GRP pipes with Hobas centrifugal casting technology

Hobas pipes produced with the Hobas centrifugal casting technology are made of chopped glass fiber, thermosetting resins (e.g. unsaturated polyesters or vinyl ester resins), minerals, and silica sand. The pipes are circular with an even outer diameter.


Hobas pipes with Hobas technology are produced by centrifugal casting in a 100 % computer-controlled process. The manufacturing machine’s arm feeds all raw materials – chopped glass fibers, thermosetting plastics (unsaturated polyester or vinylester resins), and reinforcing agents – into a fast-rotating mold. Layer by layer, in a predefined process, the pipe wall is built up from the outside inwards. The material quantities inserted by the machine are monitored and compared to the desired design values in order to assure that each product is fully traceable with respect to its raw material types and quantities. Once all raw materials have been inserted into the mold, the speed of rotation is increased. High centrifugal forces of up to 75 g press the materials against the mold wall and condense them to a maximum, creating a high quality, very solid and void-free pipe wall. Cold water is used to cool the mold and after the pipe is removed, the pipe ends are trimmed and beveled. Finally, a coupling is mounted onto one end of each pipe.


The centrifugal casting process ensures that the pipes are circular, the wall thickness is uniform over the entire length at exact outer diameter, and the material displays a high longitudinal compressive strength that is particularly important for jacking. Thanks to the three-dimensional chemical bonding of the thermosetting resin, the pipe retains its stability even in very warm environments. The sandwich construction of the wall also ensures that the pipes can withstand high loading without any trouble and enables the pipe’s strength to be customized to suit the specific load directions required.

The figure below shows a typical cross-section of a pipe consisting of a fiber-composite laminate. The raw material compositions of each layer can differ depending on the application. For instance, the thickness of the inner core can be reduced, or the core even removed for higher pressure classes.

Hobas pipe wall structure illustration

1 External protective layer
2 Outer structural layer
3 Transition layer
4 Core layer
5 Transition layer
6 Inner structural layer
7 Barrier layer
8 Inner liner layer

Technical data Hobas pipes with Hobas technology

Main materials resin, glassfibers, sand
Operating temperature -50 °C to +70 °C, higher temperatures may be considered for individual projects
Standard lengths 6 and 3 m, other lengths on request
Pressure range PN 1 – 25
Expected service life more than 150 years
Corrosion protection none needed, as materials used are inherently resistant to corrosion
Hydraulic roughness k = 0.01-0.016 mm (Colebrook-White)
Water jetting resistance tested according to DIN 19523