Excavator Boom Repair

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I'm curious of the best way to make repairs to heavy equipment, this video is an exampleIt doesn't show the full repair but, based on the comments:1) Carbon Arc Gouging to V the crack out2) Possible grinding depending on how clean the gouging is3) End of crack hole drilled, I guess to prevent stress at end4) Straighten up the distortion in the dipper arm and remove the 5 degrees or so of axial twist (Not sure how they would do this, use Excavator hydraulics?)5) Preheat to 110 - 120 C6) Weld with 9018 , 10018 or 11018MR electrodes7) Weld fish plate front and backIt looks like several people say just #1 and #6 are needed, but the twist and separation in the boom would still be there so would break again.  How would experienced welders do it?
Reply:Cac the crack out and push down on the right side of the bucket to squeeze the crack shut to re align and weld it back together The grind flush and fish platethe original weld failed next to the bucket pin boss where crowd stick and weld met...Backed my CATMA over your CARMA oops clusmy me  What would SATAN do ?? Miller Trailblazer 302 AirPakMiller Digital Elite  Optrel Welding HatArcair K4000Suitcase 12RC / 12 VSHypertherm PM-45Rage 3 sawRusty old Truck
Reply:I'm not sure if I'm looking at welded steel fabrication or ductile iron. If ductile, don't try to weld it. If steel, I'd cut it off, clean it, V it and repair it with something more ductile 7018. The weld will shrink making some BIG stresses. 7018 will stretch more easily, grain structure bonds are stronger after minor stretching. 7018 likely will be less likely to crack again.An optimist is usually wrong, and when the unexpected happens is unprepared. A pessimist is usually right, when wrong, is delighted, and well prepared.
Reply:I've repaired a couple like that. Remove the boss completely, weld a spigot that will fit inside the boom 12" long or so to the boss, insert it into the cleaned up end of the boom and fishplate to suit after welding of course....Mike
Reply:I have done a few of these repairs. I would bevel down to 1/4" from the bottom and install weld tabs on the side of boom. use the machines force to suck up the gap. preheat and lay in a nice root pass and burn to the bottom of the crack. After that hot passes and cap. Grind flush keeping your grind marks inline with the boom rather than going across. All welding done with 7018.Thats how i did the last one that broke (400 size machine in the same spot) Its been 7 years now with no problems.Operating Engineers Local 3Lincoln SA 200Victor TorchDewalt Grinder10 lbs SledgeWhat more do ya need!
Reply:We have started to use alot of 8018-c1. the extra nickel seems to help alot on big equipment.. preheat is also your friend.
Reply:8018C-3 (1% nickel) is common for crane booms. C-1 I think is 2.5% nickel and not as common as  C-3. The higher tensile rods are similar to comparing grade 8 to grade 5 bolts. Stronger tensile but less ductility. Some guys will use bolts for bucket teeth pins. Grade 8 will snap off but grade 5 will bend and flex without breaking. If you use a carbon arc gouger, always grind it to clean metal so you don't have any chance of picking up carbon. On steel like this boom, I don't know if drilling holes at the end of the crack is necessary. On cast iron or aluminum if stops crack propagation but steel I think cracks from actual stress applied to the piece rather than heat. Preheat and letting cool slowly is good. On the fish plates, I would round the end up the stick like a half circle. On that boom repair, I'd put the fish plates on the side above the pins since there's room for them.
Reply:Had the same break at a co I used to work for, on a (remember them?) 235 Cat excavator. Mech tried fixing it twice and then company bought a new unit to simply replace the bad one. Cat sold pretty much every part on those (w)hoes. (I didnt break it! I was, however, running a '666' Koehring hoe when the boom broke right at where the two 'lift' rams connected. Didnt feel too bad about that, as several of us running it had told the office about the growing crack on top there. (had to climb up there daily to grease the top boom ram fittings) I spent a week helping the mech/welder repair it.-c-What is the sound of one knee jerking?