Engineering Reference
How to size CIPP liners by host pipe diameter
Selecting the correct nominal diameter (DN) for a CIPP liner is the foundational engineering decision in any trenchless rehabilitation project. This guide walks through the practical steps for matching liner diameter to host pipe internal diameter (ID), accounting for diameter reduction, manufacturing tolerances, and host pipe ovality.
Step 1 — Measure host pipe ID accurately
Field measurement of host pipe internal diameter must account for:
- Original pipe nominal diameter — the design size, but not necessarily current ID due to corrosion or deposits
- Wall thickness loss — corrosion, abrasion, and chemical attack reduce wall thickness over decades
- Internal deposits — sediment, scale, or root intrusion that survives pretreatment
- Ovality — soil settlement causes circular pipes to deform into ovals; CCTV crawlers measure this
Best practice: take measurements at multiple stations along the segment using calibrated CCTV crawler systems with laser profiling.
Step 2 — Select liner diameter range
CIPP liner diameters available from Huatao:
- UV-CIPP Felt Liner: DN200 – DN2200 mm
- Inversion Dry Felt Tube: DN100 – DN2000 mm
- Flexible Reinforced Tube: DN100 – DN1500 mm (pressure pipelines)
- FIPP Thermoplastic Tube: DN150 – DN1000 mm
- Spiral Wound PVC Tube: DN600 – DN2500 mm (and DN3000 box culverts)
Step 3 — Account for diameter reduction
Every CIPP installation reduces host pipe internal diameter by the cured liner wall thickness. Typical CIPP wall thickness ranges:
- Drainage CIPP: 4-6 mm typical
- Pressure pipeline CIPP: 5-10 mm
- Heavy-duty structural CIPP: 8-12 mm
The smooth interior of cured CIPP often offsets the diameter reduction in hydraulic terms — Manning's roughness coefficient drops from typical concrete values (n=0.013) to CIPP values (n=0.009-0.010), recovering or improving flow capacity despite the slight diameter reduction.
Step 4 — Verify ovality compatibility
Most CIPP systems tolerate up to 5-10% host pipe ovality. For severely deformed pipes, FIPP thermoplastic forming or spiral-wound liners can accommodate more extreme cross-sectional irregularities. Send your CCTV survey data to our engineering team for ovality assessment.
Common diameter selection errors
- Using nominal pipe size rather than measured internal diameter
- Ignoring wall thickness loss in old corroded pipelines
- Failing to verify across multiple stations — diameters often vary along a segment
- Overlooking ovality — severely oval pipes may exceed liner accommodation range
For a project-specific liner sizing recommendation, send your CCTV survey, pipe drawings, and damage assessment to our engineering team.
