Which Methods should an Operator Use and How Should they be Optimised?

A method for determining which method to use, and on which pipeline, is a 'Prioritisation Scheme'. These type of schemes are increasingly being used to guide operators on the optimum use of maintenance and inspection methods. For example, if a pipeline's major 3 cause of damage is third party interference, increased surveillance or the introduction of a One-Call System may be appropriate preventative maintenance methods. However, if a pipeline is failing due to internal corrosion, then an internal inspection using an intelligent pig would be appropriate.

A Prioritisation Scheme considers the probability and consequences of failure within a group of pipelines (or sections of a single pipeline) by systematically assessing the pipelines' design, operation and failure history. Points are allocated for design, operation and failure history. High points indicate high risks. For example, the probability of failure due to external corrosion is evaluated by considering the quality of the pipe coating, CP system, etc., and the consequences of failure are considered by estimating the density of surrounding population, security of supply, etc.
The great advantage of this scheme is that it can:
i. rank all the pipelines within a group (or sections of a pipeline) in terms of probability of failure, and consequences of failure,
ii. determine which pipeline (or section of a pipeline) is most in need of some type of maintenance measure,
iii. determine which maintenance measure to use.
There is now no need for a pipeline operator to 'guess' which part of his system needs maintenance, and he now does not to have wait for a section of his system to show signs of deterioration. The Priority Scheme is a proactive method of setting maintenance and inspection schedules. Figure 2a shows a readout of one particular scheme. This scheme has been used to rank seven pipelines. Clearly pipeline number seven is the highest risk pipeline. Figure 2b shows the second analysis the Scheme conducts on pipeline number seven.

Figure 2b shows that this pipeline is most at risk from internal corrosion, therefore an internal inspection is necessary. Figure 3a shows the results of a re-run of the Prioritisation Scheme to quantify the effect of the internal inspection on pipeline number seven. Now, pipeline two is the highest risk, and Figure 3b shows third party interference to be the major risk to pipeline two. The operator can now consider increasing surveillance to reduce this risk.