Pipe Materials, Installation, and Testing
Core concepts
Know common materials: PVC (SDR ratings), ductile iron, concrete (RCP), vitrified clay, HDPE, and asbestos-cement legacy pipe. Match material to loading, soil, and corrosion environment. SDR is dimension ratio; lower SDR means thicker wall and higher pressure class.
Installation
Bedding and backfill control deflection and load. Proper compaction under haunches supports the pipe. Trench safety (sloping, shoring, spoil placement) ties to the safety domain. Joints must be clean and lubricated; deflection limits (often 5% for flexible pipe) are checked after backfill.
Testing
Two main tests: infiltration/exfiltration (water) and low-pressure air. Air test duration depends on pipe size and length and is set by specification. Deflection testing uses a mandrel sized to the allowable deflection. Vacuum testing is common for manholes. Always test before paving and document results.
Traps
Do not confuse SDR direction (lower = stronger). Do not assume air testing replaces deflection testing; both are required. Watch for questions about testing before or after backfill (deflection after backfill; air/water after installation and backfill per spec).
Rule of thumb
For flexible pipe, verify deflection does not exceed 5% of inside diameter using a mandrel pulled by hand. Air test hold times scale with pipe size and length per the specification table.
Worked example
A 12-inch PVC line is air tested; the spec table gives a hold time based on diameter and length. If the gauge drops, find the leak, repair, and retest rather than accepting a marginal pass.