There are three methods for manufacturing GRP piping:
- Centrifugal, fixed plug and continuous plug.
Prefabricados Delta has chosen the continuous plug method over the others as we consider it to be the most suitable system for underground, medium-pressure water piping (up to 25 bar).
The advantages compared to the centrifugal method are:
- Allows for the full stiffness range from SN 2500 to 10,000 N/m2.
- Offers better performance in terms of inner pressure or deformation stress loads thanks to its continuous winding.
- Enables longer pipes to be manufactured (up to 12 metres).
Compared to the fixed plug method:
- Continuous plug system is very similar to the fixed plug.
- More suitable for water piping as it allows for piping with the same diameter to be produced in series in a more automated fashion.
- Allows pipes of any length to be made thanks to the plug-in system (sleeves).
Continuous plug system
The system entails winding continuous rovings of fibreglass yarn onto a core while the various components are added.
First the inner layer comprising two sublayers is made, one made with chopped and resin and the other with chopped, roving and resin, which usually have a pre-set thickness.
The next stage is the structural layer, which in turn comprises three sublayers, namely: the inner and outer layers, usually made with chopped, roving and resin, forming a three-ply sandwich with the middle sub-layer, made of mineral filler, chopped, roving and resin. The composition of each sublayer normally has an equal percentage of raw material, but thickness of the inner and outer layers depends on the pressure requirements to be borne by the pipe, whereas the intermediate sublayer (the ‘sandwich filling’), which ultimately determines the thickness of the pipe, depends on the stiffness that needs to be obtained in the pipe.
Finally, the outer layer is applied, which is generally a type of gel coat resin.
Heat is applied to the core plug using an infrared system so that the polyester reaches the required consistency before being transferred.
Once the pipe is off the core, it is supported on mobile trolleys and cut to the desired length (usually 12 metres). Pipe sections are connected by sleeves.
Production capacity depends on the diameter - as an example, for a pipe diameter of 1,000 mm at a nominal pressure 10 bar and stiffness of 5000 N/m2, over 400 metres can be produced in one day.