Although monolithically built the pipe wall must be made of three layers:

1. Resin rich interior coating, highly corrosion proof (0,8- 1,5mm)2. Laminate roving embedded in resin3. Topcoat (0.2 mm)

· a resin rich layer (s) inside to provide water tightness
· a load bearing layer (s) with the highest possible strength and stiffness
· An external resin rich layer with or without reinforcement.

As mentioned above the highest strength is achieved when the fibers are continuous in length and they are separated from the layers of filler to avoid that the fibers are damaged or broken by the sand grains during the manufacturing process or when strained in service. The inner, resin rich, coat must be always reinforced by a surfacing veil to prevent cracking of the resin while the external layer, normally, does not need to be reinforced.

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