What is the purpose of the root pass in a multi-pass groove weld?

What is the purpose of the root pass in a multi-pass groove weld?

• A. To remove slag after welding.
• B. To clean the weld surface with solvent.
• C. To establish the weld root and penetration; subsequent passes fill and cap.
• D. To attach fixtures for the next weld.

Answer: (C)

The main idea is that the root pass creates the foundation of the weld by fusing the base metal at the joint root and achieving proper penetration. This initial pass establishes a solid root that securely joins the pieces and provides a reliable base for the rest of the weld. Once the root is established, the subsequent passes are used to fill the groove and cap the weld, building up thickness and shaping the final surface. If the root pass doesn’t achieve good penetration, you risk lack of fusion at the root and a weak weld, and the filler and cap passes won’t compensate for that base. Slag removal happens after each pass, not as the purpose of the root pass. Cleaning with solvent is not part of forming the root, and attaching fixtures is a separate, mechanical step outside the welding process.

The main idea is that the root pass creates the foundation of the weld by fusing the base metal at the joint root and achieving proper penetration. This initial pass establishes a solid root that securely joins the pieces and provides a reliable base for the rest of the weld. Once the root is established, the subsequent passes are used to fill the groove and cap the weld, building up thickness and shaping the final surface. If the root pass doesn’t achieve good penetration, you risk lack of fusion at the root and a weak weld, and the filler and cap passes won’t compensate for that base.

Slag removal happens after each pass, not as the purpose of the root pass. Cleaning with solvent is not part of forming the root, and attaching fixtures is a separate, mechanical step outside the welding process.