How many passes are required for welds on Groups IV, IVA, V, or VI shell-to-bottom welds?

• A. One pass
• B. Two passes
• C. Three passes
• D. Four passes

Answer: (B)

For shell-to-bottom welds associated with Groups IV, IVA, V, or VI as defined in the API 650 standard, a two-pass weld is required. The rationale behind requiring two passes is primarily based on the structural and integrity requirements specific to these groups, which may involve thicker materials or higher stress areas due to their service conditions.

The first pass is typically a root pass that establishes initial penetration and joint integrity, while the second pass serves to provide additional reinforcement and ensure a sound weld bead that meets the specified mechanical properties and fatigue considerations. This two-pass system helps mitigate issues like cracks or lack of fusion that may compromise the weld's effectiveness in supporting the weight and operational stresses of the tank structure.

Understanding the welding requirements specific to these material groups is crucial for ensuring compliance with safety and performance standards in welded tank construction.