456A TIG (GTAW - Gas Tungsten Arc Welding) 4

Question 1

What is the minimum purity level of argon shielding gas required for GTAW of stainless steel and titanium?

Accepted Answer

99.995% (Grade 5.0 or higher)

Answer

GTAW of reactive and sensitive metals requires high-purity argon (Grade 5.0, 99.995% pure) to prevent contamination. Even small amounts of oxygen, moisture, or nitrogen in the shielding gas can cause porosity, embrittlement, or loss of corrosion resistance. For titanium, Grade 5.0 or higher is mandatory.

Question 2

What is the amperage range typically used for GTAW of 3 mm (1/8-inch) stainless steel with a 2.4 mm tungsten electrode?

Accepted Answer

70–110 A DCEN

Answer

For 3 mm stainless steel with a 2.4 mm tungsten on DCEN, a typical range of 70–110 A provides adequate fusion without burn-through. A common rule of thumb is approximately 1 A per 0.025 mm (0.001 inch) of base metal thickness, adjusted for material type, joint configuration, and position.

Question 3

What is 'arc wander' in GTAW and what causes it?

Accepted Answer

Erratic movement of the arc, often caused by a contaminated tungsten tip, improper grinding, or magnetic fields

Answer

Arc wander is uncontrolled deflection or movement of the GTAW arc away from the intended location. Primary causes include a contaminated or improperly shaped tungsten (especially spiral grinding marks), tungsten contaminated by base metal contact, or arc blow from magnetic fields in ferromagnetic workpieces. Replacing or re-grinding the tungsten usually resolves the problem.

Question 4

What is the purpose of pre-flow and post-flow shielding gas in GTAW?

Accepted Answer

Pre-flow purges air from the torch before arc start; post-flow shields the weld and tungsten as they cool after arc stop

Answer

Pre-flow establishes the shielding gas blanket before the arc is struck, preventing air from being present at arc initiation. Post-flow continues shielding gas after the arc is extinguished, protecting the hot tungsten and weld metal from oxidation as they cool. Post-flow time should be sufficient to cool the tungsten to below its oxidation temperature (approximately 5–15 seconds depending on current and electrode size).

Question 5

What type of joint preparation is typically used for GTAW butt welding of 6 mm stainless steel pipe (schedule 40)?

Accepted Answer

37.5° bevel with a 1.5 mm root face and 2.5 mm root opening (60° included angle V-groove with open root)

Answer

For GTAW root pass welding of stainless steel pipe, a 37.5° bevel per side (75° included angle) with a 1.5–2.0 mm root face and approximately 2.5 mm root opening is standard. This allows the root pass to be made with the keyhole technique for complete penetration. The exact dimensions are specified in the WPS.

Red Seal Welder 456A Practice Test

Red Seal Welder 456A Practice Test

456A TIG (GTAW - Gas Tungsten Arc Welding) 4