This document is the technical note for HP Storm Perforation Patterns. An overview and standard perforation patterns with figures discussed.

Perforated pipe plays an integral role in many applications of dual wall (Type S) HP Storm polypropylene (PP) pipe. Generally, perforated pipe is used to accelerate the removal of subsurface water in soils or to allow storm water to percolate into the soil. Currently, two classifications of perforations are specified in the AASHTO material specifications for PP pipe: Class I, and Class II. The Class II perforation pattern comes standard when perforated pipe is ordered. Class One perforated pipe has limited availability. Both classes are explained in more detail in the AASHTO materials specifications (M330).

Standard Perforation Patterns for AASHTO Class II Perforation is derived from the applicable AASHTO specification. Differences between the specifications are covered in the provided table. Class II perforations shall be located in the outside valleys of the

corrugations, be circular and/or slotted and evenly spaced around the circumference and length of the pipe. The perforations shall be located in the outside valleys of the corrugations. The water inlet area shall be no less than 1.5 in2/ft (30 cm2/m) for pipe diameters 12- through 18-inch (300 - 450 mm) and 2.0 in2/ft (40 cm2/m) for pipe diameters larger than and equal to 24 inches (600 mm). Table 1 represents ADS standard perforation patterns for AASHTO Class II.

Figures are provided to show the AASHTO Class II Perforation Patterns for 12”-18” pipe diameters, 24” pipe diameters, 30” pipe diameters and 36”-60” 24” pipe diameters.