If joint efficiency decreases, what happens to the required shell thickness?

• A. Increases
• B. Remains the Same
• C. Decreases
• D. Becomes Zero

Answer: (A)

The key idea is that the shell thickness is based on how much stress the shell can safely carry, which is determined by the material’s allowable stress times the joint efficiency. Joint efficiency represents how much of the weld or joint can actually carry the load. In design calculations, the allowable stress used in sizing is effectively the material allowable stress times this joint efficiency (S × E). If the joint efficiency decreases, the available strength drops. To keep the same internal pressure and geometry within that reduced strength, the shell must be thicker. In simple terms, the required thickness is inversely related to the joint efficiency (t ∝ 1/E). So when joint efficiency goes down, the required shell thickness must go up. This is why the correct answer is that the thickness increases.