Wormhole Porosity
Pipes are cylindrical or tubular cavities that extend in the weld metal opposite the direction of heat removal. They form from strongly directed gas evolution during rapid solidification.
Physico-chemical mechanism of action
During the welding process, gases are produced, especially carbon dioxide and hydrogen. These gases are held under high pressure in the molten phase. On rapid solidification, these gases cannot be released quickly enough and form cylindrical cavities, known as wormhole porosity. They form due to the directional expansion of the gases against the direction of heat extraction.
Metallurgical relevance & welding risks
Wormhole porosity can lead to various problems. It can impair the mechanical strength and toughness of the weld metal, as it can cause cracks or deformations. Furthermore, it can change the structure of the metals and lead to uneven stress distributions, which in turn can lead to hot cracking.
Workshop practice & action instructions
To minimize wormhole porosity, the following measures should be taken:
• Optimize melting time: Sufficient melting time ensures that the gases release slowly and do not form as pores.
• Gas control: Use gas treatment systems to reduce the carbon dioxide content in the shielding gas mixture.
• Adjust welding parameters: Adjust welding speed and cooling system to ensure uniform solidification and low gas evolution.