456A TIG (GTAW - Gas Tungsten Arc Welding) 3

Question 1

What is the 'keyhole technique' in GTAW root pass welding and when is it used?

Accepted Answer

A small hole is melted through the root opening, with filler metal closing the hole as the torch advances, ensuring full penetration

Answer

The keyhole technique involves melting a small through-hole at the leading edge of the weld pool. As the torch advances, filler metal is added to close the trailing edge of the hole. This technique guarantees complete root penetration and is commonly used for open-butt pipe roots in stainless steel, titanium, and precision piping applications.

Question 2

What is the maximum contamination colour acceptable on a completed GTAW weld in Grade 2 titanium, per industry standards?

Accepted Answer

Bright silver or light straw/gold — blue, purple, or grey indicates contamination and requires rejection

Answer

Titanium weld colour is a direct indicator of oxidation level. Silver is ideal; light straw/gold indicates minor oxidation that is usually acceptable. Blue indicates significant oxygen/nitrogen pickup; purple and grey indicate severe contamination. Contaminated welds have reduced ductility, toughness, and corrosion resistance and are typically rejected in aerospace and critical piping applications.

Question 3

What is the hot-wire GTAW process and what is its advantage?

Accepted Answer

Filler wire is resistance-heated before entering the arc, increasing deposition rate without adding arc heat to the base metal

Answer

Hot-wire GTAW uses AC resistance heating to preheat the filler wire to near its melting point before it enters the GTAW arc. This dramatically increases deposition rate (up to 4× over cold wire GTAW) without proportionally increasing heat input to the base metal, making it suitable for cladding and overlay applications on large components.

Question 4

What is 'cold cracking' (hydrogen-induced cracking) in GTAW welds on high-strength low-alloy (HSLA) steel and how is it prevented?

Accepted Answer

Cracking that occurs after the weld cools, caused by hydrogen diffusion; prevented by preheat, low-hydrogen filler, clean base metal, and PWHT

Answer

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.

Question 5

What is the correct method for adding filler metal to the GTAW weld pool?

Accepted Answer

Feed the rod at a low angle (15–20°) into the leading edge of the pool, withdrawing it slightly on each addition without touching the tungsten

Answer

Filler metal is fed at a shallow angle (15–20°) into the front edge of the molten pool using a dipping or flowing motion. The rod must not touch the tungsten (which would contaminate the electrode) or be placed directly in the arc (which would cause spattering). The filler melts by contact with the pool, not by the arc directly.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A TIG (GTAW - Gas Tungsten Arc Welding) 3