456A SMAW (Shielded Metal Arc Welding) 4 — Questions and Answers
Question 1: Which electrode classification would be most appropriate for welding A516 Grade 70 pressure vessel steel with SMAW?
- E7016 or E7018 (Correct answer)
- E6010
- E6012
- E7024
Correct answer: E7016 or E7018
E7016 or E7018 low-hydrogen electrodes are the standard choice for pressure vessel steels such as A516 Gr 70 because they provide low hydrogen content (preventing HIC), matching tensile strength (~70 ksi/480 MPa), and good toughness. E6010 can be used for root passes.
Question 2: What is 'slag inclusion' in a SMAW weld and what is the primary prevention method?
- Slag trapped in the weld metal; prevented by thorough inter-pass slag removal and proper technique (Correct answer)
- Gas bubbles trapped during solidification; prevented by drying electrodes
- Cold lap at the weld toe; prevented by increasing amperage
- Undissolved flux at the root; prevented by using smaller electrodes
Correct answer: Slag trapped in the weld metal; prevented by thorough inter-pass slag removal and proper technique
Slag inclusion occurs when solidified flux (slag) becomes trapped within the weld metal during multi-pass welding. Prevention includes thorough chipping and wire brushing between passes, maintaining proper electrode angle to keep the slag behind the weld pool, and using adequate amperage.
Question 3: What does 'burn-through' mean and what is the most likely cause in SMAW on thin material?
- Complete melting through the base metal; caused by excessive amperage or slow travel speed (Correct answer)
- Oxidation of the weld surface; caused by lack of shielding
- Electrode sticking; caused by insufficient amperage
- Undercut at the root; caused by incorrect joint preparation
Correct answer: Complete melting through the base metal; caused by excessive amperage or slow travel speed
Burn-through is when the arc completely melts through the base metal, creating a hole. On thin material, it is most commonly caused by excessive amperage, too slow a travel speed, or excessive dwell time in one area. Reducing amperage and increasing travel speed are the primary remedies.
Question 4: In SMAW welding of pipe in the 6G position, what does the '6G' designation mean?
- Pipe axis at 45° to horizontal, pipe fixed (not rotated) (Correct answer)
- Pipe axis horizontal, pipe rotated during welding
- Pipe axis vertical, pipe fixed
- Pipe axis at 45°, pipe rotated during welding
Correct answer: Pipe axis at 45° to horizontal, pipe fixed (not rotated)
The 6G position has the pipe axis fixed at 45° to the horizontal. Because the pipe is not rotated, the welder must weld in all positions (flat, vertical, overhead) in a single joint, making it the most demanding qualification test position.
Question 5: What is 'overlap' (cold lap) as a weld discontinuity in SMAW?
- Weld metal that extends beyond the weld toe onto the base metal without fusing to it (Correct answer)
- Weld metal deposited over a previous pass before it cools
- A gap between the end of one electrode run and the start of the next
- Excess weld reinforcement above the base metal surface
Correct answer: Weld metal that extends beyond the weld toe onto the base metal without fusing to it
Overlap (cold lap) occurs when molten weld metal rolls over the toe of the weld and solidifies on the base metal without fusing to it. It is caused by too low an amperage, incorrect electrode angle, or too slow a travel speed. It creates a notch effect and is a rejectable defect.
Question 6: When welding dissimilar metals with SMAW, what is the general rule for electrode selection?
- Select an electrode that matches or slightly undermatches the lower-strength base metal (Correct answer)
- Always use the highest-strength electrode available
- Match the electrode to the higher-strength base metal
- Dissimilar metal welding is not permitted with SMAW
Correct answer: Select an electrode that matches or slightly undermatches the lower-strength base metal
When joining dissimilar strength metals, it is generally recommended to use an electrode that matches or slightly undermatches (undermatch) the weaker of the two base metals. This prevents a brittle transition and allows the joint to deform in the weaker material rather than failing catastrophically at the weld.
456A SMAW (Shielded Metal Arc Welding) 4
Which electrode classification would be most appropriate for welding A516 Grade 70 pressure vessel steel with SMAW?