What Is Bend Testing? Weld Qualification

Bend testing evaluates the ductility and soundness of a welded joint by forcing a machined specimen around a mandrel of a specified diameter. The test exposes the weld root, face, or side to tensile stress, revealing defects such as lack of fusion, incomplete penetration, porosity, and cracks that would otherwise remain hidden. Bend testing is a mandatory part of welding procedure qualification (WPS/PQR) and welder performance qualification under ASME Section IX, API 1104, and EN ISO 15614.

Unlike tensile testing which measures strength, bend testing confirms that the weld is defect-free and ductile enough to deform without cracking.

Bend Test Types

Type	Tension Surface	Specimen Thickness	When Required
Face bend	Weld face (cap side) in tension	Full wall for t <= 10 mm	WPS qualification, t <= 10 mm
Root bend	Weld root in tension	Full wall for t <= 10 mm	WPS qualification, t <= 10 mm
Side bend	Full cross-section in tension	~10 mm slice through wall	WPS qualification, t > 10 mm
Longitudinal face bend	Weld face, along weld axis	Per ASME IX QW-462.3(b)	Dissimilar metal welds, differing yield strengths
Longitudinal root bend	Weld root, along weld axis	Per ASME IX QW-462.3(b)	Dissimilar metal welds

ASME Section IX Requirements

Parameter	ASME IX Specification
Specimen width	~38 mm (1.5 in.) for transverse bends
Specimen length	~152 mm (6 in.) minimum
Bend radius (mandrel)	Depends on material: 2t for CS/LAS, 3t for duplex, 4t for Ni alloys
Bend angle	180 degrees (U-bend around mandrel)
Weld reinforcement	Removed flush with base metal surface
Specimen corners	Rounded to max 3 mm radius to prevent edge cracking

For thickness <= 10 mm: 2 face bends + 2 root bends (4 total). For thickness > 10 mm: 4 side bends.

Acceptance Criteria (ASME IX QW-163)

Criterion	Limit
Open defects on convex surface	No single defect > 3 mm (1/8 in.) in any direction
Sum of all defects	Total length of all defects on convex surface must not exceed 10 mm (3/8 in.)
Corner cracks	Cracks originating at specimen corners are disregarded unless clearly caused by lack of fusion, slag, or other internal defects
Cracks in weld or HAZ	No open defects > 3 mm (1/8 in.)

Common Bend Test Failures

Failure Mode	Root Cause	Prevention
Root crack (root bend)	Incomplete penetration, contamination at root	Proper root gap, clean back-purge, root grinding
Fusion line crack	Lack of sidewall fusion	Correct angle, adequate heat input, proper technique
Porosity opening	Gas entrapment in weld metal	Clean base metal, dry electrodes, proper shielding gas flow
HAZ crack	Excessive hardness, hydrogen embrittlement	Preheat control, low-hydrogen consumables, PWHT
Edge tearing	Specimen corners not radiused	Radius corners to 3 mm per QW-462

Bend Testing vs Other Mechanical Tests

Test	Measures	Destructive?	Standard
Bend test	Ductility and weld soundness	Yes	ASME IX QW-160, ASTM E190
Tensile test	Yield, UTS, elongation	Yes	ASME IX QW-150, ASTM E8
Impact test	Toughness at temperature	Yes	ASTM E23, EN ISO 148-1
Hardness test	Resistance to indentation	Semi (small indent)	ASTM E10, E18, E92
Macro examination	Weld profile and structure	Yes (section cut)	ASME IX QW-183, ASTM E340

Common Mistake

Failing to remove weld reinforcement flush with the base metal before bending. Excess cap or root reinforcement acts as a stress riser during the bend, causing premature cracking that masks what would otherwise be a sound weld. ASME IX QW-462.2 requires reinforcement removal flush with the base metal surface on both sides of transverse specimens.

Bend test results are recorded on the procedure qualification record (PQR) and welder qualification test record (WQTR), filed with mill test certificates in the project quality documentation per the inspection and test plan.

Read the full guide to non-destructive testing