Analysis of End Fitting Barrier Seal Performance in High Pressure Unbonded Flexible Pipes

Abstract

End fitting is an essential component of flexible pipes enabling their connection between moving structures and pipes to create a complete pipe infrastructure. Designing the end fitting requires careful consideration of many factors including creating an effective barrier seal, termination of all the polymer and metal layers and anchoring armor layers so that the external loads of the pipe are transferred to the connecting structure without disturbing the seal. The most difficult challenge in designing end fittings for ultra-high pressure pipes is creating the necessary barrier sealing performance. In general, the seal needs to perform to approximately twice the design pressure of the pipe so that it can sustain the burst condition of the pipe. This requires the sealing components to be subjected to extreme loading where most of the sealing components are subjected to severe plastic deformation. Understanding seal deformations and quantifying and demonstrating sealing performance are important in the development of a reliable seal. This paper describes a method of evaluating the sealing performance of end fitting seals. Design requirements of end fitting seals are also described. The barrier seals in end fittings are normally created by swaging a metal seal ring in between the polymer barrier and the body of the fitting. This creates two leak paths, one between the metal ring and the barrier and the other at the metal-to-metal contact interface between the seal ring and the body. Achieving sufficient compression on the polymer barrier and creating sufficient contact pressure over a reasonable distance at the metal-to-metal interface are the key requirements in developing a reliable high pressure barrier seal. During this study, finite element models have been used to evaluate the contact pressure at seal contacts. These results, with a specifically developed leak criteria, have been used to evaluate the sealing performance. A brief description of the models and some specific results are presented. The FE model predictions are compared with the actual contact pressure measurements of a sealing setup.

Sealing Performance Analysis of an End Fitting for Marine Unbonded Flexible Pipes Based on Hydraulic-Thermal Finite Element Modeling

“…The maximum contact pressure along path 2 is 195.6 MPa, which is much larger than the design pressure and test pressure of the end fitting. This indicates that there will be no seal leakage along this path, which is consistent with the results of previous works [22,23]. Hence, we focus on path 1 in the following analysis.…”

“…The sealing assembly in an end fitting is usually formed by swaging a metallic sealing ring into the area between the polymeric layer and the end fitting body. During assembly, the contact surface between the sealing ring and the end fitting body and between the sealing ring and the polymeric sheath creates two leakage paths [14,22]. Path 2 is the metal-to-metal microscopic gap between the end fitting body and the sealing ring, where a higher contact pressure ensures better sealing capacity.…”

“…However, calculating the critical failure pressure is complicated, and the influence of the material and the medium should be considered. In a previous study [22], the nominal critical failure pressure was expressed as…”

“…For an end fitting in a high-pressure pipe, it is challenging to create the necessary sealing performance. Fernando et al [22] developed an FE model of a flexible pipe end fitting and presented a method of evaluating the sealing performance of the sealing assembly and the design requirements for the sealing assembly of the end fitting. In their work, FE analysis was conducted using specially established leak criteria.…”

Design, Manufacturing and Testing of Pipe Fittings

“…Impermeability is achieved by preventing leakage from the pipe fitting. Fernando and Karabelas [1] state that the effect of sealing is found by observing the amount of liquid leaking.…”