HOW IT’S MADE – Thermoplastic composite pipes made with ambliFibre system

AmbliFibre prototype system with a novel technology developed during the project

Hybrid unbonded flexible pipes with integrated reinforcement layers made of thermoplastic composites are a key technology for the efficient recovery and transport of hydrocarbons at water depths of more than 1,500 metres. Load, pressure and chemical resistance requirements limit the application of conventional riser systems at these water depths. Considering the increasing distance between floating platforms and subsea assemblies, self-weight becomes an issue for highly safety-critical components. In the case of unbonded flexible pipes, the substitution of metal layers such as the pressure armour with thermoplastic composites substantially increases the supportable self-weight due to the high strength-to-weight ratio of these materials. Further characteristics such as corrosion resistance, thermal and pressure resilience as well as durability add to the appeal for the application of thermoplastic composites offshore.

Automated production technology
The tape winding process, also referred to as filament winding, enables the automated and efficient production of consolidated composite parts made of thermoplastic unidirectional fibre-reinforced plastic (FRP) tape in a primary-shaping process without additional curing steps. This eliminates the high investments associated with autoclaves, which also appear impracticable in the continuous production of structures with a length of several kilometres. Another advantage of thermoplastic tape winding is the environmentally-friendly, emission-free nature of the process in comparison with competing thermoset technologies. With the thermoplastic system technology, tapes are fed towards the nip point, where they are subjected to pressure and heat and thus fully consolidated with previous layers in arbitrary, load-optimized layups. Lasers are often employed as heat sources due to their high energy concentration, short response times and excellent controllability.

Automated production technology process of thermoplastic composite pipes

Despite intense development and major breakthroughs regarding industrially-capable system technology, laser-assisted tape winding requires a thorough understanding of the process for the reliable production of safety-critical components. A high variety of control variables interacting with unpredictable process disturbances such as insufficient tape quality mean that significant efforts are required to achieve a reliable process when changing the product design or applied materials.

When manufacturing offshore riser systems, this is a crucial point as quality assurance and process repeatability hold great significance considering the serious consequences of a failure in the field.
In the ambliFibre project, a multinational European consortium made up of industrial companies and research institutes collaborated to enhance the laser-assisted tape winding process to meet the expectations and requirements of the offshore industry and other industrial sectors. The mission of the three-year project, which ended in 2018, was to develop the first online model-based, quality-controlled tape winding process with the objective of increasing its flexibility, reliability and productivity. For this purpose, several new hardware and software modules were developed, tested and validated.

How it’s made:
The ambliFibre system combines thermal and optical models  embedded into an integral process control with novel data mining, laser and quality monitoring technologies. This approach allows for drastically reduced waste while predicting potential failures in order to reduce machine downtimes. The  green focus of the technology is supported by an integral life cycle analysis for the resulting products. In summary, the new system represents a major breakthrough for the continuous and discontinuous production of tubular composite  components such as gas tanks for automotive applications or composite ultra-deep-water risers.

Simulation and adaptive manufacturing
For a widespread adoption of laser-assisted tape winding in the industry, proven global and local simulation and modelling tools are necessary.
Within ambliFibre, this was addressed at the University of Twente by devising a sophisticated simulation tool that combines an optical model for determining the laser irradiation distribution with a thermal model, which derives the temperature distribution in the process zone based on the optical model’s output. Within the optical model, a ray-tracing approach is adopted and reflections on the tape and substrate surfaces are considered for optimum accuracy. Thermal modelling is performed locally in order to achieve the temperature distribution in the nip point area and globally to account for heat development in the thickness direction. During the simulation development, phenomena such as roller deformation, tape overlapping in helical layups and polymer crystallization were considered.

The prediction of the ideal temperature distribution taking into account geometry, material, process parameters and thermal history opens up the possibility for a model-based control influencing the process outcome in real time. Moreover, concepts for a model-predictive control were developed and validated at Fraunhofer IPT.

AmbliFibre project coordinator Martin Schäkel from the Fraunhofer Institute for Production Technology (IPT) in Germany explains:

“Customers can come to our facility in Aachen and see the process in action. From the range of new solutions developed by the multinational consortium, they can select precisely which technologies might fit their specific needs, such as the data mining or laser optics applications. As a research institute, we are of course keen to continue optimising and enhancing the technology with our partners.”

“The automotive sector has a lot of experience with using conventional materials like steel, and relationships with suppliers have been built up over the years. We therefore have to first overcome scepticism within the industry by really addressing their need for efficient mass production, and by demonstrating this in a transparent way.”

“Industry interest was encouraged through public workshops with industrial stakeholders as well as demonstrations of our prototype machinery here in Aachen. We’d now like to adapt the technology to new parts and applications, to see what the full potential is.”

This opens up the possibility of compensating for process inconsistencies and disturbances by adjusting process parameters, such as laser power, several time steps in advance.
To close the control loop, two modules for efficient temperature control and measurement were created. For introducing adaptive laser irradiation into the process, RWTH TOS and Ixun Lasertechnik developed a novel laser optics capable of shaping the gradient of the laser spot.

In this way, either the tape or the substrate can be heated with increased laser intensity.

The resulting temperature distribution is recorded and processed by a high-speed thermal camera developed by New Infrared Technologies. The robust and compact design allows for easy integration in a tape winding system. The processed temperature data are analysed by algorithms in order to extract target input values for the simulation and process control.

Knowledge-based data mining
For the purpose of further ensuring process quality, data mining algorithms were developed and embedded in a smart human-machine interface (HMI) by Video Systems. A relational database structure was created to process and analyse the data generated during the project in systematic winding experiments applying different materials and process parameters. During these trials, which were performed with the winding system at Fraunhofer IPT, parameters such as process temperature and consolidation force were recorded and complemented with results from mechanical tests of the samples. The data mining engine studies correlations and direct effects between process data and mechanical test results, deriving conclusions regarding the direct connection of in-process data with the expected result. In this way, the HMI can give the operator direct feedback regarding the parameter adjustments required before or during the process.

Smart machine interface based on data mining algorithms to give the operators some feedback about the process system.
 

When introducing a new product design, a new winding layup or a new material, the data mining engine and the simulation model offer the potential of significantly reducing the ramp-up times and test runs associated with the processing of fibre-reinforced plastics.

During the lengthy production of risers with kilometres of processed tape, the new tools enable quality assurance with respect to changing process conditions and disturbances.

Inline monitoring for quality control
For direct feedback concerning the process stability, the ambliFibre project also contributed an inline monitoring device for the continuous measurement of consolidation quality. To generate standardised structures in the tape suitable for in-process assessment, FRP tape was modified in a hot embossing process automated by RWTH KEmikro. The embossments were utilized to detect the level of consolidation by evaluating their features after the tape was welded together with subjacent layers. Fraunhofer ILT applied thermography for detecting the embossments directly after the nip point.

Inline moitoring device which can detects the degree of consolidation in the tape. Directly after the tapes are welded together.
 

A machine-learning algorithm was trained during multiple test trials in order to dependably detect the features and evaluate the degree of consolidation. Similar to the data mining engine, it can process new learning data to provide accurate feedback for new materials, process conditions or winding layups.

The inline monitoring device enables real-time feedback regarding the deficiencies that might be caused by insufficient tape quality or incorrect process settings. Through the HMI, the current quality is fed back to the operator, who can adjust or stop the process depending on the level of deviation from ideal process conditions.

A modular system for industrial production
All the new modules were tested and validated within the laser-assisted tape winding system at Fraunhofer IPT. For this purpose, pipe demonstrators were benchmarked by Baker Hughes, a GE company. As an additional application, composite pressure vessels were manufactured and subsequently tested by HBN-Teknik A/S. The results revealed favourable performance by the employed system technology, which was continuously optimised until the end of the project.
The ambliFibre production system includes all the developed hardware and software modules. It was conceptualised and designed by Pultrex in three configurations: continuous production, discontinuous production and a combination of both. For the manufacturing of pipes and riser systems, the continuous system was developed with the tape winding head rotating around the part, which is fed continuously through the winding carousel. In this design, the laser is positioned on the carousel, which facilitates guiding the laser light towards the tape winding head. Depending on the application and winding setups, up to four heads can be mounted on one carousel and multiple carousels can be positioned within the production cell. Electrical power, compressed air and cooling water are supplied via an array of slip rings, which are sealed to prevent ingress and cross contamination.

System design for continuous and discontinuous production
 

The discontinuous system for parts like pressure vessels employs a gantry robot for maximum flexibility. The third configuration, a combined production cell for continuous and discontinuous production, was designed to enable fast and automated changes between both production scenarios. To save redundant investment costs, mechanisms for efficient change of the tape winding head and laser system between both production scenarios were devised. All system configurations feature the tape winding head and associated control unit, which were developed and refined by Fraunhofer IPT. The developments in ambliFibre improved the modularity and flexibility of the production technology, so that a customer-oriented and application-specific solution for tape winding technology and control could be produced.

Life cycle costs
The system development within ambliFibre was supported by a novel reliability and maintenance model by Mach4Lab, which simulates and predicts the machine’s failure states in early design stages and facilitates the selection of a cost-effective maintenance strategy. For this purpose, in-field production and failure data were analysed and reliability and maintainability indicators were derived. Based on these, a maintenance cost model was developed and implemented.

This model evaluates the costs for each maintenance intervention on the machine down to the component level and enables the user to compare different scenarios including corrective and preventive maintenance in order to make optimal choices from the design stage of the tape winding system throughout its operative life. The life cycle cost model can be applied to both continuous and discontinuous tape winding machinery.

The final part
Focusing on the products manufactured with the ambliFibre tape winding system, Life Cycle Engineering assessed the environmental impact and life cycle scenarios. The environmental performance was benchmarked for composite pipes and pressure vessels. The detailed evaluation took into account raw materials, means of transport and manufacturing as well as end-of-life usage. A user-friendly web tool was developed that determines major environmental indicators such as carbon footprint for different life cycle scenarios. With this tool, the potential and efficiency of green production strategies can be assessed and demonstrated.

Pipe liner prototype with multi-layer reinforcement made of thermoplastic fibre reinforced tape
 

Conclusion
The substitution of metals with thermoplastic fibre-reinforced plastics offers great potential for offshore applications, such as riser systems in deep-water applications, as the high strength-to-weight ratio of these materials significantly raises the supportable self-weight of the structure. The composite layers can be manufactured via the automated laser-assisted tape winding process and the ambliFibre project managed to improve the process stability and quality assurance to another level. New simulation and data mining tools open up the possibility of reducing ramp-up times for new production scenarios and reliably controlling the process outcome when coupled with a novel adaptive laser optics and high-speed thermal camera. An additional module monitors the quality of the consolidation between layers during the process and delivers instant feedback to the operator. Models for the assessment of system maintenance strategies and product environmental performance support the creation of a sustainable and dependable system technology and lightweight products. Besides a continuous production system for the manufacturing of pipes, a discontinuous system for components such as pressure vessels and a combined production cell were developed for the industry. The modular approach adopted for the system design allows customers to adapt the manufacturing system for laser-assisted tape winding to fit their application and product.