Lamination
A lamination is a planar separation in rolled plate or pipe parallel to the rolling direction, caused by non-metallic inclusions, gas pockets, or porosity in the original ingot, that opens up during rolling.
Definition
Laminations are mostly parallel to the plate surface and difficult to detect by angle-beam UT. They are best detected by straight-beam (0°) UT thickness scanning, which shows a mid-wall reflection. Laminations rarely affect pressure containment but matter in heavy-wall vessels and in plates that will be welded.
How this damage forms
A planar separation inside rolled plate, parallel to the surface — inclusions and voids flattened during rolling. Benign under membrane stress, consequential at welds and nozzles where through-thickness stress finds it.
How it is detected
Straight-beam UT finds laminations trivially — a mid-wall echo with loss of back-wall. RT largely cannot: the separation presents no thickness change along the beam.
What causes it, and what prevents it
Plate edges to be welded and nozzle areas get lamination checks because a lamination intersecting a weld can open (lamellar tearing risk) or divert an angle beam during later weld examination — a lamination found during service inspection also confuses corrosion mapping by mimicking mid-wall loss.
Codes that govern assessment
Plate ordered to ASTM A435/A578 is scanned at the mill; ASME construction codes require checks at specific weld and nozzle locations.
The common reporting error
Reporting a lamination echo as wall loss during thickness surveys. The corrosion-rate calculation that follows is fiction — the flag is a mid-wall reflector WITH a healthy back-wall still present.
Where Lamination fits in an inspection programme
A term is only useful when it connects to a decision. Lamination appears in written procedures, in technique sheets, and in the records an owner or accreditation body reviews afterwards — which means the way it is defined in your documentation has to match the way it is applied on site. Where the two drift apart, audits find it. Atlantis writes and reviews procedures against the governing codes, trains inspection personnel to apply them, and builds the record-keeping that makes the evidence retrievable years later. Procedure development and code consulting · NDT training and certification · Ask us about your programme.
Related terms
- Lamellar Tearing — Lamellar tearing is a step-like cracking that occurs in the base material beneath a weld in heavy plate, parallel to the rolling plane, caused by through-thickness tensile shrinkage stress acting on non-metallic inclusions.
Further reading
lamellar tearing inspection in heavy forgings
More defect terms
Crack · Lack of Fusion · Lack of Penetration · Slag Inclusion · Porosity · Undercut · Overlap · Burn-Through · Weld Spatter · Hydrogen-Induced Cracking
Where this comes up in practice
Terms like this one appear in three places that matter commercially: the written practice that governs how your personnel are qualified, the procedures and technique sheets that define how an examination is actually performed, and the evidence an auditor or client asks for when they want to know why an inspection was accepted. Getting the terminology right is the easy part; being able to produce the qualification record, the calibration traceability and the procedure revision that applied on the day of the inspection is the part that decides audits.
Atlantis NDT provides NDT training and certification against ASNT SNT-TC-1A and ISO 9712, ASNT Level III consulting for written practices and procedure approval, inspection management software that holds qualification, calibration and procedure-revision evidence in recoverable form, and an asset integrity platform that binds inspection results to the asset they describe. Browse the full NDT glossary or ask a Level III directly.