Adjustable spanTJ-124
Three Point Bend Fixture
A three-point bend fixture with adjustable span and the roller diameters the method specifies — span-to-depth ratio is set on the fixture, not assumed.
SpecificationsTesting standard
ASTM E190
Standard Test Method for Guided Bend Test for Ductility of Welds
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ASTM E190 is the guided bend test for weld ductility. A coupon is forced into a jig of defined radius so that the bend geometry is imposed rather than found, and the convex surface is then examined for cracks and open defects against the governing code's acceptance limit.
At a glance
- Test type
- Flexure & bend — the specimen is bent
- Published by
- ASTM
- Edition
- E190-21
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
A coupon is cut transverse to a welded joint, its reinforcement removed flush with the base metal, and its edges rounded. It is then placed in a guided bend jig — a plunger of specified radius forced into a die of specified opening, or a wrap-around former — with the surface of interest facing the tension side, and bent in one continuous movement to the full angle. The convex surface is afterwards examined under magnification for cracks and open defects, and their length judged against the acceptance limit in the code that called up the test.
What it measures, and why it matters
Strictly nothing is measured; the outcome is a judgement on a surface. What the method contributes is comparability. In a free bend the specimen finds its own radius according to how it work-hardens, so two laboratories bending nominally identical coupons impose different strains and reach different verdicts. Guiding the bend fixes the geometry, which is why the plunger radius and die opening are the numbers that belong in the report rather than any force. Weld ductility is then a defensible finding rather than an impression. Wherever a welding procedure or a welder has to be qualified before production starts: pressure vessels and boilers under ASME rules, structural steelwork under the AWS codes, pipelines, and the fabrication of heavy plant. It also appears in production testing, where coupons are welded alongside the real joints using the same procedure and consumables and then bent to confirm that what was qualified in the laboratory is still being achieved on the shop floor. In failure investigation it is used the other way round, to establish whether a joint that cracked in service was ductile enough to begin with.
Coupon and jig
The word guided is the whole point. The jig imposes the curvature, so two laboratories bending the same material get the same strain.
- Face bend
- Weld face on the convex surface
- Root bend
- Weld root on the convex surfaceFinds incomplete penetration, which is the most common serious joint defect.
- Side bend
- Through-thickness slice bent on edgeUsed on thicker sections; exposes every weld pass simultaneously.
- Plunger radius
- Set by the governing code, from the materialA tighter radius is a more severe test. It is not a free choice.
- Reinforcement
- Removed flush with the base metal
- Record the jig dimensions used
- Radius and die openingDakWithout them the report cannot be reproduced, because the severity of the test lives entirely in that geometry.
Nothing here is graded. The coupon meets the code's crack limit or it does not, and the number that matters in the report is the plunger radius rather than any force.
Test speed
- Movement
- Continuous to the full bendStopping and restarting can leave a mark that reads as a defect.
- Examination
- Convex surface, against the code's crack length limit
- Corner tears
- Usually judged separately from face cracksMost codes treat an edge tear differently from a crack in the body of the weld.
- Examine under magnification
- Not by eye aloneDak
Calculations
Outer fibre strainε
Approximately t / (2R + t)
- t
- specimen thickness
- R
- radius of the bend at the inner surface
Not reported by this method, but it is why a tighter plunger radius on a thicker coupon is a much more severe test than the radius alone suggests.
Acceptance—
Maximum permitted crack length on the convex surface
Taken from the governing construction code, not from E190 itself.
How the test runs
- 01Cut coupons transverse to the weld in the specified orientation.
- 02Remove the weld reinforcement flush with the base metal.
- 03Round the coupon edges to remove machining corners.
- 04Take the plunger radius and die opening from the governing code.
- 05Set the guided bend jig to that geometry.
- 06Place the coupon with the correct surface facing the tension side.
- 07Force the plunger through in one continuous movement to the full bend.
- 08Remove the coupon and examine the convex surface under magnification.
- 09Measure the length of any crack or open defect.
- 10Judge face cracks and corner tears against their separate limits.
- 11Report the jig geometry alongside the result.
Grips and fixtures for this method
Uniform momentTJ-165
Four Point Bend Fixture
Four-point loading where the specification calls for it, putting a length of the specimen under constant moment rather than concentrating it under one nose.
SpecificationsWhat the report has to contain
- Reference to ASTM E190 and the edition
- Base metal and welding procedure identification
- Bend orientation — face, root or side
- Coupon thickness and width
- Whether reinforcement was removed
- Plunger radius and die opening used
- The code the jig geometry was taken from
- Condition of the convex surface
- Length and location of any crack or open defect
- The acceptance limit applied, and pass or fail
What the machine must be capable of
Enough force to complete the bend — commonly between five and a hundred kilonewtons depending on section and former size — with the stroke to reach the full angle without repositioning, and a jig holding the plunger radius and die opening the code requires. Force accuracy is less critical here than in most methods, because nothing is calculated from the load; what the frame needs is the stability to drive the plunger straight and the travel to finish the bend in one continuous movement.
What goes wrong in practice
Using a larger plunger radius than the code specifies is the error with the greatest consequence, because it quietly makes the test easier while producing a report that looks identical. Recording the jig geometry is the defence. Sharp coupon edges generate corner tears that are indistinguishable from real defects. Stopping mid-bend leaves a witness mark on the very surface being examined. And inspecting by eye rather than under magnification misses fine root cracks a few millimetres long, which is the defect the test exists to find. A quieter failure is reporting a pass without naming the code the jig geometry came from, which leaves a reader unable to tell whether the coupon met a demanding requirement or a lenient one.
ASTM E190 or ISO 5173
| ASTM E190 | ISO 5173 | |
|---|---|---|
| Family | ASTM | ISO |
| Jig | Plunger and die, or wrap-around | Former between rollers, or wrap-around |
| Bend severity from | The governing construction code | The material's specified elongation |
| Framework | ASME BPVC Section IX, AWS codes | ISO 15614 procedure qualification |
The same examination in two families. Which applies is contractual, and a coupon bent to one does not automatically satisfy the other, because the geometry that sets severity is drawn from different sources.
Questions we are asked about this test
What is ASTM E190?
It is the ASTM guided bend test for the ductility of welds. A coupon cut from a welded joint is forced into a jig of specified radius so that the bend geometry is imposed rather than left to the specimen, and the stretched convex surface is then examined for cracks against the governing code's acceptance limit.
What does guided mean here?
That the curvature is set by the jig, not by the material. In a free bend the specimen finds its own radius, which depends on how it work-hardens, so two laboratories bending nominally identical coupons impose different strains. A plunger and die of fixed dimensions removes that variable, which is what makes the results comparable at all.
Where does the plunger radius come from?
From the governing construction code — ASME BPVC Section IX, an AWS structural code, or the contract — chosen from the base material. It is not a free choice, because it is the single parameter that fixes how severe the test is. A larger radius makes the coupon easier to pass while leaving no trace in the report unless the geometry is recorded, which is why it is recorded.
Which orientation should be used?
Whatever the code specifies. Root bends put the weld root in tension and find incomplete penetration, the most common serious joint defect. Face bends stretch the cap. Side bends take a through-thickness slice and bend it on edge, exposing every weld pass at once, which is why they are used on thicker sections and are the most searching of the three.
Is a corner tear a failure?
Usually judged separately. Most codes distinguish between a crack in the body of the weld, which indicates a real soundness problem, and a tear at the specimen edge, which often originates from a machining corner or an inclusion at the cut face rather than the joint. The two carry different limits, so the report should say which was found.
Why is the bend made in one continuous movement?
Because stopping and restarting can leave a witness mark on the convex surface that is difficult to distinguish from a genuine crack once the coupon is out of the jig. Since the examination afterwards is the entire test, anything that introduces an ambiguous feature onto the surface being examined costs the coupon.
How does this relate to the tensile test on the same joint?
They answer different questions and are run together. A transverse tensile coupon establishes that the joint carries load, but it can pass a weld containing a lack of fusion if enough sound metal remains. Bending forces one surface into large tension so that such a defect opens into a visible crack. Procedure qualification normally requires both.
Running ASTM E190 on the Series 7200 and Series 9000
Dak verifies against whichever standard the method names, and where a class applies our frames sit a class tighter than it asks.
| The method asks for | Dak supplies | |
|---|---|---|
| Capacity | Moderate to high — typically 5 to 100 kN with the former and section | Load cells from 1 kg to 60 ton on the Series 7200, and 0.5 to 100 kN on the Series 9000 |
| Force accuracy | ASTM E4 over the working range | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Guided bend jig — a plunger of specified radius forced into a die, or a wrap-around former | Our bend fixtures, built to the specimen |
| Environment | 23 ± 2 °C standard laboratory atmosphere | 3009 series chambers, −150 °C to +400 °C — temperature only |
This page describes the method as practised. The governing text is the current edition from the issuing body. Tell us what you are testing and we will answer with the machine, the fixture and a quotation.