Once the critical crack size calculated in problem three is exceeded, the crack will propagate through the thickness of the protective acmite coating and terminate at the inner steel vessel wall. This then allows the caustic sodium hydroxide to reach the steel wall and the corrosion process begins. Take the mode I fracture toughness for A$5$xx series steels to be $85$MPa$\sqrt[\phantom{2}]{m}$ and $Y=1.$ Using your axial and tangential stresses calculated in problem one, determine the maximum length of a surface flaw that is possible without fracture of the steel vessel. Comment on your result with respect to plausible methods of identifying these cracks via inspection. $($Refer to Table $8\mathrm{.}2$ on page $263$ of your text$).$