CWI Welding Process Fundamentals 3 — Questions and Answers
Question 1: What is 'porosity' in a weld and what commonly causes it?
- Surface cracks caused by rapid cooling
- Gas pockets trapped in the solidifying weld metal, often from contamination or moisture (Correct answer)
- Incomplete fusion between weld passes
- Excessive reinforcement on the weld face
Correct answer: Gas pockets trapped in the solidifying weld metal, often from contamination or moisture
Porosity results from gases (hydrogen, oxygen, nitrogen) becoming trapped as the weld pool solidifies, commonly caused by moisture, contamination, or inadequate shielding.
Question 2: Which electrode designation is a low-hydrogen SMAW electrode?
- E6010
- E6013
- E7018 (Correct answer)
- E6011
Correct answer: E7018
E7018 has a low-hydrogen iron powder coating (indicated by the '8' suffix), requiring storage in a rod oven to prevent moisture absorption.
Question 3: What does 'undercutting' refer to in welding inspection?
- A groove melted into the base metal at the weld toe that is not filled by weld metal (Correct answer)
- Insufficient throat on a fillet weld
- Overlap of weld metal beyond the weld toe
- A crack running parallel to the weld axis
Correct answer: A groove melted into the base metal at the weld toe that is not filled by weld metal
Undercut is a groove or channel burned into the base metal along the weld toes or root that weakens the joint by reducing cross-sectional area.
Question 4: In plasma arc welding (PAW), what distinguishes the 'keyhole' technique from conventional welding?
- It uses a lower amperage than GTAW
- A focused plasma jet penetrates completely through the base metal, creating a hole that is filled as the torch progresses (Correct answer)
- It deposits filler metal from a rotating electrode
- It uses alternating current to clean aluminum oxide
Correct answer: A focused plasma jet penetrates completely through the base metal, creating a hole that is filled as the torch progresses
The keyhole technique in PAW uses a constricted, high-energy plasma column to pierce through the workpiece; the molten metal flows around and behind, producing full-penetration welds in one pass.
Question 5: What is the significance of the 'interpass temperature' in multi-pass welding?
- It is the temperature of the preheat flame before welding begins
- It is the maximum temperature of the weld area between passes, controlled to prevent metallurgical damage (Correct answer)
- It defines the cooling rate after the final pass
- It measures the temperature of the shielding gas
Correct answer: It is the maximum temperature of the weld area between passes, controlled to prevent metallurgical damage
Interpass temperature is the maximum allowed temperature of the weld zone before depositing the next pass, preventing excessive heat input that can degrade toughness and mechanical properties.
Question 6: Which welding position is designated as '5G' in the AWS classification system?
- Flat position on a groove weld
- Pipe welded with its axis vertical and rotated during welding
- Pipe welded with its axis horizontal and fixed (not rotated) (Correct answer)
- Overhead groove weld on plate
Correct answer: Pipe welded with its axis horizontal and fixed (not rotated)
5G designates pipe with its axis horizontal and the pipe fixed in place, requiring the welder to weld in all positions (flat, vertical, and overhead) around the pipe.
Question 7: What is 'cold lap' (overlap) in welding?
- A weld made at temperatures below the recommended preheat
- Weld metal that extends beyond the weld toe and lies on the base metal without fusion (Correct answer)
- Incomplete root penetration on a groove weld
- A crack in the heat-affected zone caused by hydrogen
Correct answer: Weld metal that extends beyond the weld toe and lies on the base metal without fusion
Overlap (cold lap) occurs when weld metal rolls over onto the base metal surface without fusing to it, creating a mechanical notch that can initiate fatigue cracks.
CWI Welding Process Fundamentals 3
What is 'porosity' in a weld and what commonly causes it?