A CWI is inspecting a weldment that requires a specific preheat temperature of 200°F (93°C) according to the WPS. The CWI uses a temperature indicating crayon to verify the preheat. Which of the following is the most appropriate technique for applying and observing the crayon?
- ADraw a continuous line directly on the joint preparation area, ensuring it melts immediately upon application.
- BApply the crayon to a separate test coupon heated alongside the weldment, observing its melt behavior.
- CMark the base metal approximately 1 inch (25 mm) from the weld joint, and observe the mark melt as the temperature is reached.
- DMark the base metal 6 inches (150 mm) from the weld joint and ensure the mark remains solid, indicating temperature below 200°F.
Show answer & explanationAnswer & explanation
Correct answer: C. Mark the base metal approximately 1 inch (25 mm) from the weld joint, and observe the mark melt as the temperature is reached.
Temperature indicating crayons are designed to melt at a specific temperature. The correct technique is to mark the base metal adjacent to the weld joint (typically 1-3 inches away, depending on thickness) and observe when that mark melts. This indicates the base metal has reached at least the crayon's rated temperature. Marking directly on the joint can contaminate it, and marking too far away may not reflect the actual preheat of the weld area.
Why the other options are wrong
- A. Drawing a continuous line directly on the joint can contaminate the weld area, and 'melting immediately upon application' doesn't ensure the *entire* area is at temperature, or that it wasn't already too hot.
- B. Using a separate test coupon is not standard practice for verifying preheat on the actual weldment and may not accurately reflect its temperature.
- D. Marking 6 inches away is often too far to accurately represent the preheat temperature of the immediate weld zone. Observing it remain solid indicates it's *below* 200°F, which is not what the CWI wants for verification of *reaching* 200°F.
Preheat Verification (Crayon)
Preheat temperature is verified using temperature-indicating crayons by observing their melt behavior on the base metal adjacent to the weld joint, ensuring the specified minimum temperature is reached.
- Crayon melts at a specific temperature.
- Apply 1-3 inches from weld joint.
- Observe the crayon melt to confirm minimum temperature.
- Avoid contaminating joint with crayon.
Memory trick: Mark 'N' melt 'N'ear the 'N'eck of the weld.