Life extension and upgrading of structures to meet increased structural integrity requirements

During the design life of structures there may be changes in safety requirements which lead to the need to be able to demonstrate higher structural integrity for the life extension than was required at the design stage. Essentially this can be regarded as a requirement to demonstrate a given target reliability level for extended life taking account of any degradation of the structure so far. This demonstration of enhanced reliability may be achieved by improving the quality of information available. perhaps by closer control of operating conditions, by more sophisticated structural/stress analysis, by improved information about material properties from testing of samples removed from the structure or by results from in service inspections to provide improved information.