Which method poses a higher risk of tungsten inclusions?

The scratch start method poses a higher risk of tungsten inclusions primarily due to the way it initiates the arc. In this method, the tungsten electrode is physically scratched against the workpiece to create a short circuit. This contact can lead to small particles or debris being transferred from the electrode to the weld puddle. Additionally, if the tungsten electrode itself breaks during this process, it can further increase the likelihood of tungsten contamination in the weld.

In contrast, methods such as lift start and high frequency start minimize the contact between the electrode and the workpiece. Lift starting involves bringing the tungsten electrode close to the surface, lifting it slightly to initiate the arc without touching the material, thereby reducing the risk of inclusion. High frequency starting uses an oscillating electric field to create the arc without direct contact, making it even less likely for the electrode to introduce contaminants.

Post flow start is not a method of starting but rather refers to the gas flow after the welding arc has been extinguished, adding no risk of tungsten inclusions at the initiation phase.

Overall, the scratch start method increases the risk of tungsten inclusions due to physical contact and the potential transfer of material into the weld.