Consider a stress element located on the welded tank seam.
The longitudinal and hoop stresses act in the directions shown.
For this problem, the normal stress acting perpendicular to the weld seam and the shear stress acting parallel to the seam are to be computed. Therefore, the direction of the normal to the weld seam plane must be determined.
The normal to the weld seam plane is at an angle of θ = –65°.
Use θ = –65° in the stress transformation equations to determine the weld stresses.