Visual Testing - VT
Visual Inspection is the Process of examination and evaluation of systems and components by use of Human sensory systems aided only by mechanical enhancements to sensory input such as magnifiers, dental picks etc. the Inspection process may be done using such behaviours as looking, listening, feeling, smelling, shaking, and twisting.
Visual testing or VT is the Oldest and most common Non-destructive testing (NDT) techniques. It is typically the first step in the Examination process to inspect a variety of product forms including castings, forgings, machined components and weld elements.
Equipment Required for VT
Visual Testing may be done by direct viewing using line-of-sight vision, or may be enhanced with the use of Optical Instruments such as-
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» Illuminating Lamps.
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The Human eye discerns details carried by reflected light. therefore, it is not only necessary to Magnify details, but to properly Illuminate them. to Make visual inspection, we can use either Direct Daylight or Illuminating Lamps. the lamp shall be capable of providing a Minimum of 50 foot-candles light.
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» Ultraviolet Lamps.
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We need UV Light for highlighting cracks during Dye penetrant and Magnetic particle fluorescent process. Ultraviolet lights shall be capable of providing a minimum of 800 microwatts/cm2 intensity of 365 nanometer wavelength at a distance of 12 inches or at the working distance of the light source, whichever is greater.
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» Optical Borescopes.
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The Borescopes used to inspect the inside surface of the pipe. The best Borescopes is a Video Borescope, also known as Inspection Camera, consisting of a rigid or flexible tube with a miniature video camera at one end. Then end of Insertion tube includes a light which makes it possible to capture video or still images deep within equipment.
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» Magnifying Mirror.
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Inspection Mirror is used to help the user see into difficult or dangerous areas. Some Inspection mirrors can also have light fittings to Illuminate dark areas.
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Compared to Other techniques, visual testing is low in cost and easy to apply and often eliminates the need for further types of testing.
Visual Testing Requirements:
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The Requirements for Visual testing typically pertain to the -
» Vision of the Inspector: Inspector shall have Natural or corrected visual acuity for reading J-2 letters on a Jaeger’s standard test chart at a distance of not less than 12 inches. and can be distinguish and differentiate contrast among color used in the inspection methods performed.
» The Amount of the light falling on the tool which can be measured with a light meter. If we are using direct daylight conditions, it is acceptable. Or if we want to use Illuminating Lamps, the lamps must be able to provide 50 foot-candles lights on the surface of tools.
» The tool must be cleaned properly for inspection.