Page 280 - Pipelines and Risers

Remaining Strength of Corroded Pipes 253

Figure 14.12 Expected Corrosion Depth Over Time for Different Inhibitors.

c I I I I I I I I I
5

Figure 14.13 Annual Failure Probability for Different Inhibitors.

Evaluation of Alternatives
The selection of the minor repair/modification alternatives (de-rating or inhibitors) satisfies
the constraints. Table 14.3 summarizes the combination effects. It summarizes the operating
time after 10 years service until the target probability is reached.

If the next inspection is not scheduled prior to 15 years of service, the combinations of de-
rating and inhibitors in the shaded area of Table 14.3 are the realistic decision alternatives.
The darker shaded area indicates the most attractive combination of use of inhibitor with
specified effect and degree of pressure reduction. If the pipeline inspection is rescheduled, the
alternatives of upper left comer in Table 14.3 are recommended. However, in the evaluation
of the alternatives incorporating a reduction of the time period until next inspection, the
likelihood of possible major repaidmitigate measures at an earlier period should be addressed
in the decision process.