AWS Flux-Cored Arc Welding (FCAW) 2 — Questions and Answers

Question 1: What is the primary difference between FCAW-G and FCAW-S?

FCAW-G uses DC power; FCAW-S uses AC power
FCAW-G uses external shielding gas; FCAW-S is self-shielded via flux in the core (Correct answer)
FCAW-G welds thicker material; FCAW-S welds thinner material
FCAW-G uses solid wire; FCAW-S uses tubular wire

Correct answer: FCAW-G uses external shielding gas; FCAW-S is self-shielded via flux in the core

FCAW-G (gas-shielded) requires an external shielding gas like CO2 or Ar/CO2 mix, while FCAW-S (self-shielded) generates its own shielding from the flux core — no external gas needed.

AWS classifies FCAW electrodes by their shielding method. FCAW-G electrodes (e.g., E71T-1C) require external CO2 or Ar/CO2 shielding gas — suitable for shop work. FCAW-S electrodes (e.g., E71T-11) generate shielding from flux ingredients in the core, making them viable outdoors in windy conditions. FCAW-S typically produces more spatter and slag but eliminates the need for gas cylinders, making it popular for field and structural work.

Question 2: Which AWS electrode classification is used for a flux-cored wire suitable for all-position welding with CO2 shielding gas?

E70T-1C
E71T-1C (Correct answer)
E70T-5C
E71T-11

Correct answer: E71T-1C

E71T-1C: E=electrode, 7=70 ksi tensile, 1=all-position, T=tubular (flux-cored), 1=usability designation, C=CO2 shielding gas.

Per AWS A5.20, FCAW electrode classifications follow the format EXXT-X(gas). The digit after the strength designation: '0' = flat and horizontal only; '1' = all positions. The suffix letter indicates shielding gas type (C=CO2, M=mixed Ar/CO2). E71T-1C is one of the most widely used FCAW electrodes in structural steel fabrication, approved for use with AWS D1.1 structural welding code.

Question 3: Excessive wire extension (stick-out) in FCAW will typically cause:

Increased penetration and wider bead
Undercut along the weld toes
Reduced current, lower heat input, and incomplete fusion (Correct answer)
Increased spatter from excess gas flow

Correct answer: Reduced current, lower heat input, and incomplete fusion

Excessive CTWD (Contact Tip to Work Distance / stick-out) increases resistance in the wire, which reduces current, lowers heat input, and can lead to incomplete fusion or cold lap.

In FCAW with CV (constant voltage) power, increasing stick-out raises the electrical resistance of the wire between the contact tip and the arc. The power source maintains voltage, so current drops. This reduces arc energy, causing shallow penetration, incomplete fusion (cold lap), and a narrow, convex bead. Standard FCAW stick-out is typically 3/4 to 1-1/2 inches depending on electrode diameter. Maintaining correct CTWD is critical for consistent weld quality.

Question 4: Porosity in FCAW welds is most commonly caused by:

Excessive travel speed
Contamination (moisture, rust, oil) or shielding gas disruption (Correct answer)
Too high a voltage setting
Using DC reverse polarity (DCEP)

Correct answer: Contamination (moisture, rust, oil) or shielding gas disruption

Porosity results from gas trapped in the weld pool. Sources include moisture on the base metal or wire, oil/rust contamination, insufficient gas coverage, or wind disturbing the gas shield.

FCAW porosity has several root causes: moisture absorbed by the flux core (improper wire storage), rust or mill scale on the base metal, oil or paint contamination, inadequate shielding gas flow rate, wind blowing away the gas shield (problematic for FCAW-G outdoors), excessive nozzle-to-work distance, or blocked nozzle. AWS D1.1 limits porosity size and distribution. Prevention includes storing wire in dry conditions, cleaning base metal, maintaining proper gas flow (typically 35-50 CFH), and using FCAW-S in outdoor/windy environments.

Question 5: In FCAW, the work angle for a horizontal fillet weld is typically:

0 degrees (parallel to the vertical member)
45 degrees (bisecting the joint angle) (Correct answer)
70–80 degrees from the horizontal plate
90 degrees (perpendicular to travel direction)

Correct answer: 45 degrees (bisecting the joint angle)

For a horizontal fillet weld, the electrode is typically held at 45 degrees (bisecting the angle between horizontal and vertical members), directing the arc into the root of the joint.

AWS welding procedure guidance specifies that for a T-joint fillet weld in the horizontal (2F) position, the work angle should be 45 degrees — bisecting the 90-degree angle between the two plates. This directs the arc energy equally into both members, promoting fusion at the root. A slight variation (40–50 degrees) may be used to counteract gravity effects on the molten pool. Incorrect work angle leads to underfill on one member or overlap on the horizontal plate.

Question 6: Which polarity is standard for most FCAW-G electrodes?

DCEN (straight polarity)
DCEP (reverse polarity) (Correct answer)
AC only
Either polarity — no difference

Correct answer: DCEP (reverse polarity)

Most FCAW-G electrodes require DCEP (electrode positive, reverse polarity) to achieve the proper arc characteristics, penetration, and slag coverage.

DCEP (Direct Current Electrode Positive) directs electron flow from workpiece to electrode. For most FCAW-G electrodes per AWS A5.20, DCEP provides stable arc transfer, good penetration, and proper slag formation. Some self-shielded FCAW-S electrodes (e.g., E71T-11) are designed for DCEN to reduce heat input and improve out-of-position performance. The electrode manufacturer's data sheet and WPS always specify the correct polarity.

AWS Flux-Cored Arc Welding (FCAW) 2

What is the primary difference between FCAW-G and FCAW-S?