Annulus Testing for Condition Assessment and Monitoring of Flexible Pipes

Abstract

The Norwegian operator Norsk Hydro has more than 80 flexible dynamic risers and service lines in operation at different platforms. Riser integrity monitoring programs have been established for the flexible risers in order to ensure safe and reliable operation. SeaFlex has performed annulus testing on a large number of these risers as a part of the programs. The free annulus volume of a flexible pipe is defined as the volume between the extruded internal pressure barrier layer and the extruded external sheath subtracted the volume occupied by pressure- and tension armor, tape and eventual other layers. Two methods are presently used by the industry for annulus free volume testing of flexible pipes, namely nitrogen pressure testing and vacuum testing. Both methods identify trends of volume reduction with time and to detect annulus flooding. Annulus testing has proven to be an efficient and reliable tool for detecting annulus flooding, blocked vent ports and outer sheet damages. This paper address the challenges related to annulus testing of flexible pipes, advantages, experiences and how such tests and the results are used for condition assessment and monitoring of the risers.

RFID wireless system for detection of water in the annulus of a flexible pipe

“…Determination of whether the annulus is flooded or not has been attempted in different manners, i.e. through the positive pressure or the vacuum tests, visual or ultrasonic inspection, or by fiber optics sensing [13][14][15]. The positive pressure and the vacuum tests require vents that connect to the annular region; often these tests do not produce accurate results or cannot be performed due to operational issues (i.e.…”

“…The positive pressure and the vacuum tests require vents that connect to the annular region; often these tests do not produce accurate results or cannot be performed due to operational issues (i.e. vent blockage) [13,14]. Visual inspection can be used to encounter breaks in the outer sheath, but small abrasions or cuts can easily be missed along the vast extension of a riser.…”