HEAVY-EQUIPMENT REPAIR: MORE THAN JUST WELDING
REMOVAL OF THE FAILED COMPONENT
The first step in welding repair is the removal of the damaged metal, by cutting away or gouging out the damaged area. It is critically important to fully grind out all cracks – even beyond what’s visible – because the slightest remnant of a defect will continue cracking even after a weld is laid over it. Removing all rough edges is also extremely important when replacing a damaged part with a new one, this will ensure proper fit-up of the replacement part.
PREPARATION OF A NEW JOINT/PART
Choosing the correct replacement/filler material is critical. All components should be replaced with a material that meets or exceeds the strength of the parent material. This ensures weld quality and longevity, and avoids premature failure.
When the new nart is fabricated it is important to bevel the edges at a 30-degree angle to assist in better welding penetration. For heavier sections of material, it is a best practice to leave a small “land” at the bottom of the joint.
Cleanliness of the welding joint is critical. It is best practice to remove all contaminants from the weld area; all rust, oils and paints must be ground or wiped away prior to welding–failure to do so will lead to a failed or weakened weld.
Preheating is another best practice that will avoid issues down the line; this is done to remove hydrogen and other gases, reduce the maximum hardness, minimize shrinkage stresses, and minimize distortion; all of which might cause cracking when an extremely hot welding arc is applied to cold steel. Preheating temperatures vary among materials. If necessary, a heat crayon can be utilized.
WELDING PROCESS
When doing repairs in the field Stick and Flux Cored welding are most commonly used. These self-shielded processes provide adequate protection of the weld bead in the outdoors. A common misstep in Flux Cored welding is wire selection; an all-position, multi-pass wire is essential. An issue I encounter regularly is porosity caused by contamination during the welding process due to poor, or no, removal of slag after each weld. I have witnessed this time and time again by those who call themselves “welders”. This is a costly problem for a company that is nothing more than laziness or ignorance—a testimony to why it is important to have the right welder.
BEYOND THE WELDING
Repair of heavy equipment goes beyond just bringing a good welder; I know excellent welders who’ve been on pipelines, built miles of fence, or repaired farm equipment and trailers for more years than I’ve been alive. All of them are lacking in one key area—the most important area. They have little to no understanding of the engineering behind this type of equipment. An understanding, which I promise you, is crucial for successful and lasting repairs; this involves knowing the equipment's design, how the equipment is designed to withstand loads and stresses, and understanding the cause of failure points, such as fatigue cracking, wear, or corrosion, and the reasoning behind the design, i.e., the science behind doubler plates. Understanding that sharp corners in metal structures are known to concentrate stress leading to fatigue failure or premature failure under high loads; knowing that rounded edges make a weld more reliable, reducing the likelihood of weld defects like incomplete penetration or porosity, and that rounded corners help improve the overall fatigue resistance of the doubler plate, by reducing the stress concentration making it more robust and structurally sound.