Visual inspection is the original nondestructive method and greatly undervalued as a technical discipline. Alone, it is considered an inferior practice compared to the advancements in predictive maintenance (PdM) technologies such as Vibration Analysis, Infrared Thermography (IR), Oil Analysis, and Ultrasonics.
“Visual inspection can use both the unassisted eye and a variety of predictive (PdM) technologies during an inspection to observe the condition of components within an operating system.”
Objectivity is foundational and the cornerstone of visual inspection. When the person(s) performing visual inspection are unable to remain objective and begin to introduce subjectivity (opinions and biases), things go unnoticed. This can be harmful to any maintenance program. Subjectivity can blind you to things you see every day and make you complacent. The most obvious things can be innocently overlooked.
In fact, I notice when auditing a maintenance program, more than half of pump bulbs are missed during visual inspections because people are on autopilot and so accustomed to seeing them that they don’t even notice when one is discolored, low, or even bone dry.
On a personal level of comparison, if you drive down the same street daily and you hit a bump, over time it can become something you expect and ignore. The bump is probably less than a minor annoyance, and hardly worth noting unless you’ve ever sloshed coffee on yourself as a result of the same bump. Otherwise, you probably won’t perceive it exists. This is an example of subjectivity.
To the objective personnel working for the street maintenance and improvement department, the same street bump would be noted as a significant fault in the road, marked, measured, documented, reported, and possibly scheduled for repair if the measurement exceeds tolerances identified by the department.
Another example of objectivity versus subjectivity applies when we consider our personal automobiles. For some, if the car is running and not making noises, it must be alright to drive. Right? But, if we are objective about the car’s ability to operate safely we ask different questions such as how worn are the brake pads, or how much tread is remaining on the tires? These objective questions have a physical measurement and can be referenced in your user’s manual.
There’s no place for subjectivity in the practice of visual inspection. Opinions are subjective and will always differ, but it is easier to rely on objective observations such as a crack that is measured as 2-inches long. There’s no room for opinion about what constitutes 2-inches as this unit of measure is common.
Condition-based monitoring (CBM) visual inspection training and experience are key to using it successfully. Visual inspection relies on the use of all human senses and can also incorporate tools intended to enhance them. One such example may be where nondestructive testing (NDT) uses dye-penetrant inspection (DPI) or liquid-penetrant inspection (LPI) to reveal a crack or fissure. Visual inspection for mechanical seals, for instance, may use a spot meter, IR camera, or thermocouple to help record objective measurements to include within reports documenting findings, and assisting with trending of variations in findings over time. Below is a simple eight question visual inspection checklist for your review.
Visual Inspection quality can be impacted by the Task, Demography, Environment, Organization and Social factors.
Click to view the more in-depth Visual Inspection – 5 Factors Impacting Visual Inspection Quality infographic to enable you to drill down further.