A Theoretical Approach to Predict the Fatigue Life of Flexible Pipes

Table 2

Load characteristics for each possible deformed shape of a typical unbonded flexible pipe considering different annulus conditions and axisymmetric loading.

Shape	Load characteristics^†	Annulus
1	High tension (no axial compression), low internal pressure, high external pressure, moderate torsion
2	Low tension or axial compression, high internal pressure, low external pressure, low torsion
3	High tension, high internal pressure, moderate external pressures (internal pressure higher than external pressure), low torsion
4	High axial compression (no tension), high internal pressure, low external pressure, low torsion	Dry
5	High tension and internal pressure, no external pressure, moderate torsion
6	High axial compression, low internal and external pressures, low torsion
7	High tension and low internal and external pressures, low torsion
8	Analogous to shape 1
9	Analogous to shape 2
10	Analogous to shape 3
11	Analogous to shape 4
12	Analogous to shape 5	Flooded
13	Analogous to shape 7
14	High axial compression, no internal pressure, high external pressure, low torsion
15	High tension, no internal pressure, high external pressure, low torsion
16	Pure external pressure

^†The fundamental aspect is to maintain the proportionality between the loads. Therefore, a high load value could be its limit for the studied flexible pipe; a low value may be, for instance, 1% of the limit value, and a moderate value could be 50% of the limit value.