Raman and FT-IR Based Methodology Development to Assess Flexible Pipelines Pressure Barrier Degradation in Offshore Installations of the Oil and Gas Industry

The recommended standard technique for monitoring the degradation of polyamide 12 (PA-12) is viscosimetry, through measurements of inherent viscosity (IV) to obtain the values of Corrected Inherent Viscosity (CIV). The CIV values were used as reference to correlate with Raman and IR results. PA-12 pristine samples and those submitted to ageing in reactors with controlled pressure and supercritical CO₂ conditions were analyzed. The specimens were immersed in mineral water (pH 4.0), at a temperature of 120 °C for a period of up to 45 days. From the Raman spectra the ν_asCH2 vibration at 2924 cm⁻¹ seems to be a sensitive spectral probe of PA-12 hydrolytic degradation, therefore the relative intensity decrease of pristine and aged samples was used to compare RAMAN and CIV results. From FTIR spectra, a variation in the intensity of the bands attributed to the α and γ phases, at ∼ 1560 and 1545 cm⁻¹, respectively, was observed, which might be related to the degradation/ageing of the polymer. After analyzing samples submitted to different ageing conditions, there are good evidences that an analyses protocol of Raman and FTIR give consistent qualitative information on the degradation of PA-12, and therefore, is a new alternative for monitoring the hydrolytic degradation of PA-12, thus eliminating the use of toxic organic solvents, reducing the analysis time and bringing information about the degradation mechanism.

During operation, due to offshore production environment exposure, the sealing barrier of the flexible pipes can be damaged because of polymer chains degradation. There is great interest in understanding the influence of pressure, temperature, fluid composition, and supercritical CO₂ on degradation of flexible pipes sealing barrier materials [1]. Therefore, it is extremely relevant a qualitative study of deleterious effects of each one of the factors mentioned above.

Integrity assessment of polyamides is usually performed via corrected inherent viscosity (CIV). It determines the molar mass index of the polymeric matrix. By monitoring molar mass of polyamide, it is possible to evaluate the material ageing. The results provided by CIV analysis of polyamide samples aged in different experimental conditions established the basis for building reliable models to predict their useful life during service, especially in the oil and gas industry. Despite its excellent accuracy, the CIV experiments involve the use of toxic organic solvents, such as m-cresol. In addition, the CIV results provide information on reductions in molar mass and loss of additives, but do not provide any information on changes in the molecular structure of the polymer during ageing [1]. The use of a spectroscopic technique, such as vibrational spectroscopy (Infrared and Raman), can bring valuable information about the microscopic changes that occur in the polyamide matrix during its degradation.