This video documents the repair of a broken Kelly bar from a 1000-size drill rig, a recurring issue attributed to high-stress concentration from the rollers at full drilling depth. The repair process involves cutting out the fractured section with an oxy-fuel torch, followed by precise beveling of the ends using a grinder to ensure a proper root gap for welding. A significant challenge encountered is the bar's magnetization, leading the presenter to opt for flux-core welding wire over stick welding. The welding process emphasizes consistent heat, good root penetration, and continuous passes to minimize warping, resulting in a functionally robust, wide "tractor weld" despite its rough aesthetic.
Summarizing the Kelly Bar Repair: From Breakage to Weld
0:02 Project Introduction: The video begins with the project of repairing a broken Kelly bar from a smaller, 1000-size drill rig, noting that this particular bar had been previously repaired by the presenter and broke again.
0:20 Failure Analysis: The break is identified as occurring in a spot that experiences intense stress from the rig's rollers, especially when the bar is at full depth, causing a twisting force that concentrates at this specific area. This stress point cannot be avoided by adjusting the bar's position.
2:01 Preparation for Welding: The repair involves cutting back a couple of inches from each side of the break to reach clean material using an oxy-fuel torch. The roughly cut ends are then precisely beveled using a grinder, aiming for a 1/8 to 3/32 inch gap to ensure a strong root pass.
20:26 Magnetization Challenge: A key difficulty encountered is that the Kelly bar is magnetized, which makes stick welding (especially with 7018 electrodes) problematic. The presenter decides to use flux-core welding wire as a more suitable alternative.
20:32 Preheating and Alignment: The bar requires preheating before welding. Due to the bar's worn ends and natural twist from previous repairs, achieving perfect straightness is difficult, relying on visual alignment rather than precise measurements with a straight edge. Tacks are applied to hold the sections in place.
25:30 Welding Process: The welding proceeds with multiple passes, prioritizing good root penetration (evidenced by "keyholing"). The presenter emphasizes continuous welding to prevent warping and to maintain heat in the part.
38:55 Completed Weld: The repair culminates in a large, robust "tractor weld," approximately 3/4 to 7/8 inches wide. Despite its "unpretty" appearance, the weld is deemed strong and functionally sound, with consistent flushness.
39:56 Welding Details: The specific materials and settings used are 0.045 Hobart Fab Shield 21B flux-core wire, roughly 21-22 volts (adjusted for voltage drop due to cable length), and a wire feed speed around the 125 range.