CWI Welding Process Fundamentals 4 — Questions and Answers
Question 1: What is the primary reason low-hydrogen electrodes must be stored in a rod oven?
- To increase their electrical conductivity
- To prevent moisture absorption, which can introduce hydrogen into the weld and cause cracking (Correct answer)
- To soften the coating for easier striking
- To maintain their flux color for identification
Correct answer: To prevent moisture absorption, which can introduce hydrogen into the weld and cause cracking
Low-hydrogen electrode coatings readily absorb atmospheric moisture; hydrogen from this moisture dissolves in the weld pool and can cause hydrogen-induced (cold) cracking.
Question 2: In electroslag welding (ESW), the primary heat source for melting is:
- The arc between the electrode and base metal
- Resistance heating as current passes through the molten slag pool (Correct answer)
- A laser beam focused on the joint
- Induction heating coils surrounding the joint
Correct answer: Resistance heating as current passes through the molten slag pool
ESW is not an arc process; once started, heat is generated by electrical resistance in the conductive molten slag pool through which the welding current passes.
Question 3: What does 'arc blow' refer to in SMAW welding?
- Spattering caused by excessive amperage
- Deflection of the arc from its intended path due to magnetic forces in the workpiece (Correct answer)
- A puff of smoke caused by coated electrode burning
- Incomplete fusion caused by too fast a travel speed
Correct answer: Deflection of the arc from its intended path due to magnetic forces in the workpiece
Arc blow occurs when stray magnetic fields in the base metal deflect the welding arc forward or backward, making it difficult to control the weld pool.
Question 4: Which of the following base metal conditions most increases the risk of hydrogen-induced cracking (HIC)?
- High preheat temperature
- High carbon equivalent and high restraint (Correct answer)
- Low alloy content and thin section
- Post-weld heat treatment applied immediately after welding
Correct answer: High carbon equivalent and high restraint
HIC risk increases with higher carbon equivalent (hardness), high hydrogen levels in the weld, and high restraint that prevents stress relief during cooling.
Question 5: What is the purpose of a 'backing bar' in groove weld preparation?
- To preheat the base metal before welding
- To support the root pass and prevent burn-through, ensuring full penetration (Correct answer)
- To measure the root opening before welding
- To control interpass temperature
Correct answer: To support the root pass and prevent burn-through, ensuring full penetration
A backing bar (backing strip) placed behind the root provides support for the first weld pass, allowing the welder to achieve full penetration without burning through.
Question 6: In resistance spot welding (RSW), the weld nugget forms primarily due to:
- Filler metal melted between the electrodes
- Heat generated by electrical resistance at the faying surfaces as current passes through (Correct answer)
- Friction between the two electrodes pressing the sheets together
- A shielding gas reaction between the sheets
Correct answer: Heat generated by electrical resistance at the faying surfaces as current passes through
In RSW, the highest resistance at the interface between the two workpieces generates concentrated heat that melts and fuses the metal into a nugget under electrode pressure.
Question 7: What is meant by 'weld metal dilution' in a cladding or overlay application?
- The percentage of flux consumed relative to wire melted
- The proportion of base metal melted and mixed into the deposited weld metal (Correct answer)
- The reduction in weld bead width due to high travel speed
- The loss of alloying elements during multi-pass welding
Correct answer: The proportion of base metal melted and mixed into the deposited weld metal
Dilution is the percentage of base metal mixed into the weld deposit; high dilution in overlay applications can degrade the chemical composition and corrosion resistance of the cladding layer.
CWI Welding Process Fundamentals 4
What is the primary reason low-hydrogen electrodes must be stored in a rod oven?