What the Flattening Test Evaluates
The test is used as a process and product-quality check for applicable tubular products. It can reveal whether the tube tolerates the required deformation without unacceptable cracking, splitting, lamination or weld separation. The result is relevant to the tested specimen and ordered specification; it does not by itself prove pressure rating, corrosion resistance or fitness for every service condition.
Typical Test Sequence
- Confirm the governing requirement. Review the ordered tube specification and any project-specific test clause.
- Prepare the specimen. Cut and condition the sample without introducing damage that could distort the result.
- Orient the specimen correctly. For welded tube, weld position may be specified because orientation can affect what the test evaluates.
- Apply compression. Flatten the specimen between parallel plates at a controlled rate to the required stage or plate distance.
- Inspect the specimen. Examine the base metal, inside and outside surfaces, edges and weld area where applicable.
- Record the result. Report the standard, specimen identification, dimensions, orientation, final plate distance and observed discontinuities.
Why the Required Plate Distance Varies
Allowable deformation depends on the product specification, outside diameter, wall thickness, material grade and manufacturing method. Some requirements use a formula or a staged test, while others define a fixed relationship to tube dimensions. Using a value copied from a different standard can produce a technically meaningless acceptance decision.
Common Findings and What They May Indicate
| Observation | Possible Significance | Next Check |
|---|---|---|
| Crack in base metal | Insufficient ductility, material discontinuity or specimen damage | Verify specimen preparation, heat/lot identity and required mechanical condition |
| Weld opening or separation | Potential weld-integrity or process issue | Confirm weld orientation, ordered standard and supplementary examination |
| Edge tearing | May result from specimen preparation or severe deformation | Check cut-edge condition and the exact acceptance wording |
| Surface mark without a crack | May be tooling contact rather than material failure | Document location and distinguish indentation from an open discontinuity |
Flattening Test vs Other Tube Tests
A flattening test evaluates deformation behavior and, for applicable welded tube, can help assess weld soundness. It is not a substitute for dimensional inspection, tensile testing, hydrostatic testing, eddy-current testing, corrosion testing or surface examination. The required combination depends on the product standard and service risk.
Buyer Inspection Checklist
- Tube standard and edition, grade and manufacturing route
- Outside diameter, wall thickness and specimen length
- Weld orientation and number of specimens, where applicable
- Required flattening stage, plate distance or governing formula
- Acceptance wording for cracks, splits, laminations and weld separation
- Heat/lot traceability, test report format and witness requirement
- Any supplementary NDT, pressure or corrosion test required separately
Related Tube Selection and Inspection Guides
For material and product-form options, review our stainless steel pipe and tube products. For the next inspection step, see the hydrostatic versus eddy-current test guide and the stainless steel tube ovality guide.
Post time: Nov-05-2026