Calculate the maximum crack length permissible in a steel pressure vessel at the maximum safe operating pressure of 20.4 MPa. The pressure vessel is 0.50 m in diameter and has a 5 mm wall thickness. Assume that failure occurs when the hoop stress in the pressure vessel reaches the yield stress (510 MPa). The hoop stress (σ) in the pressure vessel (diameter: 2R) is related to pressure (p) by p = (2σ t/R), where t is wall thickness. Given: Mode I fracture toughness of steel is 50.4 MPa√m and the geometric parameter Y is 1.5