Whole-tube tensile strength testing evaluates the tensile performance of pipes, tubes, and catheters in their full cross-sectional, as-manufactured configuration, providing essential data for quality control, product certification, and failure analysis. This guide explains the governing standards—including ISO 6259, GB/T 8804, ISO 6892-1, and IEC 60811-501—along with sample requirements, test items, procedures, and acceptance criteria commonly applied by accredited third-party laboratories.
Technical Overview
Whole-tube tensile testing, also known as full-section or integral-tube tension testing, is performed on a complete, uncut length of tube rather than on a machined strip or dumbbell specimen cut from the tube wall. Because the original cross-section, wall thickness distribution, weld lines, surface condition, and extrusion texture of the tube are preserved, the test reflects the true load-bearing capability of the product as installed. This makes it particularly valuable for small-diameter tubing, catheters, hoses, and thin-walled tubes where cutting standard specimens is impractical or would destroy structural features.
The principal standards governing whole-tube tensile strength determination include the ISO 6259 series and GB/T 8804 series for thermoplastic pipes, ISO 6892-1, ASTM E8/E8M, and GB/T 228.1 for metallic tubes, ISO 10555-1 for intravascular catheters, IEC 60811-501 for cable insulation and sheath tubing, and ASTM D380 or ASTM D412 for rubber and elastomeric hose and tubing. Testing is typically carried out in accredited third-party laboratories using calibrated universal testing machines.
Testing Samples
Thermoplastic Pipes and Tubing
Specimens are full straight lengths of PVC-U, PVC-C, PE, PP, PPR, PB, or PVDF pipes and tubing, free from visible defects, taken from production lots in accordance with ISO 6259 or GB/T 8804. Sample length is typically 250 mm to 350 mm, providing sufficient gauge length plus grip engagement. For large-diameter polyolefin pipes where full-section gripping is not feasible, ISO 8513 permits longitudinal strip specimens as a defined alternative, and the test report must state which specimen type was used.
Metallic Tubes
Copper, steel, stainless steel, aluminum, and alloy tubes are tested as full tubular sections per ISO 6892-1, ASTM E8/E8M, or GB/T 228.1, with metal plugs inserted into the gripped ends to prevent grip crushing of thin walls. Product specifications such as ASTM B75 for copper tube and EN 1057 for copper tubes for water and gas define the minimum tensile strength and elongation values that must be verified.
Medical Tubing and Catheters
Intravascular catheters and single-use medical tubing are tested as finished whole-tube sections per ISO 10555-1, which specifies the gauge length between grips and the minimum tensile force that must be withstood, varying with the catheter outer diameter. Silicone, PVC, and polyurethane medical tubing are also frequently evaluated against end-product specifications using full-length sections.
Rubber and Elastomeric Hoses
Flexible hose and elastomeric tubing are tested as full sections or as short full-tube segments in accordance with ASTM D380 and ASTM D412, with capstan or pneumatic grips used to avoid slippage and premature grip failure.
Testing Items
Typical measured and calculated parameters for whole-tube tensile testing include:
- Tensile strength, calculated as the maximum force divided by the original cross-sectional area
- Yield strength and elongation at yield, where applicable to the material
- Elongation at break and force at break
- Tensile modulus, where the standard requires stiffness characterization
- Fracture location and failure mode classification, for example mid-gauge, at-grip, or splitting along weld lines
- Joint pull-out resistance, evaluated separately for assembled systems using dedicated methods such as GB/T 15820 for polyethylene pipe systems
Testing Methods
Specimen Preparation and Conditioning
Specimens are cut to the specified length, deburred where necessary, and conditioned before testing. Plastic tubes are conditioned at 23 °C ± 2 °C and 50 % ± 10 % relative humidity per ISO 291 for a minimum of 40 hours unless the product standard states otherwise. Metallic tube tests are normally performed within the temperature range of 10 °C to 35 °C per ISO 6892-1. Outer diameter, wall thickness, and inner diameter are measured at multiple positions, and the original cross-sectional area A0 is calculated as π/4 × (D2 − d2), or equivalently π × (D − t) × t.
Equipment and Gripping
Testing is conducted on a universal testing machine calibrated per ISO 7500-1 or an equivalent national verification standard, with extensometers meeting ISO 9513 where strain measurement is required. Grip selection is critical: wedge or pneumatic grips with inserted plugs suit rigid tubes, capstan or wrap-around grips suit flexible elastomeric tubing, and dedicated clamps per ISO 10555-1 are used for catheters to avoid cutting or crushing the specimen.
Test Procedure
The specimen is mounted coaxially, a small preload is applied to remove slack, gauge length is marked, and the tube is extended to failure at the constant crosshead speed specified by the governing standard, typically in the range of 5 mm/min to 500 mm/min depending on material and product type. The force-elongation curve is recorded continuously, and tensile strength, yield point, and elongation at break are derived from the curve. If failure occurs at or within the grips, or if the specimen slips, the result is discarded and a retest is performed.
Expression of Results and Acceptance Criteria
Tensile strength is expressed in megapascals and elongation in percent, together with specimen dimensions, test speed, conditioning, number of specimens, and individual and mean values. Acceptance limits come from the applicable product standard: for example, polyethylene pipe standards such as ISO 4427 and EN 12201 commonly require elongation at break of at least 350 %, while EN 1057 specifies minimum tensile strength grades for copper tube. All results must be compared against the limits declared for the specific material grade and size.
Applications
Whole-tube tensile strength testing is applied across a wide range of industries and products:
- Potable water, gas, and industrial thermoplastic piping systems, including PE, PP-R, and PVC pipelines
- Building services and heating installations using PEX and multilayer composite tubing
- Medical devices, including intravascular catheters, IV tubing, drainage tubing, and silicone medical hoses
- HVAC and refrigeration systems using copper tubing to EN 1057 and ASTM B75 requirements
- Automotive fuel lines, brake hoses, and hydraulic hose assemblies
- Wire and cable insulation and sheaths, where IEC 60811-501 permits tubular specimens for tensile verification
- Aerospace, marine, and oil and gas instrumentation tubing made of stainless steel and nickel alloys
FAQ
Question: What is the difference between whole-tube tensile testing and strip specimen testing?
Answer: Whole-tube testing loads the complete, intact cross-section of the product, including weld seams and wall thickness variation, so results represent the actual manufactured article. Strip testing per ISO 8513 removes a longitudinal strip from the pipe wall and is used mainly for large-diameter pipes that cannot be gripped as a full section.
Question: What sample length is required?
Answer: Typical lengths are 250 mm to 350 mm for plastic and metallic tubes, while catheter testing per ISO 10555-1 uses a defined gauge length between grips, commonly 150 mm. The exact requirement is always dictated by the applicable standard and grip type.
Question: What happens if the specimen breaks at the grips?
Answer: Grip failures are treated as invalid. The specimen is retested with adjusted gripping pressure, plug support, or a different grip type until failure occurs within the gauge region.
Question: How are very small or very soft tubes tested?
Answer: Micro-bore tubing is tested with low-force load cells and precision pneumatic or capstan grips, and thin elastomeric tubing may be wound around capstans to distribute stress and prevent slippage.
Question: What information must appear in the test report?
Answer: The report must identify the standard applied, material grade and dimensions, conditioning, test speed, grip type, individual and mean tensile strength and elongation results, failure locations, and a statement of conformity against the specified acceptance criteria.
