Influence of process parameters and manufacturing defects on the properties of thermoplastic composite pipes.

Thermoplastic composite pipes (TCP) have emerged as an innovative solution in the energy industry, offering significant advantages for fluid transportation in offshore and onshore applications. This is because they offer lightweight and non-corrosivity among other benefits in comparison to industrial metallic pipes. However, during the manufacturing of TCP certain defects may be induced in it due to the effects of processing parameters and this can affect the performance of the pipe in the long run with induced defects leading into in-service failures. Among other factors in comparison to thermosets, thermoplastic composites offers a faster, less complex and cleaner processing than thermoset based composite structures. Also, the thermoplastic composite structures can be melted, reshaped, with the potential for reuse and this makes TCP more recyclable and more environmentally friendly than thermoset composite pipes. For the material composition that involves polymer matrix and fibre reinforcement, currently glass and carbon fibres are the reinforcements. Polyvinylidene fluoride (PVDF), Polyether ether ketone (PEEK), Polyamide 12 and high density polyethylene (HDPE) are the matrix. Current techniques such as the filament winding and automated tape laying or placement used in the industry are facing challenges with on-the-spot detection in a continuous manufacturing system. In TCP manufacturing process, the pipe is regularly monitored. When a defect is noticed, the whole process stops, and the appropriate corrective action is taken. However, this is costly and time-consuming exercise and hence, it is vital to decrease the downtime during manufacturing to the barest minimum. The defect formation can occur at different stages of the consolidation process if key manufacturing parameters are not appropriately selected. During the consolidation process, the number of layers and heat distribution influence bonding and void formation. Therefore, higher compaction force improves bonding between layers and reduces void content. However, increased lay-up speed can reduce the overall bonding quality, even with higher force. This necessitates the need to consider a trade off between speed and consolidation temperature as a faster lay-up speeds reduce heat distribution at the nip point, affecting the complete melting and viscosity of the matrix. Post-treatment can enhance surface and mechanical properties. Although the effect of these defects is not fully established, quantifying the effects with the presence of defects will be beneficial. Also, the current in-situ characterization online methods used in monitoring the process provided an outlook on the potential of process monitoring for process optimization and quality control through detecting and classifying these manufacturing defects. This research aims to optimize crystallinity, temperature, and pressure to reduce defects, and enhance product quality. Objectives include reviewing literature, quantifying defects using various techniques, analysing TCP performance under mechanical and thermal conditions, developing sensor-embedded lab-scale consolidation methods, and improving inter-laminar bond strength through optimized parameters. A combination of destructive and non-destructive testing (scanning electron microscopy (SEM), X-ray computed tomograph (XCT), density method and ultra sound) was used in this study to quantifying the defects present in the TCP. The testing and characterization of existing TCP was conducted to benchmark their behaviour, composition, and properties through a series of test and characterization. A series of material characterization and mechanical tests was also conducted. The benchmark properties derived includes that the void content is established to be within 0 to 2.2% with a distribution below 2μm and the tape orientation is deduced to be in ±600 with fibre orientation of ±450 and ±900. The adhesion between the fibre and polyethylene matrix and the layers proved adequate for the performance Both at micro and meso scale. Ultrasonic scan provided interlayer regions but not defects. Hence, factors such as defect geometry, size, distribution, and settings influenced the analysis. Recommend a combination of techniques for defect analysis and confirmation of results with ultrasound test. The matrix of PE and GF was established through Fourier Transform Infrared (FTIR). The thermal stability lies between 200 to 500°C. The crystallinity is influenced by the fibre composition and cooling rate. For non-isothermal behaviour, the Avrami and Mo methods providing insights into the crystallization rate and nucleation effects, although the Ozawa method showed inconsistencies. Therefore, controlling the cooling rate is vital for optimizing the anisotropic properties of the reinforced layer. Through mechanical testing, the mechanical properties, such as pipe stiffness and elastic modulus, were determined to be 2184.2 MPa and 13.18 GPa, respectively. Key failure mechanisms include fibre breakage, delamination from weak interfacial bonding, and microcracking in resin-rich areas. Ultrasonic inspections revealed previously unnoticed internal matrix cracks from the tests. The impact energy absorption capacity is determined to be within the range of 576 KJ/m2 for the top region and 480 KJ/m2 for the bottom region. The study noted a mismatch in thermal expansion coefficients, which can lead to debonding and microleakage in composite structures. Despite the expected increase in thermal conductivity with viscosity reduction, there is contradictions that increase in fibre fraction raise the conductivity. Hence, this thesis presents findings of in-situ characterization of the manufacturing defects of glass fibre reinforced polyethylene matrix for oil and gas industry application by using in-situ consolidation process (vacuum bagging and dual roller methods). For the in-situ process monitoring and characterization, a laboratory scale in-situ consolidation set up was developed and combined with the use of the vacuum bagging technique for the in-house fabrication of laminate parts. The intention is to monitor the manufacturing processing parameters (focused on the temperature and pressure) through the embedment of sensors. This study observed that for the optimization of the consolidation process, especially at 250°C, improved homogeneity and reduced consolidation time, with post-consolidation treatment achieving a 60% reduction in inter-laminar voids and a 9.52% increase in tensile strength. However, higher consolidation temperatures slightly decreased average tensile strength despite reduced void formation. Notable failure modes—intralaminar failure and fibre-matrix debonding is observed, with temperature having a substantial effect on bond strength. Furthermore, the combined effects of these parameters on the sensors are detailed here with a step towards improving the bond strength of the reinforced laminates. Particle Swarm Optimization pinpoints an optimal inter-laminate bond strength of 0.77N/mm under specific conditions. This strategy for the in-situ process monitoring has the potential to retain and improve the integrity of the consolidated part. This will directly improve the quality, production rate and reduction of waste generation of significantly defective TCP.

Author dc:creator

• Okolie, Obinna

Advisor dc:contributor.advisor

• J. Njuguna and N. Faisal

• Thermoplastic composite pipes
• Manufacturing defect quantification
• Manufacturing techniques
• Thermo-mechanical performance
• Damage characterization
• Process monitoring
• Fourier transform infrared
• Fibre composition
• Cooling rate
• Polyvinylidene fluoride (PVDF)
• Polyether ether ketone (PEEK)
• Polyamide 12
• High density polyethylene

Language dc:language

en

Identifier

oai:rgu-repository.worktribe.com:3020613
https://doi.org/10.48526/rgu-wt-3020613

Author Identifier

0000-0001-9221-4441

OAI identifier oai:identifier

oai:rgu-repository.worktribe.com:3020613