Hydrogen Cold Cracking (HCC)
Definition
Delayed intergranular cracking in the heat-affected zone or weld metal, caused by atomic hydrogen absorbed during welding, susceptible martensite microstructure, and residual tensile stress. Can occur hours to days post-weld.
- Location
- Heat-affected zone or weld metal
- Contributing factors
- Absorbed hydrogen, susceptible martensite, residual tensile stress
- Onset
- Delayed, hours to days after welding
- Crack path
- Intergranular
Common questions
Why is the delayed onset of hydrogen cold cracking significant for failure investigation?+
Because cracking can appear well after the weld has cooled and passed initial visual inspection, a component can be put into service and fail later, which means investigators need to establish the weld's thermal and hydrogen exposure history, not just examine the final fracture, to confirm HCC as the mechanism.
What welding practices are used to prevent hydrogen cold cracking?+
Common preventive measures include preheating the base metal, using low-hydrogen electrodes or filler metal, controlling interpass temperature, and applying post-weld heat treatment or a hydrogen bake-out to allow absorbed hydrogen to diffuse out before the weld cools to a susceptible microstructure.
How would an investigator distinguish HCC from a weld defect present since fabrication?+
HCC characteristically shows an intergranular fracture surface and originates in the heat-affected zone with evidence consistent with delayed cracking, such as no correlation with the original weld inspection record, whereas a fabrication defect like porosity or lack of fusion is typically identifiable in as-welded radiographic or visual inspection records.
Related terms
- Hot Cracking
- Solidification cracking or liquation cracking that occurs at elevated temperature during or just after welding. Driven by liquid films of low-melting impurity...
- Lack of Fusion (LOF)
- A planar weld defect where the weld metal fails to fuse to the base metal or to the adjacent weld pass. Essentially...
- Laminar Tearing
- Step-like fracture in the base plate beneath a restrained weld, propagating along planes of MnS inclusion stringers aligned with the rolling direction...
- Phased-Array Ultrasonic Testing (PAUT)
- Advanced ultrasonic inspection using a multi-element probe whose beam angle and focal depth are electronically controlled to scan a weld volume systematically....
- Porosity
- Gas-filled voids in weld metal or castings, spherical or elongated (wormhole/piping), caused by dissolved gas evolving during solidification. Reduces cross-section and acts...