Question 1

What are the consequences of exceeding the maximum heat input?

Accepted Answer

Excessive heat input causes: (1) grain coarsening in the HAZ, reducing toughness (Charpy impact values drop significantly), (2) increased distortion and residual stress, (3) wider HAZ with degraded properties, (4) risk of hot cracking in susceptible alloys, (5) potential violation of code requirements (AWS D1.1 limits heat input for prequalified WPSs). For quenched and tempered steels, excessive heat can soften the HAZ below minimum specified hardness.

Question 2

When is preheat required and how is the temperature determined?

Accepted Answer

Preheat is required when CE > 0.45 (IIW formula), material thickness > 25 mm, or the ambient temperature is below 5°C. Minimum preheat temperature is calculated using EN 1011-2 or AWS D1.1 guidelines based on CE, thickness, hydrogen level, and heat input. Typical values: 75°C for CE=0.45 in 25 mm plate, up to 200°C for high-CE steels. Preheat must be applied uniformly over at least 75 mm on each side of the joint.