The polymer barrier is the most important component in unbonded flexible pipe, providing the leak-tight boundary for transporting hydrocarbon medium. Premature failure of the barrier during service can be costly and may lead to disastrous environmental consequences. Design of the barrier for 25 years’ service integrity is therefore a major requirement in the flexible pipe design process. However, the API design code does not give a specific procedure for the design of the barrier and is mainly concerned with the design of other layers in the pipe which are intended to provide integrity to the polymer barrier.
The selection of barrier material depends on many factors including the service temperature/pressure range and pipe bending requirements. Polyvinylidene fluoride (PVDF) is used as a barrier material in cases where high pressure and relatively high temperature applications are involved. However, a hard polymer such as PVDF can be susceptible to crazing and cracking under specific conditions and therefore the use of PVDF in flexible pipe barriers requires critical consideration of the above issues.
This paper discusses the general design requirements of a single layer barrier, and different barriers in relation to static and dynamic applications. The details of a qualification test program performed to establish service integrity of single layer Solef 60512 PVDF barriers is discussed. The unique testing facilities developed to test the integrity of the barrier are presented.