A steel pipe of 12-in outer diamer is fabricated from 1/4-in-thick plate by welding along a helix that forms an angle of 25 degrees with a plane perpendicular to the axis of the pipe. Knowing that the maximum allowable normal and shearing stresses in the directions respectively normal and tangential to the weld are s = 12 ksi and t = 7.2 ksi, determine the magnitude P of the largest axial force that can be applied to the pipe.