Multilayer pipe structures, such as foam core pipes, are a type of sandwich pipe primarily used for pressure-less applications. This design replaces the rigid honeycomb structure often used in plates with foam in the core. The multilayer approach allows for placing the "right material at the right place," such as using different materials in the core and skin layers.
Foam core pipe is the structured wall pipe type that most closely resembles a standard solid wall pipe. This design offers significant weight savings while maintaining stiffness, as material is moved away from the center of the wall, where it is less effective at resisting bending loads. The core layer often utilizes lower-grade materials, including post-consumer recycled PVC pipe material. Direct addition of fillers, such as CaCO3, can also be incorporated into the core or formulation.
Using recycled materials and fillers in the core contributes to cost reduction and sustainability. The core carries only a fraction of the load compared to the outer layers, making it a suitable location for lower-grade or recycled materials. Replacing polymer with filler or gas (foaming) considerably reduces the amount of Carbon used over the pipe's lifespan. A higher filler level can increase stiffness and potentially allow for a thinner wall or more blowing agent without creating blisters, leading to further cost savings.
Standards for structured wall pipes, like EN13476, ISO 21138, and AS/NZS 1260, specify minimum PVC percentages in the core and skins. For example, EN13476 allows a minimum of 60% PVC in the core and 75% in the skins, while AS/NZS 1260 requires a minimum of 80% PVC. Other standards, such as ASTM F891, JIS 9798, and SANS 1601, are specifically for foam core pipes. Formulations for PVC foam core pipe often include CaCO3 (up to 15-20 phr) to compensate for foam's lower stiffness. Using recycled PVC pipe grade (K67) for foaming presents processing challenges compared to injection moulding grade (K57).
Regional Requirements: Minimum PVC content in core/skins specified by standards like EN13476 (60% core, 75% skin), AS/NZS 1260 (80% core).