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Figure 2.9: Pipeline failure probability with time. Effect of repairs on safe working<br />

life (time to next inspection) <strong>an</strong>d re-inspection intervals (Hallen et al., 2003)<br />

According to Waym<strong>an</strong> (2008), when the system containing large numbers of<br />

interdependent variables with associated uncertainties c<strong>an</strong>not be dealt with effectively in<br />

a wholly deterministic m<strong>an</strong>ner (Brenn<strong>an</strong> et al., 2006) or direct inspection such as using<br />

a pig mounted system is not possible (Waym<strong>an</strong>, 2008), then probabilistic me<strong>an</strong>s or<br />

statistical models to predict the condition of length of pipeline based on selective<br />

external local inspection are required.<br />

Therefore, the reliability of information literally depends on the pipeline damage<br />

database created, based on the result of pipeline inspection <strong>an</strong>d monitoring. According<br />

to Greenwood (2002), the purpose of having a damage database or information is to:<br />

Estimate leak <strong>an</strong>d pipeline rupture frequencies, based directly on historical<br />

failure rates data<br />

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