Qualification of VESTAPE® PA12 for Thermoplastic Composite Pipe in Oil and Gas applications | NewsLIGHT #15 | Evonik

Thermoplastic unidirectional tapes (UD tapes) where carbon fibers are impregnated with nylon 12 (PA12) or polyether ether ketone (PEEK) as a thermoplastic matrix offer a high-performance solution for applications where weakness is simply not acceptable. Whether in pipes for the oil and gas industry or structural components, you can depend on VESTAPE® to hold firmly and reliably against all forces with low water absorption and impressive mechanical properties.

Composites made significant advances in the oil and gas industry for pipes and fluid handling. Lightweight thermoplastic composite pipes (TCPs) are spoolable and cost-effectively transported; they can be installed with smaller ships in fewer vessel days, allow quick termination in the field, and therefore significantly reduce the total installation costs compared with today usually used pipes which are reinforced by metal. PA12 offers numerous advantages such as very good resistance to oil and gas hydrocarbons and corrosive environments, a wide temperature range from arctic conditions to 80°C, well-known and predictable long-term ageing behavior, and a track record in the oil and gas industry. For several years Evonik has been supplying VESTAMID® NRG PA12 extrusion grades for the oil and gas industry. These are API qualified and ideally suited for the PA12 matrix polymer used in VESTAPE®.

For the use of VESTAPE in TCP, a full qualification procedure according to Det Norske Veritas German Lloyd Standard F119 (DNVGL-ST-F119) has been started featuring extensive material and component studies and will be finished in Q1 2020. Material tests have been performed thoroughly with a high number of repetitions assessing the various failure mechanisms for each material the TCPs is made of. The process yielded many of insights in the performance of VESTAPE® PA12 in physically impacting or irreversibly degrading environments containing a standardized combination of various hydrocarbons. These combinations are representative of specific crude oil environments. The physical impact of those environments on PA12-CF material has been assessed by material testing dry and after full saturation. The figure shows the behavior of PA12-CF composite in the representative environment chosen. This data quantifies the performance of the material across its service temperature range for 4 different static failure mechanisms: tension in fiber direction, compression in fiber direction, in-plane shear and interlaminar shear. With this information among others, it is possible to design a TCP over the temperature range for hydrocarbon static service.

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Compared to the temperature, the expected physical impact (softening) of the reference hydrocarbon environment is limited. Therefore, a design working for dry conditions will only need minor modification to be efficient when exposed to crude oil and other hydrocarbons. Based on this data, PA12-CF TCPs can be designed and qualified for handling a large variety of production and service fluids. In addition, extensive stress rupture and fatigue testing in environment before and after chemical ageing is carried out in parallel and the results will be included in the final TCP design also for dynamic applications.