ASSESSMENT OF LOADING ON THE CARCASS AND PRESSURE ARMOUR DUE TO ENVIRONMENT SWELLING OF POLYMER

摘要

Flexible pipes consist of multi-layer structures comprising polymer extrusions, tapes and insulation that are trapped between layers of helically-wrapped steel wires. Under certain pressure and temperature service conditions, and when the polymers are in contact with certain chemicals (such as supercritical CO2), these polymer layers may experience significant volumetric changes caused by permeation, solubility and absorption of chemicals into the polymer structure. The swelling of the polymer barrier can result in a significant increase in load on the carcass and pressure armour that may compromise the integrity of the pipe. This paper investigates the effect of the volumetric changes in the barrier and how that can influence the extra loading exerted on carcass and pressure armour under service conditions. A simple analytical model has been proposed to predict the extra loading acting on the carcass and the pressure armour. The proposed procedure has been validated using FE results. Experiments have been performed using a three-layer simulated setup and full-scale pipe to investigate the load acting on the carcass and pressure armour. A brief description of the test program and the results are presented. Tests clearly show that there is only a limited increase in hoop stress in the carcass or the pressure armour in pipes immersed in acetone, although the barrier swelled considerably under unconstrained conditions. An empirical procedure has been proposed to account for this swelling retardation behavior. The effect of the PVDF barrier swelling in pressurized supercritical CO2 environments is discussed.