For material thicker than 1/8 inch in GTAW-P, what is the rule of thumb for the initial amperage for the first 0.125 inches?

• A. 2 amps per 25% of the thickness
• B. 0.25 amp per 50% of the thickness
• C. 1 amp per 25% of the thickness
• D. 0.5 amp per 25% of the thickness

Answer: (D)

In GTAW-P, starting heat input for thicker metal is controlled by a scale based on thickness, so the current isn’t a fixed number but grows with how thick the piece is. The rule of thumb for the initial portion of the weld on material thicker than 1/8 inch is to use 0.5 amp for each quarter of the thickness that you’re starting from in the first 0.125 inches. This keeps the arc stable and avoids excessive heat right at the start, which helps prevent burn-through and excessive dilution as you establish the weld bead. The other multipliers would either push heat too aggressively or aren’t aligned with this quarter-thickness scaling approach.