The Aging of Offshore Polyamides under Services Conditions in Subsea Applications
- Jan Berger (Evonik Services Gmbh) | Juergen Franosch (Evonik Services Gmbh) | Carsten Schuett (Evonik Industries AG) | Andreas Dowe (Evonik Industries AG)
- Document ID
- Offshore Technology Conference
- OTC Brasil, 4-6 October, Rio de Janeiro, Brazil
- Publication Date
- Document Type
- Conference Paper
- 2011. Offshore Technology Conference
- 4.2 Pipelines, Flowlines and Risers, 5.2.1 Phase Behavior and PVT Measurements, 7.1.8 Asset Integrity, 4.3.4 Scale, 4.2.3 Materials and Corrosion, 1.6 Drilling Operations
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Recent offshore deepwater and ultra deepwater projects have to meet new technically challenging demands of ever increasing drilling depths. Up to 2000 m water and some additional 5000 m solid is the aim. Harsher and chemically more aggressive environments are encountered. That means high pressure and heat and for example CO2 in supercritical state. These conditions have an increased impact upon the aging of the materials incorporated. Also contact with various production fluids used during oilfield recovery have to be considered. To investigate how Polyamides in use with flexible pipes perform under these conditions a comprehensive screening test program was started. With respect to conditions and fluids in contact with the material in service state, existing accelerated aging and testing standards appear to be in need of an extension covering the aging of Polyamides under these conditions. Therefore the need arises to design aging methods according to these new demands. This paper deals with new accelerated aging methods for Polyamides with focus on hydrolytic degradation under service conditions. Included is:
- aging under high pressure (up to 500 bar) in deionized water-supercritical CO2 phase equilibrium
- aging in substitute ocean water (ASTM D1141-98) under sour and neutral conditions
- aging of polyamides previously saturated with crude oil hydrocarbons under sour and neutral conditions in deionized water
Also aging due to Methanolysis and Ethanolysis is further analyzed. All samples are tested in various states of aging for elongation at break derived from tensile tests and corrected inherent viscosity (CIV).
All data is achieved in laboratory work and analyzed with respect to the aging conditions. Significant differences compared to standardized Polyamide aging methods are observed. The assumptions concerning hydrolytic degradation are confirmed. Dependencies of elongation at break and CIV on degradation are evaluated.
Significance of subject matter:
The results indicate that supercritical CO2 and ocean water do influence the predicted lifetime of Polyamide components In order to minimize costs caused by untimely pipe exchanges and to maintain safety, these results should be taken into account
for pipe design.
Flowlines, Risers, Umbilicals
In deep sea application, unbonded flexible pipelines offer safe, reliable and efficient production. Up to a temperature of about 90°C, Polyamides are the choice for the barrier layer. The manufacturing of those layers with Polyamides is reliable and reproducable.
The most limiting factor for Polyamides is the aging due to hydrolysis, an effect of water at raised temperatures. API17TR2 describes the testing procedure to determine possible operating temperatures. The results of API 17TR2 tests can be transferred in Arrhenius lifetime curves from which the temperature dependent lifetime of the tested PA12 can be derived.
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