Electrofusion joining of thermoplastic composite pipes

The oil industry desires to replace steel pipes and connectors for its pipelines, which are prone to corrosion, with thermoplastic composite pipes, which do not suffer from this issue and are lighter and more flexible, so easier to transport and install.
The aim of this research was to design a suitable novel non-metallic connector, utilising electrofusion welding technology, that could be installed on pipelines operating at 65 °C and 100 bar.
In order to achieve this, first the mechanical properties of the thermoplastic composite pipe (TCP) at the desired temperature had to be determined, as this type of material, contrary to more common composites, is poorly covered in literature. A literature review was conducted on the integrity of electrofusion welding and joints to establish the most important design factors. It was also found there was very little literature on finite element modelling of electrofusion joints.
The initial methodology proposed was to computationally model the pipes joined with a commercially-available electrofusion coupler under two loading configurations: in axial tension and hydrostatic conditions. In parallel, the physical tests would be conducted in a laboratory and the data from them would be used to validate the models. However, the tests gave unexpected results and could not be used for validation, but showed that the TCP samples tested were delaminated internally, which enforced major changes on the project and imposed new design factors on the prototype. Preparing the TCPs for the tests included establishing a new method for re-rounding them.
The novel material type required complete characterisation and an extensive custom testing procedure was developed for this purpose, although finally the properties for simulations were obtained using a numerical approach with the help of representative volume element method, validated using the results obtained from the tests. Two coupler prototypes, one novel, were designed and simulated.