What DWC pipe is
A double wall corrugated pipe has a corrugated outer wall for strength and a smooth inner wall for flow. Structured wall HDPE piping systems of this type are covered by IS 16098 Part 2, usually in internal diameters from 75 mm up to 1000 mm.
Because it is a gravity pipe, it carries no pressure rating. Its structural specification is ring stiffness, expressed in kN/m² and written as SN.
SN4 versus SN8
SN4 pipe is designed for shallower trenches in areas without heavy vehicle loading — internal drainage, landscaped areas, service runs. SN8 has roughly twice the ring stiffness and is the usual choice for deeper burial, road crossings and anywhere traffic loads reach the pipe.
The trench matters as much as the pipe. A flexible pipe carries load through the surrounding soil, so bedding and side fill compaction are part of the specification, not an afterthought.
Getting the joint right
DWC lines are joined with couplers and elastomeric sealing rings. Check that the ring is seated, the pipe end is clean and the coupler is pushed to the marked depth — most reported infiltration on DWC networks traces back to the joint rather than the pipe.
Specifying a run
- Internal diameter required by the flow calculation
- SN4 or SN8, based on cover depth and traffic loading
- Chamber positions and cover load class at each access point
- Coupler and sealing ring quantity, including for cut lengths