What type of welding does the 'root pass' refer to?

The term "root pass" specifically refers to the initial layer of weld metal that is deposited to join two base metals at their root, which is the point of contact between them. This stage is crucial because it establishes the foundation for subsequent layers of weld material and helps ensure that the weld joint will be strong and well-penetrated.

The root pass is particularly important in multi-pass welding processes, as it affects the integrity and quality of the weld. Proper execution of the root pass is essential for developing a sound weld joint, as it ensures that there is adequate fusion between the base metals at their most critical interface.

Overall, the root pass is not just a single-layer weld or a final pass, but rather it denotes the essential first step in the welding sequence that sets the tone for the entire process. This importance can also be highlighted when considering that it provides the foundation for the following passes, which build upon it to achieve the desired weld profile and strength.