The formula t = PR/SE is used to calculate which of the following?

• A. Hydrostatic testing
• B. Shell thickness for internal pressure
• C. External pressure design
• D. Safety valve sizing

Answer: (B)

This formula is used to determine the minimum shell thickness needed for a vessel under internal pressure, using a thin-walled assumption. When internal pressure acts on a cylinder, the hoop stress in the wall is roughly σ ≈ P·R / t. To keep stress within what the material and its joints can safely carry, you require σ ≤ S·E, where S is the material’s allowable stress at the design temperature and E is the joint efficiency (accounts for welds or connections). Solving for thickness gives t = P·R / (S·E). So the formula directly provides the required wall thickness to resist internal pressure.

This isn’t the method used for hydrostatic testing thickness, external pressure buckling design, or safety valve sizing, which rely on different relationships and factors.