Testing standard
ASTM D2290
Standard Test Method for Apparent Hoop Tensile Strength of Plastic or Reinforced Plastic Pipe
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM D2290 measures the apparent hoop tensile strength of plastic and reinforced plastic pipe. A ring cut from the pipe is fitted over two semicircular disk halves which are then pulled apart, stretching the ring around its circumference. The word apparent is doing real work: bending at the split introduces a stress the calculation ignores.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ASTM
- Edition
- D2290-19a
- Runs on
- Series 7200 and Series 9000
What the test does
A ring is cut from the pipe and machined to leave a reduced section at two diametrically opposite points. The ring is slipped over a pair of semicircular disk halves that together fill its bore, and those halves are attached to the testing frame and pulled apart. As they separate, the ring is stretched around its circumference — loaded in hoop tension, the same direction internal pressure loads a pipe. The reduced sections ensure the ring fails away from the two splits, where the disk halves part company and the ring is bent as well as stretched. Force is recorded to failure.
What it measures, and why it matters
The result is apparent hoop tensile strength, the property that governs how much internal pressure a pipe can contain. For filament-wound reinforced pipe it is close to the point of the product: the winding pattern exists to put fibre in the hoop direction, and this test verifies that the wind angle, fibre content and resin system are delivering the strength intended. Because the specimen is small and the test quick, it is well suited to routine quality control across production batches, where a full pressure test on every batch would be impractical. The word apparent, though, is a genuine limitation and not a formality.
Specimen and split disk
The ring is loaded the way pressure loads a pipe, which is the point. Where the apparatus departs from pressure is at the two splits, and that is where the word apparent comes from.
- Specimen
- A ring cut from the pipe
- Reduced section
- Machined at two diametrically opposite pointsIt forces failure away from the splits, where bending is worst.
- Cut ends
- Square and smooth
- Disk fit
- Close, so the ring is supported around its boreA loose fit lets the ring deform into an oval before it loads.
- Friction at the disk face
- Reduced where the method requiresFriction between ring and disk restrains the hoop strain and inflates the apparent strength.
- Split gap
- Small and equal on both sides
- Check the reduced sections are symmetric
- Before testingDakAn asymmetric pair loads one side first, and the ring fails there at a load that describes the machining.
This is an APPARENT strength. At the two splits the ring is bent as well as stretched, and the calculation accounts only for the tension. The figure is a valid, reproducible comparative property, but it is not the true uniaxial hoop strength of the material.
Test speed
- Crosshead speed
- Commonly around 5 mm/minSet by the specification; reinforced plastics are rate-sensitive so it is reported.
- Load area
- Twice the reduced section areaThe ring carries load on both sides, so two sections are in play. Forgetting the factor of two halves the reported strength.
- Valid failure
- In a reduced section, away from the split
- Note which side failed
- And whether both were similarDak
Calculations
σ = Pmax / (2 × A)
- Pmax
- maximum force, N
- A
- area of ONE reduced section, mm²
The factor of two is because the ring carries the load through two sections in parallel. It is the single most common arithmetic error in this test.
How the test runs
- 01Cut rings from the pipe with square, smooth ends.
- 02Machine two diametrically opposite reduced sections.
- 03Measure the thickness and width of each reduced section.
- 04Check the two sections are symmetric.
- 05Condition to the specification.
- 06Fit the ring over the split disk halves, seating it fully.
- 07Reduce friction at the disk faces where the method requires.
- 08Check the split gaps are small and equal.
- 09Attach the disk halves to the frame and align them.
- 10Pull at the specified speed to failure.
- 11Confirm the failure occurred in a reduced section, away from the split.
- 12Calculate strength using twice the area of one reduced section.
What the report has to contain
- Reference to ASTM D2290 and the edition, and the procedure used
- Pipe identification, material and wind angle for filament-wound products
- Ring dimensions and reduced section dimensions
- Split disk diameter and gap
- Whether and how friction was reduced at the disk faces
- Conditioning and test temperature
- Crosshead speed
- Maximum force and apparent hoop tensile strength
- Failure location on each specimen
- Specimens rejected for failing at the split
- Mean and standard deviation
What the machine must be capable of
Force measurement to ASTM E4 across a range that runs from a few kilonewtons for small thermoplastic rings to over a hundred for heavy filament-wound sections, and a crosshead holding the specified speed. The frame needs enough daylight for the split disk assembly and the pipe diameter being tested. Alignment matters in a particular way here: the two disk halves must separate along the load axis without cocking, since any tilt loads one reduced section more than the other. Where hoop strain or modulus is required rather than strength alone, strain has to be measured on the reduced section itself, because crosshead travel includes the whole disk assembly.
What goes wrong in practice
The dominant error is arithmetic: forgetting that the ring carries load through two sections in parallel and dividing by a single section area, which halves the reported strength. The result still looks plausible, which is what lets it survive. After that come failures at the split, which mean the reduced sections are inadequate or asymmetric and must be rejected rather than reported; and inconsistent friction at the disk face, which restrains hoop strain and inflates the apparent strength by an amount nobody can quantify afterwards. The most consequential misuse is treating an apparent hoop strength as a pressure rating.
Apparent hoop strength or true hoop strength
| ASTM D2290 split disk | Pressurised pipe test | |
|---|---|---|
| Loading | Two disk halves pulled apart | Internal hydrostatic pressure |
| Stress state | Hoop tension plus bending at the splits | Pure biaxial hoop and axial |
| Result | Apparent hoop tensile strength | True hoop strength under pressure |
| Cost and speed | Low, quick, small specimen | High, slow, whole pipe section |
The split disk is a screening and quality-control test, not a substitute for pressure testing. It is repeatable and cheap, which makes it excellent for comparing batches and wind patterns, but a design pressure rating comes from pressure testing.
Questions we are asked about this test
What is ASTM D2290?
It is the ASTM method for the apparent hoop tensile strength of plastic and reinforced plastic pipe. A ring cut from the pipe is fitted over two semicircular disk halves, which are pulled apart so the ring is stretched around its circumference. Reduced sections machined at two opposite points force the failure away from the splits.
Why is the strength called apparent?
Because at the two splits, where the disk halves separate, the ring is bent as well as stretched, and the calculation accounts only for the tension. The bending stress is real but unaccounted for, so the reported figure is not the material's true uniaxial hoop strength. It is a valid, reproducible comparative property — and the word apparent is in the title to stop it being used as anything more.
Why divide by twice the reduced section area?
Because the ring is a closed loop and carries the applied load through two sections in parallel, one on each side. Dividing by a single section area halves the reported strength. It is the most common arithmetic mistake in the test, and because the resulting number is still plausible it can survive a long way into a data set before anyone notices.
Why does friction at the disk face matter?
Because friction between the ring bore and the disk surface restrains the ring from straining freely in the hoop direction. That restraint carries part of the load, so the reduced sections see less than the calculation assumes and the apparent strength comes out high. Where the method calls for friction to be reduced, doing so consistently matters more than the absolute value achieved.
Can I use this instead of a pressure test?
For quality control and comparison, yes; for a pressure rating, no. The split disk is quick, cheap and repeatable, which makes it very good at comparing batches, resin systems and filament wind patterns. But the stress state is not that of a pressurised pipe — there is no axial stress and there is bending at the splits — so a design pressure rating has to come from pressure testing.
My rings keep failing at the split. What do I change?
The reduced sections. Their purpose is to make the ring weakest away from the split, so a failure at the split means they are not reduced enough, or the two are not symmetric, or the split gap is too large. Check that both sections are machined to the same dimensions, and that the gaps on the two sides are small and equal.
Does this work for filament-wound pipe?
It is one of its main uses. Hoop strength is exactly what a filament-wound pressure pipe is designed for, and the split disk is a practical way to verify that the wind angle and resin content are delivering it. The wind angle should be recorded with the result, since a change of a few degrees alters hoop strength considerably and the test is sensitive enough to see it.
Running ASTM D2290 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Moderate to high — a filament-wound GRP ring commonly fails between 10 and 100 kN | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Split disk: two semicircular halves that separate, loading a ring specimen in hoop tension | Wedge, vice-action, pneumatic and hydraulic grips, built to the specimen |
| Environment | Standard laboratory atmosphere unless the specification requires conditioning | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.