Visual Inspection (VI), or visual testing (VT), is the oldest and most basic method of inspection. In its simplest form, visual inspection is the process of examining a component or piece of equipment using one’s naked eye to look for flaws. Optical aids such as illuminators, mirrors, borescopes, etc. can be used to enhance one’s capability of visually inspecting equipment. Cameras, computer systems, and digital image analyzers can also be used to further the capabilities and benefits of visual inspection.
Visual inspection is routinely used for internal and external surface inspection of a variety of equipment types including storage tanks, pressure vessels, piping, and other equipment.
Visual inspection is simple and less technologically advanced compared to other methods. Despite this, it still has several advantages over more high-tech methods. Compared to other methods, it is far more cost effective because there is often no equipment required; just the eyes of a knowledgeable inspector. For similar reasons, it is also one of the easiest inspection techniques to perform.
Visual inspections are generally performed as a precursor to more advanced inspection techniques that are capable of detecting flaws beyond what the human eye can see, such as subsurface cracks.
Advanced Forms of Visual Inspection
Remote Visual Inspection (RVI) is an advanced form of visual inspection that uses various types of videoprobes, video borescopes, remotely operated cameras, robotic crawlers, and other specialized tools in order to remotely examine components. In doing so, the risks associated with confined space entry are considerably reduced.
In recent years, unmanned aerial vehicles (UAVs), commonly known as drones, have seen increased adoption and usage for remote visual inspections of structures that are difficult to reach by traditional means, such as flare stacks, elevated pipe trays, and cooling towers.
Relevant Codes, Standards, and Best Practices
Visual inspection is mentioned across a wide array of codes, standards, and recommended practices. Some examples include:
- API 510, Pressure Vessel Inspection Code (Tenth Edition) states: “The inspector shall be directly involved in the inspection activities, especially visual inspections, which in most cases will require field activities to ensure that procedures and inspection plans are followed but may be assisted in performing inspections by other properly trained and qualified individuals who are not inspectors (e.g. examiners and operating or maintenance personnel).”
- API 570, Piping Inspection Code (Third Edition) states: “An external visual inspection is performed to determine the condition of the outside of piping, insulation systems, painting, and coating systems, and associated hardware; and to check for signs of misalignment, vibration, and leakage.”
- API 653, Tank Inspection, Repair, Alteration, and Reconstruction (Fifth Edition) states: “The external condition of the tank shall be monitored by close visual inspection from the ground on a routine basis.”
- API RP 571, Damage Mechanisms Affecting Fixed Equipment in the Refining Industry (Third Edition) includes visual inspection as a suggested technique in the Inspection and Monitoring section of various damage mechanisms. For example, the Inspection and Monitoring section for amine corrosion states: “Visual inspection (VT) of internal surfaces at flow impingement areas, turbulent flow areas, liquid/vapor interfaces, and weld/heat-affected zones (HAZs) is effective in identifying localized corrosion.”
Training and Certification
As with the other conventional nondestructive testing methods, the American Society for Nondestructive Testing (ASNT) has developed guidelines for in-house qualification of inspectors in their SNT-TC-1A document [1]. It provides educational, experience, and training recommendations for NDT personnel who perform in visual inspections.
References
- 2020, “Recommended Practice No. SNT-TC-1A: Personnel Qualification and Certification in Nondestructive Testing (2020),” ASNT.
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