Surface & Near-Surface NDT · VT
Visual & Remote Visual Inspection
The first method — and the one that directs all the others.
Visual testing (VT) is the systematic examination of a surface — directly, or remotely with borescopes and cameras — to detect visible defects such as cracks, undercut, misalignment, corrosion and contamination. It is the first NDT method applied on almost every job, and it decides where the other methods look.
The explainer
Watch how it works.
Schematic · loops automatically
1Prepare and light the surface
The surface is cleaned and illumination is verified — defect visibility is a function of light level and angle, so both are controlled, not assumed.
2Examine systematically
The inspector scans on a defined grid and viewing distance, so coverage is complete rather than impressionistic.
3Reach the hidden surfaces
A borescope enters through an access point; articulation steers the tip and the internal surface arrives on screen, magnified.
4Assess against acceptance criteria
Indications are compared with the applicable quality level — for welds, typically ISO 5817 — and measured where cursors or gauges allow.
5Record the evidence
Stills and video become part of the inspection record: repeatable, reviewable and auditable years later.
The physics
Visual inspection is engineered looking. What separates VT from a glance is control of the variables that decide whether a defect is visible at all: illumination level, viewing angle, distance, surface condition and the inspector’s acuity — all of which are specified, checked and recorded on accredited work.
Where the eye cannot go, optics go instead. Rigid and flexible borescopes relay an image from inside nozzles, tubes, vessels and hygienic pipework through lenses or fibre bundles to an eyepiece or camera; modern videoscopes add articulation, measurement cursors and full digital recording. For high-purity pharmaceutical systems, remote inspection of orbital welds verifies root condition without cutting a single joint.
VT is also the method that qualifies the rest of the programme: surface condition assessed visually determines whether penetrant, magnetic particle or ultrasonic examination can proceed, and weld visual acceptance to ISO 5817 quality levels is the baseline every fabrication contract starts from.
Where it earns its keep
Typical applications
- Weld inspection during fabrication and in service
- High-purity borescope examination of orbital welds in pharma pipework
- Internal examination of vessels, exchangers and tube bundles
- Storage tank and structural steelwork condition surveys
Standards & schemes
| Designation | Covers |
|---|---|
| EN ISO 17637 | Visual testing of fusion-welded joints |
| ISO 5817 | Weld quality levels for imperfections — the acceptance benchmark |
| EN 13018 | General principles of visual testing |
Metlab visual and remote-visual inspection is performed by certified NDT personnel and CSWIP-qualified welding inspectors.
Why formalise something as simple as looking?
Because most missed defects are missed for procedural reasons — poor light, wrong angle, incomplete coverage — not because they were invisible. Formal VT controls those variables and produces a record that stands up in an audit, which a walk-past never can.
What can a borescope reach?
Any internal surface with an access point the probe diameter can pass — pipework bores, vessel nozzles, exchanger tubes, gearbox internals. Articulating videoscopes steer around bends, and measurement versions size what they find.
Is visual inspection enough on its own?
For some acceptance criteria, yes — many maintenance decisions rest on competent VT. But VT only sees the surface, so critical welds and pressure boundaries normally pair it with a volumetric method such as UT or radiography.
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