TJ-144
Heavy Duty Hydraulic Grips
Heavy duty hydraulic wedge grips hold a constant clamping force on a thick welded coupon as it necks, which a mechanical wedge does not always manage at these loads.
SpecificationsTesting standard
ISO 4136
Destructive tests on welds in metallic materials — Transverse tensile test
Written and technically reviewed by Dak System Inc. engineeringLast reviewed
ISO 4136 pulls a coupon cut across a welded joint until it fails. The tensile strength is one output; where the fracture ran is the other, and often the more important. A break in the parent metal means the weld is stronger than the plate, which is what a welding procedure is qualified to achieve.
At a glance
- Test type
- Tensile — the specimen is pulled apart
- Published by
- ISO
- Edition
- ISO 4136:2022
- Material
- Metals, alloys & welds
- Runs on
- Series 7200 and Series 9000
What the test does
A coupon is cut across a welded joint so that it contains parent metal at both ends, the heat-affected zone on either side, and the weld metal in the middle — three regions in series, all carrying the same load. The weld reinforcement is machined flush unless the specification says otherwise, the coupon is machined to section, and it is pulled to failure in wedge grips. The maximum force gives the tensile strength of the joint, and the position of the fracture relative to the weld centreline is identified and classified as weld metal, heat-affected zone, or parent metal.
What it measures, and why it matters
Two things, and the second is often the more important. The tensile strength is compared against the parent material's specified minimum, because the ordinary requirement on a welded joint is that it be at least as strong as the plate it joins. Where the coupon broke then tells you whether that was achieved by the weld being adequate or merely by the plate being weak. A fracture in the parent metal is the outcome a welding procedure is qualified to produce: it says the joint is not the limiting element. A fracture through the weld or the heat-affected zone is a finding however high the load was.
Specimen
The coupon spans the joint, so it contains three different materials in series — parent metal, heat-affected zone, and weld metal. The test finds the weakest.
- Orientation
- Transverse — across the weldThe weld sits in the middle with parent metal at each end, so all three regions carry the same load.
- Reinforcement
- Machined flush unless the specification says otherwiseExcess weld cap adds section and moves the failure into the parent metal artificially.
- Thickness
- Full plate thickness where possibleA thin slice may miss a defect that lies deeper in the joint.
- Multiple specimens for thick plate
- Through the thicknessA thick joint is welded in passes, and the passes are not identical.
- Surface finish
- Free of machining marks across the width
- Mark the weld centreline before testing
- With a scribeDakAfter fracture it can be genuinely hard to tell a HAZ failure from a weld-metal one, and that distinction is the result.
Where it broke IS the result. A high strength with a fracture through the weld metal is a worse outcome than a lower strength with a fracture in the parent plate, because the second says the joint is not the weak link.
Test speed
- Rate
- As the standard specifies
- Reported
- Tensile strength and fracture location
- Acceptance
- Usually against the parent material's specified minimumThe joint is required to reach the plate's specification, not a separate weld figure.
- Photograph the fracture
- Against the scribed centrelineDak
Calculations
Tensile strength of the jointRm
Rm = Fm / S₀
- Fm
- maximum force, N
- S₀
- original cross-sectional area of the reduced section, mm²
Measured on the machined coupon, not from nominal plate dimensions.
How the test runs
- 01Cut coupons transverse to the weld, with parent metal at each end.
- 02Machine the weld reinforcement flush unless the specification requires otherwise.
- 03Machine the coupon to the specified section and check the surface finish.
- 04Measure the cross-section and record the original area.
- 05Scribe the weld centreline on the coupon.
- 06Fit wedge grips with capacity and face length for the thickness.
- 07Align and pull at the specified rate to failure.
- 08Record the maximum force.
- 09Identify the fracture location relative to the scribed centreline.
- 10Classify it as weld metal, heat-affected zone or parent metal.
- 11Report strength and location together, with the parent specification.
Grips and fixtures for this method
Self-tighteningTJ-15
Universal Parallel Wedge Grips
Universal parallel wedge grips with flat inserts, where the plate thickness and failure load sit within their range.
SpecificationsWhat the report has to contain
- Reference to ISO 4136 and the edition
- Parent material and welding procedure identification
- Coupon orientation, dimensions and original cross-section
- Whether reinforcement was removed
- Where in the thickness the coupon was taken from
- Rate of testing
- Maximum force and tensile strength
- Fracture location, classified
- The parent material's specified minimum for comparison
- Any evidence of lack of fusion or porosity on the fracture face
What the machine must be capable of
Substantial force — a full-thickness plate coupon commonly needs between a hundred and six hundred kilonewtons — with wedge grips of matching capacity and enough face length to hold a thick specimen without slipping as it necks. Hydraulic grips hold their clamping force as the section reduces, which mechanical wedges do not always manage at these loads. The frame needs the daylight for a long coupon and alignment good enough that the load is genuinely axial, since a bending component would bias the fracture toward one face and confuse the location finding that is half the result.
What goes wrong in practice
The most consequential error is reporting a strength without the fracture location, which discards half the information and the more diagnostic half at that. Leaving the reinforcement on is next: it produces parent-metal failures that look like passes and are artefacts of geometry. Failing to scribe the centreline makes the weld-versus-heat-affected-zone distinction a matter of opinion after the event, when the regions are only millimetres apart on a rough fracture face. And taking one coupon from a thick multi-pass joint can pass a weld whose defect sits in a pass the specimen never sampled.
ISO 4136 or ASME BPVC Section IX
| ISO 4136 | ASME BPVC Section IX | |
|---|---|---|
| Purpose | Transverse tensile on a welded joint | Procedure and welder qualification |
| Acceptance | Usually the parent minimum | Specified in the Code |
| Fracture location | Reported and central to the result | Reported |
| Used with | ISO 5173 bend tests | Its own bend and other tests |
Both qualify a joint rather than a material, and both are run alongside bend tests rather than alone. Which framework applies is a contractual question, and a coupon tested to one does not automatically satisfy the other.
Questions we are asked about this test
What is ISO 4136?
It is the ISO transverse tensile test for welds in metallic materials. A coupon is cut across the joint so that parent metal, heat-affected zone and weld metal all carry the same load, and it is pulled to failure. Both the tensile strength and the location of the fracture are reported.
Why does the fracture location matter as much as the load?
Because it tells you whether the weld is the weak link. A fracture in the parent plate means the joint is stronger than the material it joins, which is exactly what a welding procedure is qualified to achieve. A fracture through the weld metal or the heat-affected zone means the joint is the limiting element, and that is a finding regardless of how high the recorded strength was.
Why is the weld reinforcement machined flush?
Because leaving the cap on adds cross-section exactly where the weld is, so the specimen is thicker at the joint than in the parent metal. The failure then migrates into the parent plate for a geometric reason rather than a metallurgical one, and the test stops discriminating. Removing it puts all three regions on equal terms.
What is it compared against?
Normally the parent material's specified minimum tensile strength, not a separate figure for the weld. The requirement on a welded joint is usually that it be at least as strong as the plate, so the acceptance criterion comes from the plate's own specification rather than from this standard.
Why take several specimens through a thick plate?
Because a thick joint is filled in multiple passes, and those passes are not identical — the root, the fill and the cap differ in cooling rate, dilution and microstructure. A single coupon taken from one depth can pass while a defect sits in a pass it never sampled. Multiple specimens through the thickness is how that is covered.
Why scribe the weld centreline before testing?
Because after the fracture it can be genuinely difficult to tell a heat-affected zone failure from one in the weld metal — the regions are millimetres apart and the fracture surface is rough. Since that distinction is the result, marking the centreline beforehand and photographing the break against it is what makes the classification defensible.
Is this run on its own?
Almost never. Transverse tensile answers whether the joint is strong enough; bend tests to ISO 5173 answer whether it is ductile and free of defects, which a tensile coupon can miss entirely. A procedure qualification normally requires both, along with macro examination and often hardness and impact testing.
Running ISO 4136 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 | High — a full-thickness plate coupon commonly needs 100 to 600 kN | 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 | Verified to ASTM E4, and to ISO 7500-1 Class 0.5 |
| Gripping | Wedge grips sized for the plate thickness; the specimen spans the weld with parent metal at each end | Our self-tightening serrated wedge grips, with V-jaws for round specimens, 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.