Visual inspection is probably the most widely used of all the nondestructive tests. It is simple, easy to apply, quickly carried out and usually low in cost. The basic principle used in visual inspection is to illuminate the test specimen with light and examine the specimen with the eye. In many instances aids are used to assist in the examination.
This method is mainly used i) to magnify defects which can not be detected by the unaided eye, ii) to assist in the inspection of defects and iii) to permit visual checks of areas not accessible to unaided eye.
Visual and Optical tests are carried out in aircraft maintenance with following equipment:
i) Magnifying Glass- Generally consists of a single lens for lower power magnification and double or multiple lenses for higher magnification.
ii) Magnifying Mirror- This one is a concave reflective surface, such as a dental mirror may be used to view restricted areas of aircraft not accessible with a magnifying glass.
iii) Microscope- It is a multiple element magnifier, providing very high power magnification, is used for the inspection of parts removed from the aircraft. Some portable units are also used to evaluate suspected indications found on the aircraft.
iv) Borescope- Borescope is a precision optical instrument with builtin illumination. Borescopes sometimes called 'endoscopes' or 'endoprobes', which consists with superior optical systems and high intensity light sources, some broescopes provides magnification option, zoom controls or accessories.
v) Flexible Fibre Optic Borescop- Permits manipulation of the instrument around camers and through passages with several directional changes. Woven stainless steel sheathings protects the image relay bundle during repeated flexing and manoeuvring. The working lengths are normally 60 to 365 cm with diameters from 3 to 12.5 min.
vi) VideoImagescope- The video Imagescope is similar to a Fibrescope with the exception that video camera and its connections have replaced the image bundle and a TV monitor has replaced the eyepiece. This image may be magnified for precise viewing. The field of vision is up to 90 degree and probe tip has four way articulation. Presently the smallest diameter is 9.5 mm with working length up to 100 feet.
RVI is the inspection of objects or areas usually inaccessible to the eye without disassembling surrounding structures or machinery. It allows inspectors to discover hidden discontinuities before they may cause major problems, e.g. poor welding, surface defects, corrosion pits, general condition, degradation, blockages and foreign materials. RVI equipment penetrates remote places, utilising small openings and sending images directly back to the observer or to a video monitor.
NDTS has the latest videoscope system with digital stereo measuring capability for accurate, three dimensional defect measurement at any target angle. By utilising stereo measurement system area, depth and distance between reference points, particular discontinuities can be measured. The equipment has an insertion tube with maximum length of up to 3.5 m, and external diameter of 6 mm maximum. This is a hand held remote visual inspection system; modular in design so that it can be easily configured to inspect behind walls, small vessels through openings, unreachable areas of vessels, inside ceilings, in and around pipes and machinery, under vehicles and aircraft as well as the ducts work in HVAC systems.