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.