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Welder Red Seal · Question

A welder is tasked with repairing a structural frame made of ASTM A36 carbon steel. The ambient temperature in the shop is 15 °C. The repair involves a fillet weld using the Shielded Metal Arc Welding (SMAW) process. What preheat temperature range, if any, is generally recommended for this application?

For ASTM A36 carbon steel, which is a low-carbon steel, a preheat of 50 °C to 75 °C is often recommended for welding sections thicker than about 20 mm, or when

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Question: A welder is tasked with repairing a structural frame made of ASTM A36 carbon steel. The ambient temperature in the shop is 15 °C. The repair involves a fillet weld using the Shielded Metal Arc Welding (SMAW) process. What preheat temperature range, if any, is generally recommended for this application?

Answer options:

  • No preheat required ✅ 50 °C to 75 °C
  • 100 °C to 120 °C
  • 150 °C to 200 °C

Correct answer: 50 °C to 75 °C

Explanation: For ASTM A36 carbon steel, which is a low-carbon steel, a preheat of 50 °C to 75 °C is often recommended for welding sections thicker than about 20 mm, or when the ambient temperature is below 0 °C, to reduce hydrogen-induced cracking and improve weldability. While no preheat might be acceptable for very thin sections in warm conditions, a slight preheat is a good practice for structural repairs to ensure optimal weld quality.

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