456A Study Guide 2026

A bird's nest is a tangled mass of wire that bunches up at the drive rolls. It occurs when the wire cannot feed through the gun — causes include a kinked or clogged liner, worn or wrong-sized contact tip, incorrect drive roll tension, contaminated wire, or a sharp bend in the gun cable. It requires stopping, cutting the tangle, and fixing the root cause.

A carburizing flame has excess acetylene, producing a luminous feather that adds carbon to the weld pool — useful for hard-facing and high-carbon steel applications.

Cold cracking (HIC) in GTAW occurs when hydrogen absorbed during welding diffuses to high-stress areas (typically the HAZ) as the weld cools. Prevention includes: preheating to slow cooling and allow hydrogen diffusion, using clean (dry, oxide-free) base metal, minimizing moisture in the shielding gas, and PWHT for thick/restrained joints. GTAW inherently has lower hydrogen than SMAW but is not immune.

For DCEN GTAW, the tungsten should be ground to a point with the length of the taper equal to approximately 2–2.5× the electrode diameter. Grinding should be done longitudinally (along the length of the electrode) to prevent spiral arc deviation. A consistent taper angle concentrates the arc and provides good penetration.

SMAW uses a constant current (CC) power source, also called a 'drooper.' The output amperage remains relatively constant even if arc length changes, while voltage varies. This characteristic allows the welder to manually control arc length without causing large swings in current.

Centreline solidification cracking occurs when the last liquid (enriched in impurities like S and P) in the weld pool solidifies under tensile shrinkage stress. A weld bead that is deeper than it is wide (W/D 1 distributes the liquid at the top surface where stresses are lower and prevents centreline crack formation.