Abstract From the increasing demand of flexibles product for gas production for ultra-deepwater fields, a new design complication is emerging: a water ingress from the external environmental towards the bore of the flexibles. This phenomenon, called Front Sealing Back Pressure (FSBP), challenges end-fittings existing front sealing system on the pressure sheath, noticeably during shutdowns. Those phases can expose the products to high differential pressure and low temperature, creating a potential for liquid water penetration in the bore though front sealing system, with a consequent risk of hydrate formation, not acceptable for some applications. The FSBP phenomenon has been reproduced through tests and its occurrence is mainly impacted by the material of the pressure sheath, temperature and differential pressure that the product is exposed to during its service life. In order to prevent FSBP, an enhanced sealing solution has been developed by introducing an additional barrier to the existing front sealing system of the end-fitting. The solution, called “backseal” is a recently introduced technology, that allows enhancing the sealing performance of front sealing system against external pressure, without compromising other functions of the end-fittings. As described in this paper, the “backseal” solution has been firstly qualified based on multiple end-fitting mounting trials. Then, during the qualification, the “backseal” has been exposed to different combination of loads (internal pressure / external pressure/temperature), representative of product life cycle, from end-fitting mounting to operation until the end of service life. During the qualification of the “backseal”, a finite element model has been developed and used to evaluate the sealing performance of the seal in different scenarios. The finite element model predictions demonstrated to be in line with the results from qualification tests. At last, the “backseal” solution has been certified by a third-party for compliancy versus design requirements of API SPEC 17J, NORSOK M-710 and ISO 23936-2, and covered the qualification testing campaign, engineering, procurement, and mounting for a wide design envelope, that includes different pressure sheath materials and water depth beyond 3000 m.
Frigeri et al. (Sun,) studied this question.