AWS Certified Welding Inspector — FundamentalsInspector Duties and ResponsibilitiesMedium
During a multi-pass groove weld inspection on a critical pressure vessel, a CWI observes that the welder is consistently exceeding the maximum interpass temperature specified in the Welding Procedure Specification (WPS) by 50°F (28°C). The WPS mandates a maximum interpass temperature of 350°F (177°C). What is the primary concern associated with exceeding the maximum interpass temperature in this scenario?
- ADegradation of mechanical properties, particularly toughness, in the heat-affected zone (HAZ).
- BIncreased risk of hydrogen-induced cracking in the weld metal.
- CReduced tensile strength and increased hardness of the weld.
- DFormation of excessive slag and porosity within the weld bead.
Show answer & explanationAnswer & explanation
Correct answer: A. Degradation of mechanical properties, particularly toughness, in the heat-affected zone (HAZ).
Exceeding the maximum interpass temperature can lead to slower cooling rates, which can coarsen the grain structure and negatively impact the mechanical properties, especially toughness, in the Heat-Affected Zone (HAZ) and weld metal. This is particularly critical for pressure vessels.
Why the other options are wrong
- B. Hydrogen-induced cracking is more associated with rapid cooling rates, not excessively high interpass temperatures.
- C. While properties can change, reduced toughness in the HAZ is a more direct and critical consequence of high interpass temperatures.
- D. Excessive slag and porosity are typically related to welding technique, shielding gas, or consumable issues, not directly to high interpass temperature.
Maximum Interpass Temperature Effects
The highest temperature allowed on a weld pass before the next pass is deposited. Exceeding it can negatively affect the mechanical properties, particularly toughness, of the weld and HAZ by altering cooling rates and grain structure.
- Crucial for controlling cooling rates.
- Impacts grain structure and mechanical properties.
- Essential for steels susceptible to HAZ embrittlement.
Memory trick: Too hot, too slow, toughness low.