GRP Pipes   Jinguang GRP Pipes are manufactured using  filament winding process on computer controlled machines. By adjusting the relative speed of mandrel rotation and glass distribution head movement, helical reinforced layers with different angles can be wound. In order to increase the pipe stiffness, especially on large diameter pipes, silica sand can be added to parallel layers of wall.   Winding Angle   For general considerations it is important to take into account that according to the loading of the system and the pressure class, the glass fibres can be helically wound under a predetermined angle with the axis of the pipe, that can also vary layer by layer according to design between 45to 88 degree  which may confer specific design product characteristics.   Nominal diameter   Nominal size of pipe and fitting is based on internal diameter. The range of available sizes is 40 to 3000 mm.   Nominal pressure classes:   Pipes and fittings are classified according to nominal pressure. Standard pressure classes are 4, 6, 10, 16, bars. Intermediate or higher-pressure classes are considered on request or depending on the design parameters and conditions.   Specific Pipe Stiffness Classes   The standard GRP pipes and fittings produced by Iniziative Industriali are described in detail in the document GRP PIPING PRODUCT LIST.   Nominal lengths   Fittings are manufactured by the hand lay-up, contact molding and spray-up process. In hand lay-up and contact molding processes veil and alternate layers of mat and woven roving saturated with resin are applied on the mold. In spray-up process continuous strand roving is fed through a chopper gun, combined with catalyzed resin, and sprayed onto the mould surface.