The Eyes Have It: Visual Inspection is Cornerstone of Non-Destructive Testing
With the advanced capabilities of today’s testing (NDT) tools and technologies, it’s easy to overlook the oldest and simplest form of NDT: visual inspection.
Also known as visual testing (VT), visual inspection is the most fundamental type of non-destructive testing (NDT). For example, boiler inspections performed around the turn of the 20th century relied heavily on visual testing. The method remains a mainstay in many industries today.
Like all forms of NDT, visual inspection evaluates materials, equipment and structures without damaging or changing their structural integrity or functionality. However, visual inspection differs from other NDT methods in that it only identifies defects that are directly visible on the surface.
As the name indicates, visual inspections are done with the naked eye or with the aid of basic tools such as microscopes, magnifying glasses, borescopes and video scopes. Depending on the results of that initial visual inspection, the inspector may recommend additional forms of non-destructive testing, such as ultrasonic testing (UT), radiography (RT), dye penetrant testing (PT) or magnetic particle testing (MT) to detect subsurface anomalies.
VT Industrial Applications
A diverse range of industries routinely rely on visual inspection, including:
- Aerospace
- Chemical Refineries
- Food & Beverage
- Manufacturing
- Maritime Operations
- Mining
- New Building Construction/Structural Steel
- Oil & Gas
- Power & Utilities
- Pharmaceuticals
- R&D
In industrial arenas, visual testing is used to:
- Identify surface defects and discontinuities, including cracks, voids, porosity, leaks, corrosion and misalignments
- Validate that a manufactured item meets dimensional specifications
- Identify shape deviations, surface roughness or patterns
- Evaluate weld quality and material integrity
Specific examples of how VT is used in industry include:
- To detect cracks or corrosion in aerospace engine components
- To locate the source of a pipeline leak
- To seek signs of degradation in bridges, buildings and other structures
- To look for cracks or leaks in power plant pressure vessels
VT Process Overview
VT inspections follow a systematic process to ensure a thorough evaluation and accurate results. Key steps in the VT process include:
- Planning & Preparation: This stage involves defining goals of the inspection; determining if (and which) tools are needed; and sample preparation.
- General Assessment: The inspector begins by performing a broad assessment to screen for potential defects, flaws or anomalies.
- Local Inspection: In the next phase, the inspector may enhance illumination and/or use magnification to take a closer look at potential defects identified in the general assessment.
- Analysis & Reporting: Results of the inspection are documented in detail and any defects are evaluated for compliance with applicable standards and requirements.
VT Certifications & Standards
From bridges and mines to power plants and aerospace components, the consequences of overlooking a structural flaw during a visual inspection could be catastrophic. That’s why visual inspections should be performed by qualified individuals who possess the proper training, knowledge, skills and experience.
According to the American Society of Nondestructive Testing (ASNT) Classroom Training Book: Visual Testing:
“Trained inspectors follow standardized guidelines for illumination, distance, and equipment to ensure accurate results. The quality of the inspection often depends on the inspector’s experience and the conditions under which the inspection is performed.”
Certification helps to ensure VT inspectors are skilled and reliable. And naturally, visual testing requires an inspector to have good eyesight or vision corrected to 20/40.
To become a certified Visual Inspector (VT), an individual must complete rigorous training and pass written and hands-on examinations to demonstrate competency. Annual eye examinations and employer verification are also key to the VT certification process.
VT certification spans different levels, starting with Level 1, which represents basic, entry-level proficiency and requires visual inspections to be performed under supervision. Level 2 VT certification represents an intermediate skill level and allows the inspector to work without direct supervision. Level 3 VT inspectors possess advanced expertise and skill levels that qualify them for procedure development, training and supervision.
According to the ASNT:
“Typically, VT must be performed by a Level II rather than a Level I technician because performance of VT inspection and evaluation often cannot be separated.”
In the United States, the ASNT SNT-TC-1A standard governs NDT personnel qualifications, including VT.
VT guidelines for specific industries and applications are outlined by the International Organization for Standardization (ISO). Following these standards helps companies ensure the quality of materials, components and other assets — and ultimately protect workers and the general public from accidents and mishaps related to structural integrity issues.
Benefits of Visual Testing
Whether performed with the naked eye or aided by cameras, magnifiers and other tools, VT offers a number of benefits:
- Non-Destructive: VT offers a non-invasive assessment that does not alter or damage the test object.
- Speed & Efficacy: When performed by a skilled inspector, VT is a fast and effective means of detecting surface anomalies. With results available almost immediately, companies can make faster decisions and minimize downtime.
- Cost-Effective: Because it requires few tools and little prep time, VT is typically less expensive than other NDT methods. If there is an obvious flaw that can be seen by the naked eye, there is no need to take the time and resources to continue the inspection process.
- Versatility: VT is a convenient, portable inspection method that can be adapted for use with a large variety of materials, structures, applications and industries.
- Complements Other NDT Methods: VT is as a fast, affordable screening mechanism to determine if additional NDT methods are needed. When combined with other methods, VT offers a thorough, accurate evaluation.
Limitations of Visual Inspection
Along with significant benefits, visual testing also has limitations that should be taken into account:
- Only Detects Surface Defects: More advanced NDT techniques are required to identify flaws or discrepancies beneath the surface.
- Subject to Human Error – The human eye is not capable of making precise measurements and can be easily tricked. In addition, factors like fatigue could cause an inspector to miss or misread important details. This is why visual inspections are best paired with other inspection methods.
- Environmental Factors: Accurate inspections can be hindered by environmental factors, such as dim lighting or contamination, and cause an inspector to miss a potential issue.
Why Choose IIA?
Like any other inspection method, visual inspection comes with advantages and disadvantages, but it remains a valuable method that should not be dismissed. Because visual testing is a subjective process — informed by an inspector’s skill and experience —it’s important to partner with an inspection leader like Industrial Inspection & Analysis (IIA).
Along with a team of skilled and certified visual inspectors, our toolkit includes an array of remote visual inspection (RVI) technologies, including drones and intrinsically safe (IS), explosion-proof (EX) cameras, that allow us to perform visual inspections in some of the most hard-to-reach inspection locations.
If you need more detail on a flaw or discrepancies identified in a visual inspection, we can follow up your visual inspection with an array of inspection techniques to provide the answers you need.
Our experience spans decades and industries, making us a trusted provider of visual inspections. When it comes to eagle-eyed visual inspections, all eyes are on IIA.
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