Weld Crack Prevention Tool
An educational guide to understanding the main types of weld cracks and the primary strategies used to prevent them.
Weld Cracking: The Ultimate Failure
A crack is the most severe type of welding defect. Unlike porosity or undercut, which might be acceptable in some non-critical applications, a crack is almost always a cause for rejection. Cracks act as significant stress risers and can lead to catastrophic failure of a structure. Understanding their causes is the first step to prevention.
Hydrogen-Induced Cracking
Also known as cold cracking, this is a delayed crack that can appear hours or even days after welding. It requires three things to occur: a susceptible (hard) microstructure, the presence of hydrogen, and high stress. Removing any one of these three factors will prevent the crack.
Solidification Cracking
Also known as hot cracking, this occurs as the weld metal is solidifying (cooling). It typically happens in the center of the weld. It's caused by impurities in the weld metal (like sulfur and phosphorus) that have a low melting point. These impurities get pushed to the center and are the last to solidify, creating a weak film that is pulled apart by shrinkage stresses.
Liquation Cracking
This is a micro-crack that occurs in the Heat-Affected Zone (HAZ) just outside the weld, not in the weld metal itself. It happens when low-melting-point phases along the grain boundaries of the base metal are melted (liquated) by the heat of welding. As the weld cools and shrinks, it pulls these weakened boundaries apart.