Overview
EN ISO 8491:2004 (ISO 8491:1998) defines a standardized bend test for full-section metallic tubes of circular cross‑section. The standard specifies the method to determine the ability of tubes to undergo plastic deformation in bending. It is intended primarily for tubes with an outside diameter up to 65 mm, unless a product standard specifies a different range. EN ISO 8491:2004 was adopted by CEN without modification and supersedes older EN provisions for tube bend testing.
Key topics and requirements
- Scope: Bend testing of full‑section circular metallic tubes to assess plastic deformation capacity (OD typically ≤ 65 mm).
- Test principle: Bend a straight tube around a grooved former of specified inside radius (r) until the specified angle of bend (α) is reached.
- Testing equipment:
- Tube‑bending machines designed to prevent section ovality.
- Bend former must have a groove matching the tube outside diameter; groove radius, depth and ovality tolerance affect results.
- Test piece: A straight portion of tube of sufficient length to perform the bend on the machine.
- Procedure and conditions:
- Ambient testing normally between 10 °C and 35 °C; controlled testing at (23 ± 5) °C.
- Ensure full contact between test piece and former over the bend length.
- For welded tubes, the weld is normally positioned at 90° to the plane of bending (neutral axis) unless the product standard states otherwise.
- Interpretation:
- Follow requirements in the relevant product standard where provided.
- If not specified, the tube passes if no cracks are visible without magnification.
- Test report must include at least: reference to ISO 8491, test-piece identification and dimensions, angle α and radius r, weld position (if relevant) and test result.
Applications
- Quality control and mechanical testing of metallic tubes used in piping, structural, automotive and industrial applications.
- Verification of tube ductility and forming performance prior to fabrication or certification.
- Supporting product specifications, supplier acceptance testing and failure analysis for bent tube components.
- Useful where bending performance and resistance to cracking under plastic deformation are critical.
Who uses this standard
- Tube manufacturers and mill test laboratories
- Third‑party inspection and certification bodies
- Design and fabrication engineers specifying tube forming requirements
- Procurement and quality assurance teams responsible for material acceptance
Related standards
- ISO 7438 - Bend test for test pieces taken from tubes as transverse strips (referenced for strip tests).
- EN/ISO product standards for specific tube types may specify applicable radii, angles and acceptance criteria; EN ISO 8491:2004 supersedes earlier EN 10232 provisions for bend testing.
Keywords: EN ISO 8491:2004, ISO 8491, tube bend test, metallic tubes, circular cross‑section, tube‑bending machine, bend radius, mechanical testing of metals.
