456A SMAW (Shielded Metal Arc Welding) 3 — Questions and Answers
Question 1: What is the purpose of preheating before SMAW welding on high-carbon steel?
- To reduce the cooling rate and prevent hydrogen-induced cracking (Correct answer)
- To clean the base metal surface
- To increase the deposition rate
- To improve arc stability
Correct answer: To reduce the cooling rate and prevent hydrogen-induced cracking
Preheating slows the cooling rate of the weld and heat-affected zone (HAZ), which reduces the risk of martensite formation and hydrogen-induced cracking. It also allows hydrogen time to diffuse out of the weld area before cracking can occur.
Question 2: In SMAW, what is 'undercut' and what typically causes it?
- A groove melted into the base metal along the weld toe, caused by excessive amperage or incorrect electrode angle (Correct answer)
- Incomplete penetration through the root of the joint
- A crack along the centerline of the weld bead
- Slag inclusions below the weld surface
Correct answer: A groove melted into the base metal along the weld toe, caused by excessive amperage or incorrect electrode angle
Undercut is a groove or channel melted into the base metal at the weld toe that is not filled by weld metal. It is caused by excessive current, incorrect electrode angle, or too fast a travel speed. Undercut reduces the cross-sectional thickness and acts as a stress riser.
Question 3: What is the significance of the 'H4' or 'H8' suffix on a low-hydrogen electrode designation such as E7018-H4?
- The maximum diffusible hydrogen content in mL per 100g of deposited weld metal (Correct answer)
- The minimum preheat temperature required in hundreds of degrees
- The electrode coating thickness in tenths of a millimetre
- The required holding temperature in the storage oven
Correct answer: The maximum diffusible hydrogen content in mL per 100g of deposited weld metal
The H-designator indicates the maximum diffusible hydrogen content: H4 means ≤4 mL/100g, H8 means ≤8 mL/100g, and H16 means ≤16 mL/100g. Lower hydrogen content reduces the risk of hydrogen-induced cracking.
Question 4: When making multiple passes in a groove weld, what is the purpose of the stringer bead technique compared to weaving?
- Stringer beads minimize heat input and HAZ size, providing better mechanical properties in high-restraint joints (Correct answer)
- Weaving always produces stronger welds than stringer beads
- Stringer beads are only used for flat position welding
- Weaving reduces the number of passes required and improves fusion
Correct answer: Stringer beads minimize heat input and HAZ size, providing better mechanical properties in high-restraint joints
Stringer beads involve minimal side-to-side motion and result in lower heat input per pass. This reduces HAZ size, minimizes distortion, and is preferred for high-strength or hardenable steels. Many WPS documents specify stringer beads to control heat input.
Question 5: What does the term 'deposition rate' refer to in SMAW welding?
- The weight of weld metal deposited per unit of time (kg/hr) (Correct answer)
- The number of electrode sticks consumed per hour
- The travel speed of the electrode along the joint
- The ratio of weld metal to slag produced
Correct answer: The weight of weld metal deposited per unit of time (kg/hr)
Deposition rate is the weight of weld metal deposited per unit of time, expressed in kg/hr or lb/hr. It is affected by amperage, electrode diameter, electrode type, and welding position. Higher deposition rates increase productivity.
Question 6: What is the correct way to handle and store E7018 electrodes on a jobsite according to CSA W48 requirements?
- Keep in a heated rod oven at 120–150°C; once removed, use within 4 hours or return to oven for reconditioning (Correct answer)
- Store in original sealed container at room temperature; open only when ready to use
- Electrodes can be left in the open for up to 8 hours before moisture becomes a concern
- Reconditioning is not permitted — discard any electrodes exposed to humidity
Correct answer: Keep in a heated rod oven at 120–150°C; once removed, use within 4 hours or return to oven for reconditioning
CSA W48 specifies that low-hydrogen electrodes must be stored in holding ovens at 120–150°C. After removal, they should be used within 4 hours (or as specified by the WPS). Electrodes can be reconditioned (rebaked) a limited number of times if they have been exposed to moisture.
456A SMAW (Shielded Metal Arc Welding) 3
What is the purpose of preheating before SMAW welding on high-carbon steel?