If joint efficiency decreases, which design parameter is increased?

If joint efficiency decreases, which design parameter is increased?

• A. Wall thickness
• B. Wall diameter
• C. Material cost
• D. Operating pressure

Answer: (A)

When joint efficiency drops, the joints contribute less to the vessel’s strength, so the allowable stress that the wall can safely carry is reduced. For a thin-walled pressure vessel under internal pressure, the hoop stress is balanced against the allowable stress, roughly described by P·D/(2t) ≤ S·η_j. If η_j decreases, the right side becomes smaller, and the thickness t must increase to keep the inequality true. So the design parameter you raise to compensate is the wall thickness. Increasing diameter would not fix the reduced joint strength and, in fact, tends to raise the required thickness. The material cost and operating pressure aren’t used to counteract a decrease in joint efficiency in this context.

When joint efficiency drops, the joints contribute less to the vessel’s strength, so the allowable stress that the wall can safely carry is reduced. For a thin-walled pressure vessel under internal pressure, the hoop stress is balanced against the allowable stress, roughly described by P·D/(2t) ≤ S·η_j. If η_j decreases, the right side becomes smaller, and the thickness t must increase to keep the inequality true. So the design parameter you raise to compensate is the wall thickness. Increasing diameter would not fix the reduced joint strength and, in fact, tends to raise the required thickness. The material cost and operating pressure aren’t used to counteract a decrease in joint efficiency in this context.