Required mandrel diameter for flexible sewer pipe deflection acceptance testing, and the inverse — the deflection a given mandrel actually verifies. Runs entirely offline; inputs persist in this browser via localStorage.
Use limits: The base (average) inside diameter is the whole ballgame, and it comes from the pipe standard's table (accounting for OD and wall tolerances) or the manufacturer's submittal — not from the nominal size, and not from measuring one pipe end with a tape. Where the spec includes a mandrel table, the spec's table governs. Presets below are commonly published D3034 values; verify against the standard edition your spec references.
The base ID is the standard's average ID — nominal OD minus two average walls, adjusted for tolerances — which is why an "8-inch" SDR 35 mandrel at 5% is 7.28 in., not 7.60 in. Using nominal ID oversizes the mandrel and fails good pipe.
Test rules that ride along with the size
Deflection testing is for flexible pipe (PVC, HDPE, some fiberglass) — it's a check on embedment quality, since a flexible pipe deflects to whatever shape its bedding allows.
The mandrel should be rigid, with an odd number of legs (typically 9) so it can't align two legs across a single flat, and pulled by hand — no winches. If it takes a comealong, the pipe fails.
Most specs require the test no sooner than 30 days after backfill (or after final backfill loads are in place) so initial deflection has developed.
Proving ring: verify the mandrel against a proving ring or micrometer before the test — mandrels get dropped and legs get bent.
A failed segment usually means re-excavation and re-compaction of haunching — which is why watching the haunch compaction during installation is cheaper than any mandrel.
Common D3034 SDR 35 base IDs (verify against the referenced edition)
Nominal
Base ID (in)
Mandrel at 5% (in)
6 in
5.742
5.455
8 in
7.665
7.282
10 in
9.563
9.085
12 in
11.361
10.793
15 in
13.898
13.203
For ASTM F679 (large-diameter PVC), profile-wall pipe, and HDPE, pull the base ID from the applicable standard or the manufacturer's submittal — the tables differ by standard and cell class.
References
ASTM D3034 — Type PSM PVC Sewer Pipe and Fittings (dimension tables). https://www.astm.org/
ASTM D2321 — Underground Installation of Thermoplastic Pipe (installation and deflection context).
Contract specifications — governing mandrel table, deflection limit, and test timing.