Answer Happy

Pressure vessels are conventionally designed according to either criteria called "yield before break” or “leak before break". Smaller pressure vessels typically being designed according to the former criteria, larger pressure vessels typically being designed according to the latter "leak before break” criteria a) In terms of anticipated material behaviour, review the fundamental principles of pressure vessel design criteria of "yield before break” (3 marks) b) Figure Q2 shows a schematic cross section through a "thin walled" spherical pressure vessel of internal radius, R and wall thickness, t. An internal crack (eg. weld centreline crack) of length 2a can be assumed to be present in the vessel wall as shown in figure Q2. Derive an expression based on "yield before break” criteria in terms of maximising the critical crack size when the hoop stress (o) in the vessel walls (induced by internal pressure, P) equates to the yield stress. The derived expression for critical crack size containing a material performance index (in the form to be maximised) that can be used for prudent material selection for safety according to "yield before break” principles. (5 marks)