Recovery length of high strength tapes in damaged flexible pipes

• A simple method for reestablishing the initial restraint capacity in damaged flexible pipes is proposed.
• The recovery length of filament used in repair method is obtained and its solution is expressed in non-dimensional form.
• The mechanical behavior of both perfect and damaged High Strength Tapes in flexible pipes is presented.
• Analytical formulations that depict the restraint ability of undamaged High Strength Tapes are derived.
• The influence of some important parameters on the recovery length is discussed.

The application of filaments wound around damaged high strength tapes (HSTs) in flexible pipes may be one of the simplest methods to reestablish the initial restraint capacity for the armor wires. This paper aims at evaluating the effectiveness of such method observing the recovery length of filaments and investigating the mechanical behavior of both perfect and damaged HSTs. Analytical formulations that depict the restraint ability of undamaged HSTs are derived from a combination of Clebsch–Kirchhoff equilibrium equations and a modified non-linear friction law in terms of normal stress. As a base case, the restraint ability induced by the interaction between original damaged HSTs and filaments is obtained as well as the required recovery length. The solution is presented in non-dimensional form and it is shown that the repair method is feasible. Besides, some important parameters affecting the recovery length are investigated. It is found that the application of tension force at both ends of filament is the most effective way to reduce the recovery length. It is also shown that external pressure has insignificant effect if tension forces at ends are large. In addition, a case study shows that the recovery length grows almost linearly with the increasing radius of tape.