Certified Welder Base Metal Preparation 3 — Questions and Answers
Question 1: Which tool is most appropriate for removing mill scale from a narrow weld groove prior to GTAW on carbon steel?
- Wire brush
- Needle scaler
- Die grinder with carbide burr (Correct answer)
- Angle grinder with flap disc
Correct answer: Die grinder with carbide burr
A die grinder with a carbide burr can reach into tight grooves and remove mill scale without leaving abrasive particles that could contaminate the weld.
Question 2: When performing an oxy-fuel cut on carbon steel plate, the cut edge should be ground before welding primarily to remove:
- Base metal carbon
- Drag lines and hardened surface layer (Correct answer)
- Residual oxygen
- Plate camber
Correct answer: Drag lines and hardened surface layer
Oxy-fuel cutting produces a hardened surface layer from rapid quenching and drag lines that can act as stress risers if not removed prior to welding.
Question 3: Interpass cleaning between weld passes is required mainly to prevent:
- Excessive heat input
- Slag inclusions in the completed weld (Correct answer)
- Base metal distortion
- Undercut along the toes
Correct answer: Slag inclusions in the completed weld
Removing slag between passes prevents slag entrapment, which would appear as inclusions in radiographic or ultrasonic inspection of the finished weld.
Question 4: What is the correct fit-up root opening for a standard single-V butt joint when using SMAW on ¼-inch plate?
- 0 in (closed root)
- 1/16 to 3/32 in (Correct answer)
- 3/16 to ¼ in
- ½ in
Correct answer: 1/16 to 3/32 in
A root opening of 1/16 to 3/32 inch provides adequate access for the electrode to achieve root fusion without excessive melt-through.
Question 5: A welder is preparing aluminum base metal for GTAW. Which preparation step is unique to aluminum compared to steel?
- Degreasing with acetone
- Mechanical removal of the oxide layer immediately before welding (Correct answer)
- Preheating to 300°F
- Using a stainless steel wire brush
Correct answer: Mechanical removal of the oxide layer immediately before welding
Aluminum's oxide layer (Al₂O₃) has a much higher melting point than the base metal and must be freshly removed immediately before welding to prevent oxide inclusions.
Question 6: Which discontinuity is most likely caused by inadequate cleaning of a lap joint surface before welding?
- Underfill
- Incomplete fusion
- Porosity (Correct answer)
- Excessive reinforcement
Correct answer: Porosity
Contaminants such as oil, rust, or moisture on faying surfaces vaporize during welding and become trapped gas pores in the solidifying weld metal.
Question 7: On a T-joint fillet weld, what is the effect of excessive gap between the web and flange members?
- Increased penetration
- Increased required filler metal and potential burn-through (Correct answer)
- Reduced heat input
- Improved fusion at the root
Correct answer: Increased required filler metal and potential burn-through
An excessive gap in a T-joint increases the volume of filler needed and can cause the arc to burn through the root rather than fusing both members.
Certified Welder Base Metal Preparation 3
Which tool is most appropriate for removing mill scale from a narrow weld groove prior to GTAW on carbon steel?