The number of flexible pipes in operation is increasing due to new field developments and the desire to extend the lifetime of existing fields. There have been many challenges with respect to long term operation of such pipes, in many cases with the need to replace or repair before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. The objective of the present paper is to describe the steps required in order to be able to extend the lifetime of a flexible riser for the case of corrosive annulus environments. A specific riser configuration is considered, and the particular case of outer sheath damage is applied for the purpose of illustration.

The number of flexible pipes in operation is increasing due to new field developments and the desire to extend the lifetime of existing fields. There have been many challenges with respect to long term operation of such pipes, in many cases with the need to replace or repair before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. The present paper summarizes state of the art technology related to operation of flexible pipes and some recent research and development activities that contribute to resolving these issues. In particular, the following topics are addressed: • Fatigue testing of flexible pipes subjected to corrosion damage during operation • Development of improved numerical models and methods for assessment of the residual capacity of flexible pipes • Integrity assessment of flexible pipes also applying quantified risk and reliability assessment • Repair methods for damaged pipe sections In addition, an outline is given of a Handbook (ref. Handbook 2014) which addresses the various topics related to life-cycle design and operation of flexible pipes, see Appendix. Future prioritized research efforts with focus on some of the topical issues given in the list above are finally addressed.

This paper presents results from a case study performed to evaluate the residual capacity of a 6″ flexible pipe when exposed to corrosion damages in the tensile armour. A three-dimensional nonlinear finite element model was developed using the computer code MARC to evaluate the increase in mean and dynamic stresses for a given number of damaged inner tensile armor wires. The study also includes the effect of these damages with respect to the associated stresses in the pressure spiral. Furthermore, the implications of a sequence of wire failures with respect to the accumulated time until cross-section failure in a probabilistic sense are addressed.

There have been many challenges with respect to long term operation of flexible pipes, in many cases with the need to replace or repair them before the end of the initial design life. The number of identified failure mechanisms and observed failure events is also increasing. In the present paper, some typical issues that arise during the process of integrity assessment and qualification for lifetime extension are outlined. More detailed considerations are illustrated in relation to a particular case study. This involves elaboration of the different steps which are required in order to be able to extend the lifetime of a flexible riser for the case of corrosive annulus environments. The particular case of an outer sheath damage is applied for the purpose of illustration.

This paper discusses the structural challenges associated with high axial temperature gradients and the corresponding internal cross section forces. A representative flexible pipe section designed for high operational temperature has been subject to full scale testing with temperature profiles obtained by external heating and cooling. The test is providing detailed insight in onset and magnitude of relative layer movements and layer forces. As part of the full-scale testing, novel methods for temperature gradient testing of unbonded flexible pipes have been developed, along with layer force- and deflection-measurement techniques. The full-scale test set-up has been subject to numerous temperature cycles of various magnitudes, gradients, absolute temperatures, as well as tension cycling to investigate possible couplings to dynamics. Extensive use of finite element analysis has efficiently supported test planning, instrumentation and execution, as well as enabling increased understanding of the structural interaction within the unbonded flexible pipe cross section. When exploiting the problem by finite element analysis, key inputs will be correct material models for the polymeric layers, and as-built dimensions/thicknesses. Finding the balance between reasonable simplification and model complexity is also a challenge, where access to high quality full-scale tests and dissected pipes coming back from operation provides good support for these decisions. Considering the extensive full scale testing, supported by advanced finite element analysis, it is evident that increased attention will be needed to document reliable operation in the most demanding high temperature flexible pipe applications.