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Reliability-Based Strength Design of Pipelines 227

deepwater and harsh environments, project specific design criteria can be established by use
of finite elements and reliability methods.

It is difficult (if at all possible) to define code criteria which can cover all combinations of
design scenarios (e.g. installation, hydro tests, operation), pipe materials (e.g. corrosion
defects), loads (high hoop stress and low hoops stress cases) and new phenomenon which
appear in challenging projects. Therefore, subject to achievable cost-saving and technical
qualification, design engineers should develop project-specific design criteria based on the
direct use of the reliability-based calibration under the principles of the NORSOK standard Y-
002 (1997).

13.6 Conclusions
The chapter presents reliability-based limit-state design and re-qualifications of pipelines.
Following a summarized discussions of reliability and uncertainty measures, target reliability
levels and calibration of safety factors, the following two limit-state design applications are
given .

(1) Design factors for hoop stress criterion: it is shown how the usage factor has been derived
using reliability-based calibration.

(2) Bucklinglcollapse of Corroded Pipes: the causes of the conservatism in the existing codes
were identified and the reliability-based determination of partial safety factors was discussed.
Further study is required to refine uncertainty measures and to develop methodology for the
determination of partial safety factors for finite element models and laboratory tests.

13.7 References

1. Bai, Y. and Damsleth, P.A., (1998) “Design Through Analysis Applying Limit-state
Concepts and Reliability Methods”, Roc. of ISOPE98. A plenary presentation at
ISOPE’98.
2. Bai, Y. and Hauch, S., (1998) “Analytical Collapse Capacity of Corroded Pipes”, Proc. of
ISOPE’98.
3. Bai, Y. and Song, R., (1997) “Fracture Assessment of Dented Pipes with Cracks and
Reliability-based Calibration of Safety Factors”, International Journal of Pressure Vessels
and Piping, Vol. 24, pp. 221-229.
4. Bai, Y., Xu, T. and Bea, R., (1997) “Reliability-based Design & Re-qualification criteria
for Longitudinally Corroded Pipelines”, Proc. of ISOPE ‘97.
5. DNV (1996) “Rules for Submarine Pipelines”, Det Norske Veritas.
6. Guedes Soares, C., (1997) “Quantification of Model Uncertainty in Structural Reliability”,
in Probabilistic Methods for Structural Design, edited by C. Guedes Soares. Kluwer
Academic Publishers.
7. Hauch, S. and Bai, Y., (1998) “Use of Finite Element Methods for Local Buckling Design
of Pipeline”, Proc. of OMAE ‘98.