Execution of FCAW Welds and Welding Procedure Compliance
This domain is about running the bead inside the qualified envelope: following the WPS, controlling heat input, and keeping the technique consistent enough that inspection passes first time.
Pre-arc checks
Read the WPS: process, consumable classification, polarity, current range, voltage range, travel speed, preheat and interpass temperature, position, and whether stringer or weave beads are permitted. Check the consumable certificate and that the spool is dry. Measure preheat on the thicker member.
Technique
FCAW gas-shielded is normally run with a drag angle of about 5–15°, holding the wire at the leading edge of the puddle. Keep weave width within the WPS limit (often three times the electrode diameter) because wide weaving lowers penetration at the sides. Clean slag between passes - FCAW slag is thin and glassy and easy to leave behind at the toes. Use backstep or balanced sequences on long joints.
Heat input
Heat input (kJ/in) = (volts × amps × 60) ÷ (travel speed in ipm × 1000).
Worked example
WPS allows a maximum of 45 kJ/in. The welder runs 26 V, 220 A at 8 ipm. Calculation: (26 × 220 × 60) ÷ (8 × 1000) = 343,200 ÷ 8,000 = 42.9 kJ/in, which complies. If travel speed falls to 6 ipm the result becomes 57.2 kJ/in, exceeding the maximum. Reasoning: heat input is inversely proportional to travel speed, so slowing down to "get penetration" can breach the procedure and change toughness.
Traps that cost marks
Trusting an uncalibrated ammeter. Estimating travel speed by eye instead of measuring a timed length. Substituting a different gas mix or wire classification. Skipping preheat on thick sections. Weaving beyond the WPS limit.