How is preheat temperature established in the field and what tools are used to measure it?

• A. Preheat temperature is specified by WPS or code; measured with thermocouples or infrared thermometers; adjust until target temperature achieved.
• B. Preheat temp chosen arbitrarily; measured with a ruler.
• C. Preheat temp not required; measured with a stethoscope.
• D. Preheat temperature determined after welding.

Answer: (A)

Preheat temperature is set by the welding procedure specification (WPS) or the applicable code, and the actual temperature is verified in the field with temperature-measuring tools. You’ll typically use a thermocouple attached to the base metal near the joint to read the surface temperature, or a non-contact infrared thermometer for a quick reading, keeping in mind factors like emissivity and coatings for accurate results. If the reading isn’t at the target, you increase preheating until it is, then begin welding. This ensures proper hydrogen control and reduces cracking risks by bringing the metal to the correct temperature before welding. The other ideas—choosing a temperature arbitrarily, using a ruler or stethoscope, or setting the temperature after welding—don’t provide reliable, code-compliant verification.