Visual Testing (VT)

Visual Inspection Importance and Applications in Industries

Of the 6 major test methods, Visual & Optical Testing or Inspection method is one of the important Non-destructive testing Method predominantly used in industries during manufacturing and in-service preventive maintenance inspections.

Visual Inspection is an NDT method for detecting large number of surface discontinuities such as surface cracks in almost all product forms, surface porosity, forging laps, forging seams, shrinkage on surfaces of castings, misruns, sand inclusion areas on the surfaces, surface finish of engineering components at various stages.

Visual testing method can also be used for detecting discontinuities in weld joints such as cracks, undercuts, excess reinforcement, underfills, slag, porosity, burn through, weld finish, lack of fusion, misalignment and cleanliness of joints before welding. VT is a vital tool in Welding and fabrication shops to control quality of weld joints and is crucial to identify process errors during fabrication. The testing is a useful method to check the weld joints for cleanliness before welding, during welding and after welding. Even dimensional measurements using micrometres, Vernier, profile gauges, surface finish measuring instruments are considered as visual inspection tools

Visual inspection methods are used in preventive maintenance of engineering process plants and structures such as Petroleum refineries, Cross country pipe lines, process equipments in oil and gas industries, power plants, railways, nuclear installations, transport, automotive and especially aerospace industries. In fact, roughly over 80% of maintenance in aircrafts and Helicopters for both military and civil applications are done using Visual inspection method such as borescopes’ and fiberscopes’ inspection and video zooming cameras. Sewage pipe line and difficult to reach areas inside nuclear power stations, hazardous substances storage and usage areas are frequently inspected using VT method. This not only increases the efficiency of plants and structures but can also eliminate forced shutdowns which are inevitable if not properly monitored using non-destructive testing methods.

Visual testing can be done using direct method or indirect inspection methods. Direct inspection method is carried out using naked eye without much usage of instruments. Adequate lighting level is important to perform the testing and codes standards and specification governing the method and application will specify the requirements and procedures for carrying out the VT test effectively. Indirect or remote visual inspection methods use Borescopes, Fibrescopes, Video cameras, Lenses and other visual aids without reaching the surface.

VT testing method often used as supplement to other methods such as Liquid Penetrant testing or FPI testing in Aerospace, Magnetic particle inspection, Ultrasonic inspection, Eddy current testing and Radiography testing. Especially Eddy current method is used for heat exchanger tubes inspections and weld joints testing uses Visual testing tools to check for surface blemishes and other material damages before disposing the tubes in petroleum refineries.

Visual Testing Training Level I & II Course & Certification


  1. Physical principles of the test

Fundamentals of visual and optical testing, Description of visual and optical testing, Image formation, Light sources, Stroboscopic sources, Light detection and recording, Fluorescence detection, Optical and illumination equipment, Nature of light, Nature of light, Basic laws – characteristics of light, Emissivity and reflectance

  1. Vision

The eye, Formation of an image in the eye, Perception of intensity and colour, Separation ability (resolution), Perception, Vision acuity, Near vision acuity tests, Far vision, Colour vision, Reaction of the eye to excitation, Phototopic vision, Scotopic vision, Distance and relief perception, Perception of contrast and colour, Threshold levels of intensity, Vision defects, Types of blindness

  1. VT Equipment and Accessories

Instruments for illumination, Source of visible radiation, Spectral quality Luminous efficiency of light sources, Classification of light sources, Types of illumination, Sources of non-visible radiations, Machine vision technology, Visual aids, Image transmitting instruments, Optical equipment for monitoring vibration, Temperature indicating materials.

Light Intensity Measurements, Evaluating discontinuities in Cast, Rolled, Forged, Welded and inspection of engineering components


  1. Revision of Level I syllabus
  2. Work Parameters and Conditions

Surface preparation, Observation techniques, Direct visual examination Remote visual examination, Comparison between direct visual inspection & remote visual methods, Illumination conditions dependent on type of surface to be examined & expected defects, Evaluation of visual acuity, calibration of the examination using reference samples, Presentation of results to be used in analysis, documentation and filing, Visual and optical testing procedures

  1. Image Recording

Photographic recording, Replication, Replicating medium, Film digitization and image processing, Image capture and film digitizing

      4.Codes, Standards, Specifications & Procedures

General knowledge & overview of codes & standards, General knowledge of specifications and procedures, Objectives of standardization, Performance of test in accordance with written instructions, Records of operating conditions on test forms, Instructions for testing in special situations

  1. Safety Aspects

Safety and environmental considerations, Safety for visual and optical tests, Industrial safety standards

  1. Visual and optical testing environment

Cleanliness, Texture and reflectance, Lighting for visual tests, Light intensities, Vision in the testing environment, Visual safety recommendations

  1. Applications of visual testing

Applications of visual testing during manufacturing processes, Joining processes, Soldering, Brazing, Oxyfuel gas welding, Resistance welding, Arc welding, Visual tests of metal joints, Acceptance standards, Recording and reporting of visual test results, Visual testing of pumps, Visual testing of valves, Interface of visual testing with other non-destructive testing methods, Visual aspects of liquid penetrant testing, Visual aspect of magnetic particle testing, Visual aspects of radiography, Visual aspects of ultrasonic Testing.

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