Page 281 - Pipelines and Risers

254 Chapter 14

Table 14.3 Operating Years Inspection Until the Target Failure Probability.
I I Effect of Inhibitors I
I PRed. I 0% I SO% I 60% I 70% I 80% I
0% 1 3 4 6 12

8 13 1s 19 23
30% 9 15 17 21 29
14.6.2 Rehabilitation

A possible major repair alternative is replacement of a fraction of, or the whole pipeline. The
major repair/modification can greatly reduce the estimated failure probability. However, as
the observed damage can be effectively controlled by the minor repair/modifications, the
major modification is not recommended in the requalification process of this pipeline.

14.7 Conclusions

The existing criteria for corroded pipelines (ASME B31G) were reviewed. The new criteria
were developed based on the analmcal, experimental, and numerical studies. Safety factors
for the new criteria were calibrated using the reliability method. This calibration deliver the
same safety level implied in the existing B31G criteria. The new criteria were applied in the
requalification of the existing corroded pipelines.

14.8 References

1. ASME (1996), “B31G - Manual for Assessing Remaining Strength of Corroded Pipes”,
American Society of Mechanical Engineers.
2. Bai, Y. and Mgrk, K. J. (1994) “Probablistic Assessment of Dented and Corroded
Pipeline” International Conference on Offshore and Polar Engineering, Osaka, Japan.
3. Bai, Y., Xu, T. and Bea, R., (1997) “Reliability-based Design and Requalification Criteria
for Longitudinally Corroded Pipes”, ISOPE97.
4. BSI (1991) “PD6493 - Guidance on Methods for Assessing the Acceptability of Flaws in
Fusion Welded Structures”.
5. Folias, E. S., (1965) “An Axial Crack in a Pressurised Cylindrical Shell”, Int. J. of
Fracture Mechanics, Vol. 1 (l), pp.64-113.
6. Galambos, T.V. (1988) “Guide to Stability Design Criteria for Metal Structures”, John
Wiley 8z Sons, Inc. pp. 502-508.
7. Hopkins, P. and Jones, D. G., (1992) “A Study of the Behaviour of Long and Complex-
shaped Corrosion in Transmission Pipelines”, Proceedings of OMAE’92.
8. Jones, D. G., Turner T. and Ritchie, D. (1992) “Failure Behaviour of Internally Corroded
Linepipe”, OMAE’92.