Multilayer pipes

Current industry standards classify two different design types:

Multi-layer Composite Tubing (photo: Uponor)
Multi-layer Composite Tubing (photo: Uponor)

M – Type: multi-layer metal pipe
This type of pipe comprises all design types with a metal middle layer regardless if the middle layer is welded or simply glued together with overlap. Thus, both PP-R pipe stabilized with non-welded aluminum foil, the so-called stabi pipe, as well as the well-known multi-layer composite pipe with welded aluminum middle layer fall into this category.

P – Type: multi-layer plastic pipe
P-type pipe are mainly multi-layer plastic pipe primarily for heating applications made of PE-RT or PE-X with an EVOH bonding layer.

The following material combinations are most commonly used:

  • Inner pipe made of cross-linked Polyethylene, PE-Xa, PE-Xb or  PE-Xc;
  • Outer pipe made of Polyethylene, PE-HD, PE-MD or PE-RT → PE-X / Al / PE
  • Same layer structure but with an outer layer of PE-Xb or PE-Xc → PE-X / Al / PE-X
  • Inner pipe made of Polyethylene raised temperature, PE-RT I or II; Outer pipe made of PE-RT → PE-RT / Al / PE-RT

Aluminum is almost exclusively used for the metal layer. At this, special aluminum alloys are employed for composite pipe because of their appropriate forming, welding and corrosion characteristics. Newly developed, specially tailored sandwich foils are expected to provide additional advantages for the production process and pipe properties. For special cases, steel foils can be used wherein stainless steel alloys are preferred.

Pipe design

  • Standard design with aluminum middle layer
  • Designs with outer aluminum layer, a thick inner pipe, usually with standard dimensions, and with thin coating layer

Welding methods

  • Aluminum layer, straight bead butt-welded with TIG (tungsten inert gas welding) process
  • Aluminum layer, butt-welded straight bead with laser welding process
  • Aluminum layer, straight bead lap welded with ultrasonic or laser welding process

Among others, the designations listed below can be found:

  • multi-layer composite pipe = Mehrschicht- Verbundrohr
  • aluminum-composite pipe = Alu- Verbundrohr
  • metal plastic pipe = MP- Rohr
  • plastic-aluminum-plastic pipe = PAP- Rohr
  • composite pipe = Verbundrohr