Page 518 - Pipelines and Risers

LCC .Modeling as a Decision Making Tool in Piperine Design 485

NOK 29.wO.wO
NOK 28.WO.WO
NOK 27 000 000
NOK 26 000 000 LOW Ouallhl
8 NOK 25 000 000 mHmamw
NOK 24.000 000
NOK 23 000 000
NOK 22 000 000
, 2 3 4
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Figure 25.3 Comparison of LCC for alternative ambinatlons.

25.6 On-Bottom Stability Example

25.6.1 Introduction
This example will outline the use of LCC modeling when deciding the method by which to
stabilize a pipeline. This problem will only be discussed in general terms from which it would
be possible to complete a more detailed assessment.
25.6.2 Step 1- Definition of System

The system to be considered is a pipeline.
25.6.3 Step 2- Quality Aspects Considered
The quality aspect to be considered is on-bottom stability. From this it is possible to identify
different mechanisms by which the pipeline may be stabilized. These include:

ConCree Coating
RockDumping
Dynamic Stability

25.6.4 Step 3- Failure Modes
The failure modes, which exist for on-bottom stability design criteria, are:

0 Sliding Lateral Stability
0 Uplift Vertical Stability

Given the high degree of correlation between the uplift and sliding modes of failure, the
probability of stability failure is equal to the maximum of either the probability of sliding
failure or the probability of uplift failure.