If joint efficiency equals 1.0, how does the required thickness compare to a lower efficiency?

• A. Increases
• B. Becomes zero
• C. Decreases
• D. Remains the same

Answer: (C)

Joint efficiency tells you how much of the weld joint’s strength can be relied on in the design. In the thickness calculation, the allowable strength is effectively the base material strength times the joint efficiency. A higher efficiency means the welds contribute more to resisting the internal pressure, so you can use a thinner wall and still meet the same strength requirements. When the efficiency is 1.0, the welds are treated as strong as the base metal, so there’s no penalty for weld weaknesses. Compared with lower efficiencies, you don’t need extra thickness; therefore the required thickness decreases.