The best approach is to put in context the integrity of the line viz a viz the economics of managing continued usage. You can draw up a monitoring program for intelligent pigging to know the state of you pipelines.
With the informatin gathered, you should be able to determine if:
1 The line is suceptible to failures and at what points
2 The possibility of derating the line and consequence on production
3 The cost of repairs
4 The reliability of repairs
5 The overall probability of failure
6 The economic and environmental impact of a failure
7 Policies and legislation
The age of a pipeline is a principal determinant in the retiremetn of a pipeline. however with goood asset intergrity management practice a line can be in active service well over its design life.
One must not also forget the development philosophy in the initial design of the lines in question as this can also affect the decision of which line ,and when it, should be retired.
Greg Akhibi
SPDC Nigeria
