Welding Hot Cracks

Hot cracks (also called solidification or liquation cracking) are among the most dangerous welding defects. They form at high temperatures, near the solidus, when the weld is still partially molten and extremely brittle.

♦ Where do they occur?

·Weld Metal → Solidification cracking (centerline of bead).

·HAZ → Liquation cracking (partially melted zone).

♦ Why and when do they happen?

·Lack of ductility at high temperature.

·Impurities (S & P) segregating at grain boundaries.

·Tensile stresses from weld contraction.

·Hot cracks form at high temperatures near the solidus, typically during the  final stages of weld solidification.

♦ The Phenomenon:

- Caused by solidification shrinkage stresses acting on weak grain boundaries.

- Exacerbated by low-melting impurities (S, P) that segregate during cooling.

-Typically appear along the weld centerline or crater ends.

♦ Materials Affected:

- Carbon & low-alloy steels

-  Austenitic stainless steels

-  Nickel alloys

-  Aluminum alloys

♦ Challenges:

- Difficult to detect visually → can remain hidden inside welds.

- Leads to catastrophic failures in offshore, pipelines, pressure vessels, aerospace, and bridges.

- Compromises safety, compliance, and durability.

♦ How to Avoid Hot Cracks:

√ Control heat input → avoid excessive penetration & wide beads.

√ Use filler metals designed for crack resistance (ferrite-controlled in stainless, Mn-rich in fully austenitic steels).

√ Ensure good weld sequence & restraint control to minimize residual stresses.

√ Maintain low impurity levels (S & P) in materials and consumables.

√ Use proper groove design to improve width-to-depth ratio.

♦Why it matters for industry:

 - Offshore & pipelines → catastrophic leaks.

 - Pressure vessels → safety compliance risk.

 - Aerospace & cryogenics → hidden cracks = severe failure risk.

 - Bridges & infrastructure → long-term durability loss.

♦ Key Takeaways:

√ Hot cracks form when the weld is at its weakest state.

√ They are preventable with the right material, consumables, design, and parameters.

√ Proactive control is essential to ensure safety, reliability, and long-term durability.