A bend test is a destructive test used to obtain, usually qualitative, information about the ability of a metallic material to deform plastically when bent. On welded joints, root, face or side bend tests are used to assess the ductility of the weld and to reveal imperfections in the weld zone. FKT NDT provides bend testing on butt-welded and clad (overlay-welded) specimens.
What Does a Bend Test Show?
The specimen is bent around a former (mandrel) of a specified diameter to a specified angle. The surface in tension is then examined for cracks, open defects or other discontinuities. The test answers questions such as:
- Do the weld metal and heat-affected zone have sufficient ductility?
- Is there lack of penetration or lack of fusion at the root?
- Are pores, slag inclusions or lack of sidewall fusion opened up on the surface or through the section?
A bend test does not give a numerical strength value. Results are generally reported as accept or reject, which complements numerical tests such as the tensile test.
Types of Bend Test
- Face bend: the cap (face) side of the weld is in tension.
- Root bend: the root side of the weld is in tension, used to assess root penetration.
- Side bend: used on thicker sections so that the full weld cross-section can be examined.
- Longitudinal bend: the weld runs along the specimen; can be preferred when weld metal and parent metal properties differ significantly.
Where Is It Used?
- Welding procedure qualification (WPQR)
- Welder qualification (welder certification) tests
- Evaluation of cladding and hardfacing welds
- Checking the formability of metallic materials
Standards
Bend testing is commonly applied according to:
- ISO 5173: Destructive tests on welds in metallic materials – Bend tests
- ISO 7438: Metallic materials – Bend test
- ISO 15614-1 and ISO 9606-1: number of specimens and acceptance criteria in procedure and welder qualification
- ASME Section IX and ASTM E190: guided bend tests for projects working to American codes
How the Test Is Performed
- Specimen preparation: the specimen is cut from the welded test piece to the dimensions in the standard. Weld reinforcement is normally machined flush and the edges are rounded.
- Former selection: the former diameter is taken from the applicable standard based on the material’s elongation and the specimen thickness.
- Bending: the specimen is bent smoothly and continuously to the specified angle, typically 180°.
- Evaluation: the outer surface is visually examined, any discontinuities are measured and compared with the acceptance criteria.
- Reporting: the report records specimen type, dimensions, former diameter, bend angle, observed imperfections and the result.
FAQ
What is the difference between a root bend and a face bend?
It is the surface placed in tension. In a face bend the weld cap is on the outside of the bend; in a root bend the root is. Imperfections on that surface open up.
When is a side bend used?
Side bends are generally used instead of face and root bends on thicker welds, so that the full weld thickness is examined in one specimen.
What causes a bend test to fail?
Acceptance criteria depend on the standard. Under ISO 15614-1, for example, the specimen shall not reveal any single imperfection larger than 3 mm in any direction during testing.
Can a bend test replace radiography?
For some welder qualification cases, the standard allows bend or fracture tests as an alternative to radiographic examination. Which applies depends on the standard and the specification.
To arrange bend testing, contact us with your specimen and standard details and we will prepare a quotation.