Back to search

PETROMAKS2-Stort program petroleum

Flexible Pipe Pressure Liner Life Extension Tool

Alternative title: Verktøy for levetidsforlengelse av trykklag i fleksible rør

Awarded: NOK 2.9 mill.

Project Number:

262510

Project Period:

2017 - 2019

Organisation:

Partner countries:

Flexible pipes are extensively used in offshore oil and gas production. Flexible pipes are complex multi-layered structures including metallic wires, layers of polymers, textiles, fabric tapes and lubricants. The inner liner made of Polyamide 11 (PA11) is one of the most delicate components. Its function is to ensure the sealing of the pipe against the transported fluids at high pressure and temperature. These demanding conditions can degrade the liner composition over time, affecting its mechanical properties and defining the service life of the pipeline. In the Norwegian sector, flexible pipes have been in service for almost 20 years in average, approaching their predicted lifetime. However, this was estimated by the pipeline manufacturers often assuming more demanding operating conditions than experienced during the actual service. This gives the possibility to safely extend their lifetime under the conditions of properly measuring and understanding their current status. There is a significant potential for cost saving and high interest among the oil companies in extending their operational lifetime. The objective of the FlexLinerLife (FLL) project has been to develop a systematic methodology for predicting the end of life for PA11 pressure sheaths. To solve this task, an international consortium was established between Norway and Brazil. Inoceano (BR), 4Subsea (NO) and SINTEF (NO) have a successful history of R&D specific for O&G industries. This was combined with fundamental research carried out at NTNU (NO) and UFRJ (BR). Equinor with operations in both Brazil and Norway, have ensured the evaluation during the project. PA11 undergo chemical degradation (hydrolysis) that break amide bonds reducing the length of the polymer chains. This may eventually lead to loss of ductility. The reduction in chain length is measured by changes in the CIV (Corrected Inherent Viscosity) which is proportional to the average molecular weight. The level of plasticization and fraction of crystallinity also influence the transition to brittleness. High levels of plasticization enable PA11 to maintain ductility to lower CIV levels ensuring longer service lives. The approach in the FLL project has been to develop improved models for determining the transition brittleness as function of CIV, the level of plasticization, crystallinity and the strain rate. A model published by Hochstetter et al., OMAE2007-29645, for prediction of the ductile to brittle transition temperature, has been one of the starting point for the FLL work. One of the main experimental tasks in the FLL project has been to determine the ductile to brittle transition temperature for specimens with different combinations of CIV, level of plasticization and crystallinity. Large numbers of specimens (Single Edge Notch Tensile -SENT) have been generated through controlled ageing and extraction of plasticizer. Tensile testing has been performed in the from -40 to + 20 oC. The results from the testing have been used to investigate the precision of the existing prediction model and implement improvements that ensure a better fit to the experimental data. The new model has been tested against specimens taken from PA11 pressure sheath retrieved after many years of use for oil production. The results from this verification show that model parameters derived for specimens aged in laboratory autoclaves (where specimens are exposed on all sides) are not directly applicable to pressure sheaths in the field. In a flexible pipe the pressure sheath is exposed to the oil and gas on only one side creating property gradients that do not exist in laboratory aged samples. Further work is needed to adapt the model for these exposure conditions. The loss of plasticizer from PA11 has also been investigated in the FLL project since models to predict the level of plasticization will be needed in the future. Laboratory tests have been performed to determine how the distribution of plasticizer evolve with time when leaching out from PA11 specimens submerged in water. Test results have been used to estimate diffusion and mass transfer coefficients. A simplified model to simulate the loss of plasticizer has been established for samples uniformly exposed on all sides. However, further development is needed to establish a model that can be used to predict the loss of plasticizer, and possible re-plasticization by hydrocarbons, for pressure sheaths in the field. The FLL project has significantly enhanced the understanding of how the different ageing processes in PA11 influence the transition to embrittlement. An improved prediction model has been developed and remaining challenges to further refine the methodology have been identified.

Flexible pipes are extensively used for offshore oil and gas production. PA11 is a widely used polymer for pressure barrier in these pipes. The objective of the FlexLinerLife (FLL) project has been to develop a systematic methodology for predicting the end of life for PA11 pressure sheaths. The approach has been to improve state of the art models to predict the transition to brittleness as function of molecular weight, plasticization, crystallinity and strain rate. The work has included laboratory testing, theoretical assessment and simulation. The FLL project has significantly enhanced the understanding of how the different ageing processes in PA11 influence the transition to embrittlement. An improved prediction model has been developed and remaining challenges to further refine the methodology have been identified. An important impact from the project is better awareness of considerations that an operator must make when assessing the useful service life of PA11 pressure sheaths.

Flexible pipes are extensively used for O&G production offshore Norway, Brazil and worldwide. Many of the installed flexible pipes are reaching their predicted lifetime. However, this was estimated in the design phase often assuming more demanding operating conditions than experienced during service. Due to the great number of installed flexible pipes together with the high costs for replacing these pipes, there is a significant potential for cost saving and high interest among the oil companies in extending their service lives. The main objective of the FlexLinerLife project is to develop a systematic methodology, capable of improved accuracy in predictions of safe service life and possible life extension of flexible pipes in service. The focus will be the polymer pressure liner (crucial part for the definition of the pipe lifetime), and understand their degradation mechanisms. This will combine several approaches using experimentally properties, structural simulations and in-service monitoring techniques. In addition the following sub-goals will be achieved: -Increase the level of safety of the current installed flexible pipes through more accurate knowledge of the current degradation status -Better understanding of the degradation and failure mechanisms of the PA11 liner materials -Cooperate with relevant technical societies to evaluate the current regulation according to the project outcome -Develop and calibrate numerical models based on investigations of the degraded PA11 material -Selection of relevant new inspection technologies for the evaluation of the degradation status of in-service flexible pipes The results of FlexLinerLife will reduce the environmental impact of offshore installation reducing the necessity of dismiss and replace flexible pipes still safe to use. In addition, the improved knowledge of the degradation mechanisms will reduce the probability of in-service failures with the consequent possibility of large environmental contamination.

Funding scheme:

PETROMAKS2-Stort program petroleum