When to Deploy Dual-Process for Certification-Friendly Welds
GTAW (TIG) and GMAW (MIG) each bring strengths to structural welding. GTAW offers precise control, clean starts, and superior fusion in critical root passes, but it is slower. GMAW deposits metal quickly and handles larger fill sections well, but it can introduce more heat and distortion if not managed. For critical structures, a thoughtful dual-process approach can combine the best of both worlds while keeping certification requirements in focus.
Thin sections and root passes
In thin-walled joints, you typically want precise fusion with minimal heat input. A GTAW root pass often yields the best bead geometry and penetration control. If the code allows, follow with a GMAW fill pass to complete the weld more quickly while maintaining the same joint configuration. For some codes, the root and final passes must be the same process; in others, a dual-process approach is permitted as long as heat input and documentation stay within specification. For more on how thickness affects process choice, see our guide on thick-to-thin joints.
Thick sections and dual-process strategy
Thick joints benefit from a high-deposition process for the bulk metal, with GTAW reserved for critical root control and key features. A typical sequence is a GTAW root pass to ensure full penetration and a clean stop, followed by GMAW for fill and contour. This reduces overall heat input while preserving fusion quality in the root. When planning, consider fixture accuracy, distortion control, and code requirements; you may need to document heat input per weld and the process change per segment. For a structured approach to certification planning, check our certification cycle.
Certification considerations
Certification-testing bodies often look for repeatable, auditable weld procedures. Dual-process welds are acceptable when the test plan explicitly permits them and the heat input is controlled. Use a consistent sequence and record process parameters so testers can verify your approach. A data-driven certification prep method helps align heat input, process changes, and inspection criteria across welds; see our data-driven certification prep article for details.
Practical example
Consider a 1-inch-thick structural steel butt joint. Root with GTAW to establish penetration and bead shape, then switch to GMAW to deposit the fill metal and finish the weld profile. Maintain tight heat input and avoid overheating the heat-affected zone. If the project requires symmetrical cooling, plan a reverse-pass sequence and verify distortion with fixtures. For real-world test scenarios, you can study our guidance on certification testing under pressure.
In practice, a dual-process approach should be pre-planned in the weld procedure specification and training. Keep the process changes documented, and practice under realistic mock conditions to ensure consistency across welds and inspectors’ eyes.
