Cracked beside the weld

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Repaired some cracks on a Vibratory plow,material is about an inch and a half thick. Its the reciever for the Plow Blade.Ground existing cracks down to solid stuff,vee'd the crack and used 7018's,multiple passes.Tried to keep from getting things too hotA couple days later,a crack about an inch long showed up.  Its a couple inches to the left of any welds. Any ideas? something I did/didn't do?
Reply:Might well have been there all along and didn't make itself known until it became the new weakest area.  Fix it like you did the other.Two turn tables and a microphone.
Reply:Have any pictures?  When you say"Vibratory Plow" I have like a Ditch Witch cable trencher in mind is that when you talking about?  Has it been used since welding it?
Reply:I agree with Pangea. It was probably already there, and the heating and cooling of welding made it visible. Repair and expect more...
Reply:1 1/2 thick is heavy stuff. I'd grind or gouge out all exisisting cracks. Pre heat the entire area, then re weld with 7018. Preheating the area may make more cracks noticable.JasonLincoln Idealarc 250 stick/tigThermal Dynamics Cutmaster 52Miller Bobcat 250Torchmate CNC tableThermal Arc Hefty 2Ironworkers Local 720
Reply:thanks for the replies.  I was thinkin along the lines that it was already there and showed up with the welding.Tigwldr...no pics,and this Plow is roughly the size of a D-6 Cat dozer.Any other Rod y'all could  suggest that would be better than 7018? I have some 8010's,and some 11018's would either of those be better?
Reply:You can always go up in strength, but I'd stay with a low hydrogen rod. It doesn't seem to be your weld failing, though, so it probably won't help a lot. Preheat to around 250 is a good idea for 1" and thicker.Last edited by welds4d; 05-07-2011 at 11:28 PM.
Reply:Grind any paint and rust away about 4 inches out from the original repair to a smooth finish and preheat and look for cracks, try to put some stress on the part and check again for additional cracks.  I know you can do magnetic particle testing for cracks and I think a dye test will also show cracks that you cant see.
Reply:Originally Posted by drillmanRepaired some cracks on a Vibratory plow,material is about an inch and a half thick. Its the reciever for the Plow Blade.Ground existing cracks down to solid stuff,vee'd the crack and used 7018's,multiple passes.Tried to keep from getting things too hotA couple days later,a crack about an inch long showed up.  Its a couple inches to the left of any welds. Any ideas? something I did/didn't do?
Reply:A couple places that i repaired were where factory welds had cracked...these are fine...no cracks at repair.  The crack happened 2 inches from a repair and 6 inches from any factory welds/joints,and it was after the Plow had run a couple days.....and they're using a Tow Dozer to pull it because of soil conditions.There's no shop,or controlled environment,all these fixes are done in the field so all the suggestions so far make sense.  I'll try to get some pics and post them here this coming week.Thanks for all the help so far
Reply:Originally Posted by drillmanA couple places that i repaired were where factory welds had cracked...these are fine...no cracks at repair.  The crack happened 2 inches from a repair and 6 inches from any factory welds/joints,and it was after the Plow had run a couple days.....and they're using a Tow Dozer to pull it because of soil conditions.There's no shop,or controlled environment,all these fixes are done in the field so all the suggestions so far make sense.  I'll try to get some pics and post them here this coming week.Thanks for all the help so far
Reply:Your repair welds are holding but the plow is cracking now in other places.  If this is the case then either keep welding up the cracks or start adding reinforcements to take some of the loads.  Thats my guess anyway.Material gets brittle after its be worked hard for years and this could be the case.  If it is then its fatigue.  Beef it up should fix it (or make it start cracking somewhere else)  Good luck
Reply:Just my .02 cents.I don't see preheat mentioned in the OP's procedure. D1.1 calls for preheating of most steel above 1 1/2" to 150F. I agree that the new cracks are not new they have just now become the weakest part .Vibratory  sounds to me like cyclic fatigue. If this machine vibrates could the place where the new cracks are be experiencing a cyclic harmonic. If so changing the shape of that part would likely change the harmonic. Short answer add a gusset to change the harmonic of the part? Just thinking out loud, here
Reply:Originally Posted by SandyVibratory plows are a stress factory to begin with. Extreme draw bar pull, extreme heat, torque & phenomenal stresses from all directions if it's articulating, extreme vibration all added together is a classic case of how to make manufacturers cry.  Put one on something close to a D6 then add a tow cat and you're in for a tough job just keepin it in the ground and making money. But hey, if it's gitting the job done, and keeping up with the project schedule it's considered a necessary sacrifice. Job superintendants don't always have much choice in how they look at things. They're given a job, a schedule and some equipment and told to "make it happen" so occasionally some equipment has to die for the money gods. Sounds like you're doing a good job keepin it alive. Having a plow crew depending on you ain't always a pleasant place to be. When the plow is down, everybody is down and the welder gets the blaim. When the plow is rolling hundred dollar bills out of the plow slot, the super gets the credit. Good work, good luck.
Reply:Two inches from a weld would make it unlikely the weld is at fault. Likely materials for that would be T-1, 1040-45 and 4130. The 1045 and 4130 need lots of pre-heat and still tend to crack at the toe or centerbead, if it's T-1 that's degraded from too many repairs it will fail some distance from the toe of the weld but not that far I would think.My guess is the reciever is at its limits and could go at any scratch, ding, weld berry etc. at the surface.Matt
Reply:A general rule with structural steel is that you must preheat if the material is over 3/4 inch thick.  This applies to structural which is commonly a mild steel.  In applications where parts are under high stress,  fatigue, and are likely an alloy of some sort preheat is mandatory.  Think of it this way.  Will preheating before welding cause problems?  The answer in that it will not.  When in doubt PREHEAT!
Reply:Three things to do when welding thick steel (in general):1.  Preheat.2.  Preheat.3.  Preheat.Notice a pattern there?  Next, after preheat :lol:  , is that -sometimes- gussets or other structural reinforcement is helpful or necessary.  But not always.  By changing the structure, you may well beef up one area/section and thus shift the weak point/area to someplace else.And as mentioned, thick steel and especially thick 'structural' steel that may well be a 'higher alloy' than plain old low-carbon steel, really-really needs 'proper' procedures.  Preheat  , cleaning, filler, etc.And "fatigue" usually does NOT 'cause the material to get more brittle'.  Fatigue failure is fatigue failure, work hardening is work hardening, and the two are NOT the same thing.  They may be related (stress cycling  can cause work hardening in some alloys, and 'excessive' stress cycling WILL cause fatigue failure ) but they are not, strictly speaking, the same thing.    The best laid schemes ... Gang oft agley ...
Reply:it might be a higher grade of steel.....