Overview
ISO 8493:1998 specifies a standardized drift-expanding test for metallic tubes (circular section) to determine their aptitude for plastic deformation by internal expansion. Prepared by ISO/TC 164 (mechanical testing of metals), this second edition replaces ISO 8493:1986 and defines the test principle, apparatus, specimen geometry, operating procedure and minimum reporting requirements for tubes used in product standards.
Key topics and technical requirements
- Scope limits: applicable to tubes with external diameter ≤ 150 mm (≤ 100 mm for light metals) and wall thickness ≤ 10 mm, unless a product standard defines a narrower range.
- Test principle: expand the tube end by pushing a conical mandrel into a specimen until the specified maximum expanded external diameter or percentage expansion is reached.
- Apparatus:
- Variable-speed press or universal testing machine.
- Hardened, polished conical mandrel; preferred cone angles: 30°, 45°, 60°. Mandrel surface hardness and finish must be adequate.
- Specimen geometry:
- Length L ≈ 2D when mandrel cone angle ≤ 30°; L ≈ 1.5D when angle > 30° (D = initial outer diameter).
- Remaining cylindrical length after expansion must be at least 0.5D.
- Ends must be perpendicular to tube axis; edges may be rounded or chamfered.
- Test conditions and procedure:
- Performed generally at ambient temperature 10 °C–35 °C; controlled tests at (23 ± 5) °C.
- Mandrel inserted without shock; axis alignment required; mandrel may be lubricated and must not rotate relative to specimen.
- For dispute resolution, penetration speed ≤ 50 mm/min.
- For welded tubes, internal weld bead may be machined flush; mandrel groove permitted to accommodate weld seam.
- Acceptance criteria & reporting:
- Interpretation as per the relevant product standard. If none, specimen is satisfactory if no visible crack without magnification; minor edge cracking is not cause for rejection.
- Test report should include reference to ISO 8493, specimen ID and dimensions, maximum expanded diameter or percent expansion, mandrel cone angle and test result.
Applications and users
ISO 8493 is used for quality control, product acceptance and material qualification where tube ductility and formability under internal expansion are critical. Typical users:
- Tube manufacturers and suppliers
- Quality assurance and metallurgical laboratories
- Product standards committees and purchasers specifying acceptance testing
- Fabricators assessing suitability for forming/joining operations
Related standards
- Product-specific tube standards (referenced for acceptance limits and mandrel angles)
- ISO/TC 164 publications on mechanical testing of metals
Keywords: ISO 8493:1998, drift-expanding test, tube testing, metallic materials, mandrel, tube ductility test, tube expansion.
