Mon, 22 January, 2024
Research undertaken by the Non-Metallic Innovation Centre (NIC) has been published as a paper in Elsevier’s the Journal of Membrane Science.
The paper, ‘Reduction in the transport of sour gases and hydrocarbons to underlying PE-RT through thin films of PVDF’ was co-authored by Abderrazak Traidia, Bernadette Craster, Jerome Rondin, Abdallah Al Tamimi, bringing together contributions from NIC sponsors Aramco Technologies, Adnoc, and TWI, as well as from NIC Associate Member, Arkema.
The work looked into the use of raised temperature polyethylene (PE-RT) for the conveyancing of sour hydrocarbon fluids in spoolable composite pipe at temperatures above 90 °C. This grade of polyethylene swells on exposure to all hydrocarbons but specifically aromatic hydrocarbons and so there is a requirement to reduce the flux of hydrocarbons and gases into the base PE-RT. One solution available to reduce these fluxes is the use of a multi-material pipe wall, but new experimental methods are required for design and validation while saturated in sour hydrocarbon fluids.
The paper details an investigation into the simultaneous transport of species such as CO2, H2S, CH4, water vapour, and aromatic hydrocarbon vapours through single films of PVDF and PE-RT and multilayer walls of PVDF/tie layer(s)/PE-RT extracted from a built (co-extruded) pipe section.
Measurements were taken in real time with specialise gas chromatographs having been modified for the continuous quantification of all species. Experiments were designed to take place at 93°C with gas pressures of 104 or 250 barg. Tests were run with gas only mixtures (dry tests) as well as with gas caps above a mixture of liquid hydrocarbons and water (wet tests). When possible, transport properties such as diffusion and solubility coefficients were determined from the permeation traces.
Gas permeability was calculated for the base polymers and also the combined multilayer structure and the flow rates estimated for a multilayer specimen using the values measured on individual films were confirmed experimentally. A simple mathematical model was proposed to determine the apparent permeability of the multilayer system and the steady-state concentration profiles across the specimen wall. Specimens were inspected for damage after a final depressurization at 70 bargmin-1.
Post exposure assessment of the laminates showed that the adhesion levels were improved and the failure mode was altered from adhesive to cohesive on ageing. The observations made during these tests is important to industry, highlighting that gas permeation is also happening in multiphase fluids.
In conclusion, NIC has conducted ground-breaking research on reducing the transport of sour gases and hydrocarbons in elevated temperature polyethylene (PE-RT) systems. Collaborative efforts with industry sponsors and members have led to innovative solutions and new experimental methods. Real-time measurements, gas permeability calculations, and post-exposure assessments highlight the practical implications of the study. The NIC's commitment to pushing the boundaries of knowledge reaffirms its position as a leading authority on this critical industry topic.
The paper can be accessed from here: https://doi.org/10.1016/j.memsci.2024.122416
