SAW Flux Types & Wire Selection 2 — Questions and Answers
Question 1: What effect does increasing arc voltage have on SAW weld bead geometry?
- Increases penetration and decreases bead width
- Increases bead width and decreases penetration (Correct answer)
- Decreases both bead width and penetration equally
- Has no effect on bead geometry, only on travel speed
Correct answer: Increases bead width and decreases penetration
Higher arc voltage lengthens the arc column, spreading heat laterally to produce a wider, flatter bead with reduced depth of fusion into the base metal.
Question 2: When selecting SAW wire for low-alloy high-strength steel, what is the primary consideration for maintaining weld metal toughness?
- Maximizing silicon content in the wire for better fluidity
- Controlling carbon equivalent and matching alloy additions (Ni, Mo) to base metal requirements (Correct answer)
- Using the largest diameter wire available for higher heat input
- Selecting the highest basicity flux regardless of wire chemistry
Correct answer: Controlling carbon equivalent and matching alloy additions (Ni, Mo) to base metal requirements
Weld metal toughness on high-strength steels depends on controlled carbon equivalent and appropriate alloy additions; the wire chemistry must be matched to the required mechanical properties.
Question 3: In a tandem SAW setup, what is the typical polarity arrangement for lead and trail electrodes?
- Both DCEP to maximize penetration on both wires
- Lead electrode DCEP for penetration; trail electrode DCEN or AC for deposition (Correct answer)
- Both DCEN to maximize deposition rate
- Both AC at the same phase angle
Correct answer: Lead electrode DCEP for penetration; trail electrode DCEN or AC for deposition
Tandem SAW optimizes each wire independently: the lead wire uses DCEP for deep penetration to achieve fusion, while the trail wire uses DCEN or AC to maximize deposition rate and shape the bead.
Question 4: Compared to DCEP (electrode positive), using DCEN (electrode negative) polarity in SAW produces:
- Higher penetration and lower deposition rate
- Lower penetration and higher deposition rate (Correct answer)
- Identical penetration and deposition as DCEP
- Higher heat input to the base metal with equal deposition
Correct answer: Lower penetration and higher deposition rate
With DCEN, more heat is generated at the electrode tip rather than the base metal, melting more wire per unit time (higher deposition) while reducing fusion depth (lower penetration).
Question 5: In the AWS A5.17 flux-wire classification 'F7A2-EM12K', what does the 'F7' prefix indicate about the weld deposit?
- Minimum tensile strength of 60,000 psi (60 ksi)
- Minimum tensile strength of 70,000 psi (70 ksi) (Correct answer)
- Minimum tensile strength of 80,000 psi (80 ksi)
- Minimum tensile strength of 72,000 psi (72 ksi)
Correct answer: Minimum tensile strength of 70,000 psi (70 ksi)
In AWS A5.17, 'F7' designates a flux that, when used with the specified wire, produces weld metal with a minimum 70,000 psi tensile strength; the number represents tensile strength in multiples of 10,000 psi.
Question 6: What does the 'A2' designator in the AWS A5.17 classification 'F7A2-EM12K' specify?
- Two-pass welding technique is required for qualification
- As-welded condition with minimum 20 ft-lb CVN impact toughness at −20°F (Correct answer)
- 2% alloy content limit in the wire electrode
- Second revision of the A5.17 standard applies
Correct answer: As-welded condition with minimum 20 ft-lb CVN impact toughness at −20°F
'A' indicates the as-welded condition (no post-weld heat treatment), and '2' specifies the Charpy V-Notch test temperature as −20°F with a minimum 20 ft-lb impact requirement.
Question 7: Why is controlling electrode extension (contact-tip-to-work distance) important in SAW welding?
- Longer extension increases flux layer depth automatically
- Extension affects resistive preheating of the wire, altering deposition rate and arc current (Correct answer)
- Extension determines which flux type must be used
- Extension has no measurable effect on SAW weld quality
Correct answer: Extension affects resistive preheating of the wire, altering deposition rate and arc current
The wire between the contact tip and the arc acts as a resistor; longer extension increases resistive heating, which raises deposition rate but reduces current for the same wire feed speed, altering penetration.
SAW Flux Types & Wire Selection 2
What effect does increasing arc voltage have on SAW weld bead geometry?