Later, the bracket held a heavy pump during a pressure test. No cracks, no leaks.
The lesson Marco never forgot: Welding on top of a horizontal pipe is horizontal position welding (per AWS: 2F for fillet, 2G for groove)—and it requires deliberate technique to manage gravity’s sideways pull. Ignore that, and your weld will sag, undercut, or fail when it matters most. Takeaway for your own work: When you see a horizontal joint (the weld’s length runs left-to-right), always remember—gravity is not your friend. Aim slightly upward, keep a tight arc, and watch the puddle’s lower edge like a hawk. That small adjustment separates a pretty weld from a safe weld. horizontal position in welding
Marco was a second-year welding apprentice working on a water treatment plant upgrade. His task: weld a support bracket onto a 12-inch horizontal steel pipe that carried non-potable water. The pipe was stationary, about chest-high, and the weld was a simple fillet—a perfect opportunity to practice. Later, the bracket held a heavy pump during a pressure test
Lou nodded slowly. “And the pipe is horizontal?” Ignore that, and your weld will sag, undercut,
Marco shrugged. He’d done flat welds before. He struck an arc.
Lou knelt beside him. “You fought gravity. In flat position, gravity helps you. In horizontal position, gravity pulls the puddle down . You need to aim your rod slightly upward and pause on the top edge to let the metal freeze before it sags. Also, run a stringer bead—don’t weave wide.”
Within three inches, his molten puddle sagged. The top bead looked fine, but the toe on the lower side was jagged—metal had dripped downward before solidifying. He tried speeding up, but that just created cold lap. Frustrated, he chipped off the slag and saw the truth: a weak, uneven weld with undercut along the bottom edge.