System Maintenance & Performance # 2004 Milan
The last years have seen the emergence of several multi-layer pipe structures based on polyolefin materials (PE 80 – PE 100 – PE-X – PP). The combination of a polyolefin with another functional layer in a multi-layer structure enables taking advantage of the properties of the different components. The advantages of the polyolefin material that one likes to maintain are the low cost, the ease of extrusion, the good short-term and long-term mechanical properties, the flexibility, the weldability, and the feasibility to produce long length as coils. The supplementary advantages one likes to acquire are good barrier properties, good wear and scratch resistance, low friction properties, good resistance to rock impingement, good chemical properties or simply good optical properties. The adhesion between PE and technical polymers like for example polyamide, EVOH, with other polyolefins or with aluminium can be tailor-made to meet specific requirements. An assortment of tools and processes enables controlling the adhesion from very weak (peel-able) to very strong. The selection of the right tie-layer, if any, is crucial. A series of test methods, established or under development, are reviewed. Testing on aged samples is the most appropriate way to evaluate the long-term cohesion properties of multi-layer systems. The improvement of the tolerance of pipes against installation conditions and against severe operating conditions has a very high economical attractiveness seeing the installation cost saving potential. Multi-layer pipes meet this objective. Techniques to evaluate the resistance to point loading, or to notch have permitted to demonstrate the fitness for purpose of superthough PE-based pipes.