R = radius to point in tube or cylinder wall (mm, in) (r i < r < r o) Σ c = stress in circumferential direction (MPa, psi) The stress in circumferential direction - hoop stress - at a point in the tube or cylinder wall can be expressed as: R o = external radius of tube or cylinder (mm, in) Stress in Circumferential Direction - Hoop Stress R i = internal radius of tube or cylinder (mm, in) P o = external pressure in the tube or cylinder (MPa, psi) P i = internal pressure in the tube or cylinder (MPa, psi) Σ a = stress in axial direction (MPa, psi) Σ a = (p i r i 2 - p o r o 2 )/(r o 2 - r i 2) (1) The stress in axial direction at a point in the tube or cylinder wall can be expressed as: When a thick-walled tube or cylinder is subjected to internal and external pressure a hoop and longitudinal stress are produced in the wall.
