A structural steel fabricator is using FCAW-S (E71T-8 wire) to weld heavy sections of structural steel in an outdoor environment without windbreaks. The welding procedure specifies a minimum interpass temperature of 150°C (300°F). After welding a 25 mm (1 in.) thick fillet weld, magnetic particle inspection reveals underbead cracking. Assuming proper joint preparation, current, and voltage settings, what is the most likely contributing factor to this defect?

Question: A structural steel fabricator is using FCAW-S (E71T-8 wire) to weld heavy sections of structural steel in an outdoor environment without windbreaks. The welding procedure specifies a minimum interpass temperature of 150°C (300°F). After welding a 25 mm (1 in.) thick fillet weld, magnetic particle inspection reveals underbead cracking. Assuming proper joint preparation, current, and voltage settings, what is the most likely contributing factor to this defect?

Answer options:

• Inadequate cleaning of the base metal before welding
• Insufficient electrode stick-out during welding ✅ Rapid cooling of the weldment caused by environmental conditions
• Using a wire with insufficient tensile strength for the application

Correct answer: Rapid cooling of the weldment caused by environmental conditions

Explanation: Underbead cracking (or hydrogen-induced cracking) in heavier sections, particularly in an outdoor environment, is often exacerbated by rapid cooling rates which prevent hydrogen from diffusing out of the weld. While inadequate preheat would directly contribute to this, rapid cooling of the weldment itself, even with initial preheat, can be a major factor. Inadequate cleaning would more likely cause porosity, insufficient stick-out would cause arc instability or lack of penetration, and tensile strength issues relate to mechanical properties, not typically directly to underbead cracking in this scenario.