Possible Causes of Weld Cracking:

The image shows a longitudinal crack along the centerline of a weld bead on a cylindrical pipe. This type of defect is commonly referred to as a weld crack. Based on the appearance, here are the possible reasons:

Possible Causes of Weld Cracking:

1. Hot Cracking (Solidification Cracking)

Occurs during cooling and solidification of the weld metal.

Caused by:

High restraint (rigid joints)

Improper filler material

High sulfur or phosphorus in base/weld metal

Poor weld bead shape (excessive concavity or convexity)

2. Cold Cracking (Hydrogen-Induced Cracking)

Occurs after the weld has cooled to ambient temperature.

Caused by:

High hydrogen levels (from moisture in electrodes, flux, or base metal)

High residual stress

Hard microstructures like martensite in the heat-affected zone (HAZ)

Common in carbon and low alloy steels.

3. Lack of Preheat or Post-Weld Heat Treatment (PWHT)

Failure to preheat thick or high-carbon materials leads to rapid cooling, causing cracking.

Absence of PWHT in sensitive materials increases risk of delayed cracking.

4. Improper Welding Parameters

Excessively high heat input or too low can both cause weld cracking.

Incorrect welding speed.

5. Poor Joint Design or Fit-up

High restraint, poor alignment, or gaps between joint parts.

How to Prevent:

✅ Proper material selection and compatible filler metal.

✅ Preheat when necessary (especially on high carbon steels).

✅ Control hydrogen: use low-hydrogen electrodes, dry consumables.

✅ Optimize heat input.

✅ Apply PWHT if required by the code.

✅ Proper joint preparation and fit-up.