This problem requires fairly routine substitution into the K equation and the so-called Paris 'law'. The following points may assist you in overcoming any obstacles:
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The choice between thin and thick walled pressure vessel theory is based on the ratio of diameter to wall thickness.
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Remember that internal pressure in a pressurised vessel gives rise to two stress intensity factors, which must be summed.
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Symbolic integration of the Paris law, followed by substitution of values as the last operation, makes easier the of finding arithmetic errors.
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