A Theoretical Approach to Predict the Fatigue Life of Flexible Pipes

Table 1

Possible contact pressures and stress in the high-strength (HS) tape for a typical unbonded flexible pipe considering different annulus conditions and axisymmetric loading.

Shape	Interface^†					Stress (HS tape)	Annulus
	1	2	3	4	5
1	Contact	Contact	Contact	Contact	Contact	Unloaded
2	No contact	Contact	Contact	Contact	Contact	Tensioned
3	No contact	Contact	Contact	Contact	Contact	Unloaded
4	No contact	Contact	Contact	No contact	Contact	Tensioned	Dry
5	No contact	Contact	Contact	Contact	No contact	Unloaded
6	No contact	Contact	No contact	No contact	Contact	Tensioned
7	Contact	Contact	Contact	Contact	No contact	Unloaded
8	Contact	Contact	Contact	Contact	Contact	Unloaded
9	No contact	Contact	Contact	Contact	Contact	Tensioned
10	No contact	Contact	Contact	Contact	Contact	Unloaded
11	No contact	Contact	Contact	No contact	Contact	Tensioned
12	No contact	Contact	Contact	Contact	No contact	Unloaded	Flooded
13	Contact	Contact	Contact	Contact	No contact	Unloaded
14	Contact	No contact	Contact	No contact	Contact	Tensioned
15	Contact	No contact	Contact	Contact	No contact	Unloaded
16	Pure external pressure

^†Interface 1: inner carcass and internal plastic sheath; interface 2: internal plastic sheath and pressure armor; interface 3: pressure armor and antiwear tape (or tensile armor); interface 4: pressure armor (or antiwear tape) and internal tensile armor; interface 5: external tensile armor and polymeric layer upon it. In all other interfaces, contact between layers was observed.