What is the minimum diameter of a pressure vessel?

What is the minimum diameter of a pressure vessel?

• A. 4 inches
• B. 6 inches
• C. 8 inches
• D. 10 inches

Answer: (B)

Understanding how vessels are categorized in code rules helps explain why six inches is the turning point. In many welding code frameworks, items designed to hold pressure are treated as pressure vessels, with stricter design, fabrication, and inspection requirements. A common threshold used in exam material is six inches in diameter: vessels at or above this size are classified as pressure vessels, while smaller items are typically treated as piping components or simple tanks and follow different rules. So six inches is the smallest diameter at which the equipment is considered a pressure vessel under the standard references used in this context. The other sizes are either below that cutoff (not treated as pressure vessels in this framework) or not the threshold being tested here.