A thick walled cylinder has an inner radius of 120 mm and an outer radius of 206 mm. To avoid stress corrosion cracking, it is necessary to keep the circumferential stresses at the bore of a thick walled cylinder below -1 MN/m2. This condition is to be achieved by applying an autofrettage pressure. At the working pressure, it has been determined that the equivalent elastic stress is 37. What residual circumferential stress needs to be generated at the bore of the cylinder using the autofrettage process