UL, Underwriters Laboratories, has strict guidelines, requiring us to exactly manufacture according to their specifications. UL 651A*, Continuous Length HDPE Conduit, and UL 1990, Nonmetallic Underground Conduit with Conductors, have four categories of pipe thickness: EPEC A (SDR 17), EPEC B (SDR 13.5), Schedule 40 and Schedule 80. SDR11 is not a wall thickness dimension ratio listed and therefore not allowed within the UL listing.
We understand, especially when used in directional drilling, a heavier pipe is required. In 1 '' diameter through 3' diameter, a schedule 80 pipe will match up very closely to SDR 11 wall thickness and provide the extra pull strength required. Refer to our sizing tables for further information.
*In early 2012, UL has changed the standard numbers for plastic electrical conduit. Previously UL 651B was the standard for Continuous Length HDPE conduit. UL 651A was the standard for PVC and HDPE stick conduit. NOW:
NEMA has just revised their Polyethylene Conduit Specification NEMA TC7. NEMA TC7-2015 has SDR 11 in the specification as well as new standards for pipe stiffness and compression.
The standard pressure rating of pipe is dependent on the type of resin, the diameter to wall thickness ratio, the fluid being transported, and the temperature of the application. (Additionally, in a pipe design, fittings will affect the design pressure required of the pipe.)
The formula for pressure rating is:
PR= 2HDS Ft Af/(DR-1)
In simplest terms if Ft (service temperature) is nominal at 73 degrees F, Ft=1.0. Also, if Af, the pipe environmental application is water, sewage or other fluids not aggressive to HDPE, then Af=1.0.
Thus the equation simplifies to PR=2HDS/(DR-1)
HDS is the Hydrostatic Design Stress. The HDS is a rating assigned by PPI (Plastics Pipe Institute) and HSB (Hydrostatic Stress Board) for specific resins. A PE 3408 resin will have an HDS of 800. A PE 4710 resin will have an HDS of 1000. These resins are listed on the PPI website and TR-4 (Technical Report 4).
So for common SDR pipe, the results are quite easy to compute.
SDR PE 3408 PE 4710
13.5 125 psi 160 psi11 160 psi 200 psi