Visual inspection, direct and indirect (VT)
We record the surface condition of equipment, welds and structures by direct observation and, where there is no access or line of sight, with a borescope or videoscope. It is the first method in any inspection plan and the one that yields the most findings per unit of cost.
- Direct and indirect, with borescope and videoscope
- Reference standard: ASME Section V, Article 9
- Inspectors qualified to IRAM-ISO 9712
- Photographic and video record of every indication
VT
Direct and indirect
What is visual inspection?
Visual inspection (VT) assesses the condition of a surface, a welded joint or an enclosure by observation, with or without optical aids. In the direct mode the inspector views the area at close range, with adequate lighting and, where appropriate, with a magnifier, a mirror or a rigid borescope. In the indirect mode a flexible borescope or videoscope reaches the inside of pipework, chambers, heat exchangers, boilers and confined spaces where there is no physical access and no line of sight.
It is the first method in any inspection plan: it runs before ultrasonic testing, magnetic particle testing or liquid penetrant testing because it establishes where deeper examination is needed and with which technique. It is also the method that yields the most findings per unit of cost. It picks up general and localised corrosion, pitting, blistering and coating detachment, surface-breaking cracks, undercut, weld toe defects, spatter and excessive weld reinforcement, distortion, dents, misalignment, loose bolting and leakage at gaskets and flanges.
The outcome depends on three conditions we verify before starting: sufficient lighting on the surface, access to the area to be examined and a qualified inspector. The reference standard is ASME Section V, Article 9, and the personnel performing the test are qualified to IRAM-ISO 9712. The survey is delivered as a report with photographic and video records, the location of every indication and its evaluation against the acceptance criteria applicable to the component.
What visual inspection delivers
The method that opens every inspection plan and sets the order for the ones that follow
Direct and indirect
Close-range observation plus borescope or videoscope where there is no access or line of sight.
First step of the plan
Establishes which areas call for ultrasonic, magnetic particle or penetrant testing, and which do not.
Report with evidence
Photographic and video record of every indication, with its location and its evaluation.
Qualified inspectors
Personnel qualified to IRAM-ISO 9712, working to ASME Section V, Article 9.
Frequently asked questions about visual inspection
What is direct and indirect visual inspection?
Visual inspection (VT) is a non-destructive testing method that assesses the condition of surfaces, welded joints and enclosures by observation. It is direct when the inspector views the area at close range with adequate lighting and aids such as a magnifier or mirror. It is indirect when a borescope or videoscope is used to reach the inside of pipework, chambers, heat exchangers and confined spaces with no physical access or line of sight.
What defects does visual inspection detect?
It detects discontinuities and conditions open to the surface: general and localised corrosion, pitting, blistering and coating detachment, surface-breaking cracks, undercut, weld toe defects, spatter and excessive weld reinforcement, distortion, dents, misalignment, loose bolting and leakage at gaskets, flanges and vents. It does not detect internal discontinuities, which are the domain of ultrasonic or radiographic methods.
When are a borescope or videoscope used?
When the area cannot be viewed directly: the inside of pipework and coils, exchanger tube bundles, boiler chambers, valve bodies, tanks and confined spaces. The borescope or videoscope is introduced through an existing inspection opening and records images and video of the interior without dismantling the equipment or authorising personnel entry.
Which standard applies to visual inspection?
The reference standard for the method is ASME Section V, Article 9, which sets the conditions for performing the test: minimum lighting on the surface, viewing distance and angle, verified resolution and qualification of the inspector. Personnel qualification is evidenced under IRAM-ISO 9712 and, on hydrocarbon tanks and pipework, acceptance criteria are taken from the API standards applicable to the asset.
What conditions are needed to perform the test?
Three: sufficient lighting on the surface to be viewed, access to the area to be examined and a qualified inspector. The surface must be free of dirt, product or scale that would hide the condition of the material. Where lighting or access is missing, portable equipment or a borescope resolves it, and the limitation is stated in the report alongside the scope actually examined.
Related services
Reference standards
- American Society for Nondestructive Testing (ASNT) — international reference on NDT methods and qualification
- IRAM — IRAM-ISO 9712 standard for the qualification of NDT personnel
- American Petroleum Institute (API) — publisher of the API 653, API 1104 and API 579 standards