What is the practical effect of reducing joint efficiency on required thickness?

What is the practical effect of reducing joint efficiency on required thickness?

• A. The required thickness increases
• B. The required thickness decreases
• C. The required thickness remains unchanged
• D. The required thickness becomes zero

Answer: (A)

Reducing joint efficiency lowers the effective strength carried by the welded joints. In design, the welds are allowed to carry only a fraction η of the full material strength. For a cylinder under internal pressure, the hoop stress that must be withstood is roughly P D / (2 t). The allowable stress is the material strength S multiplied by the joint efficiency η, so the design condition is P D / (2 t) ≤ S η. Solving for thickness gives t ≥ P D / (2 S η). When η decreases, the right-hand side grows, meaning you must increase the wall thickness to maintain the same safety margin. So the practical effect is that the required thickness increases.

Reducing joint efficiency lowers the effective strength carried by the welded joints. In design, the welds are allowed to carry only a fraction η of the full material strength. For a cylinder under internal pressure, the hoop stress that must be withstood is roughly P D / (2 t). The allowable stress is the material strength S multiplied by the joint efficiency η, so the design condition is P D / (2 t) ≤ S η. Solving for thickness gives t ≥ P D / (2 S η). When η decreases, the right-hand side grows, meaning you must increase the wall thickness to maintain the same safety margin. So the practical effect is that the required thickness increases.