The circumferential stress, , (also called hoop stress) in a pressurized cylindrical vessel is calculated by the equation =Prt , where P is the internal pressure, r is radius of the vessel, and t its thickness. Assume a vessel of 38 in. diameter, 0.25 in. thickness, and having an internal pressure of 5000 psi. Use Table 7.1 for properties. (Use Y = 1.0 and assume center crack geometry.) The image is a cylinder with circumferential stress, , internal pressure, P, and radius r has a crack in the center.

What would be the critical crack length if the vessel were made of Al 7178-T651. The critical crack length would be ______ in. (Round the final answer to four decimal places.)