View Post
            That was very interesting! I learned a bunch.

            I can understand why stray strikes are bad but still don't quite understand why application/removal of temporary fitments aren't. In the later case the homogenous base metal is being melted and combined w/ another metal. In that regard doesn't the weld and subsequent removal process form some sort of discontinuity(ies)? This is done all the time so it must be 'safe'. However, it seems as though some method or procedure must be followed to make sure the out come is good.
            As Dave mentioned the HAZ really isn't an issue. Unless there is an initiation site such as a crack or overlap that will concentrate the stress and begin the initiation the HAZ from an arc strike or temporary fitment has the potential of remaining free of any indications. That is why they are ground down and often sanded to remove grind marks which can be stress risers in themselves.

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            • #7
              arc strikes

              a arc strike happens in a split second, there is no real heat soak taking place.its a quick heat cycle causing martensite ( very hard structure ) this is why it is extremely difficult to file out, the file just glides over the top.
              As for small tack welds the idea is to make them about 1/2-1" long depending on the material thickness. this is long enough to get a good heat soak into the parent material and a longer cool down, eliminating a martensite structure. a weld procedure should be followed for code work, even for tacking and a high enough pre-heat temp should be used to avoid quenching.
              this is in laymens terms,there is a bit more to it than that.
              hope this helps.PS martinsite leads to cracks in a stressed weldment!
              Last edited by maharg; 06-09-2010, 07:32 PM.

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              • #8
                Arc strikes, fast and sudden, shouldn't be there, but do happen. Am presently on a nickel project on which 2 men work steady doing pickups on removed temporary attachments and unfortunate arc strikes. Procedure is to grind flush and excavate any sign of inclusion in base metal. Often an arc strike will produce a single pore or porosity. If weld is needed, area is preheated to 125 F. Final blending must produce virtually no depth in base metal. Area is then dye pentetrant tested. On the completed project, there will be a few thousand of these.

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                • #9
                  Originally posted by OldSparks View Post
                  Arc strikes, fast and sudden, shouldn't be there, but do happen. Am presently on a nickel project on which 2 men work steady doing pickups on removed temporary attachments and unfortunate arc strikes. Procedure is to grind flush and excavate any sign of inclusion in base metal. Often an arc strike will produce a single pore or porosity. If weld is needed, area is preheated to 125 F. Final blending must produce virtually no depth in base metal. Area is then dye pentetrant tested. On the completed project, there will be a few thousand of these.
                  Wow, that's alot of stinger handling mistakes! If the arc strikes were that important, I think I would specify tig or rc mig/flux as the process to be used. Unwanted arc strikes are much less common with tig and remote control mig than with stick and volt sense mig/flux on a machine with no contactor.
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                  • #10
                    Originally posted by OldSparks View Post
                    Am presently on a nickel project on which 2 men work steady doing pickups on removed temporary attachments and unfortunate arc strikes.
                    Originally posted by Desertrider33 View Post
                    Wow, that's alot of stinger handling mistakes!
                    Maybe you missed the part about removed temporary attachments, I'm pretty sure they aren't spending the whole time dealing with arc strikes... if they were I'd think they would be looking for some new employees.
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                    • #11
                      c wagner.....thanks for clarifying that. Pick-up repairs are done the same whether they are marks left by arc, hammer, grinder, clamps or anything else that appears to be deeper then the primer paint. Biggest cause of arc marks would be trying to get full use out of each rod. The inconel rod we're using can get be pretty fussy about relighting when you're just tacking. At four times the cost of stainless you don't like thowing out any long stubs. It's possible to go for days with nice clean restarts but not forever.

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                      • #12
                        Thx...for all the replies, I learned a lot!

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                        • #13
                          Originally posted by OldSparks View Post
                          Biggest cause of arc marks would be trying to get full use out of each rod. The inconel rod we're using can get be pretty fussy about relighting when you're just tacking. At four times the cost of stainless you don't like thowing out any long stubs. It's possible to go for days with nice clean restarts but not forever.
                          Interesting, I've never welded inconel so that was an interesting piece of info.
                          Thanks.
                          at home:
                          2012 325 Trailblazer EFI with Excel power
                          2007 302 Trailblazer with the Robin SOLD
                          2008 Suitcase 12RC
                          Spoolmatic 30A
                          WC-24
                          2009 Dynasty 200DX
                          2000 XMT 304
                          2008 Thermal Dynamics Cutmaster 52
                          Sold:MM130XP
                          Sold:MM 251
                          Sold:CST 280

                          at work:
                          Invision 350MP
                          Dynasty 350
                          Millermatic 350P
                          Retired:Shopmaster 300 with a HF-251

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                          • #14
                            Arc Strike/ Arc Damage

                            Hello!!, it is the first time that I consult to a forum like this. I'd like to ask if there is a specific way to rework or remove the arc strikes when these seem to be superficial? and also I'd like to know...what is the probability of a failiure on the reworked area?

                            Thanks.

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                            • #15
                              What are you building that requires so much attention to stresses created by tacking and arc strikes...???

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