cranfield university mahadi abd murad an integrated structural ...

Simola et al. (2009) present several project studies with the purpose of
investigating reasonable and practical requirements that should be set for assumptions
about the accuracy of how inspection reliability is quantified in terms of POD. Their
pilot studies resulted in a set of recommendations related to the quantification of
inspection qualification. In addition, if defect growth can be modelled further, it is
possible to link inspection qualification results, risk reduction and inspection intervals.
According to Reboud et al. (2010), POD curves relate the detectability of a flaw
to its size. For a specific inspection method, the POD expresses the probability that it is
a flaw of a certain size that will be detected, assuming this flaw is actually present in the
inspected component. Traditional POD curves are estimated from experimental data, the
large amount of data required makes the determination of a reliable POD curve very
expensive and time-consuming if there is a lack of support and contribution by the
relevant organisations as addressed by Brennan et al. (2009) earlier. One of the
solutions is using a simulation approach. Reboud et al. (2010) have used CIVA, a
software for statistical tools, enabling POD computations to bring a cheaper and faster
complement to POD studies. These simulation-based POD calculations have been
recently introduced in the NDE community as reported by Jenson et al. (2009).
2.4 Maintenance Strategy
Maintenance strategy is one of the important sub-components of the life
extension programme which is under the pipeline integrity system as referred to in
Figure 1.2 in Chapter 1. There is the possibility of ending up with a catastrophic disaster
caused by ageing and/or other factors if this strategy is not properly carried out by
operators.
An example of damage or disaster due to ageing has been studied by Kotrechko
et al. (2002). They conclude that from their low temperature testing results, the long-
term operation does not affect the microscopic cleavage resistance (minimum brittle-
fracture stress) of steel and has no influence on the strain-hardening exponent. But the
26