Thursday, February 4, 2010

Visual Inspection

Visual Inspection is one of the most common NDT methods used to evaluate the condition and provide a better quality of an item. Visual method is easily carried out, inexpensive and usually does not require special equipment. It entails reflected or transmitted light from a test object being imaged with a light-sensitive device, such as the human eye.
Such a testing method requires proper vision, good lighting conditions and the knowledge of what exactly to look for.
Visual Inspection can be enhanced by various methods of inspection ranging from a low power magnifying glass through to borescopes. These devices can also be used with television camera systems. Surface preparation can range from wiping with a cloth to blast cleaning and treatment with chemicals to reveal the surface details.

Figure: Olympus IPLEX FX video endoscope 

Defect on a machine part can grow due to different loads and environmental factors such as sun radiation, corrosion etc. NDT Visual Inspection can sometimes identify where a failure is most likely to occur and identify when a failure has started. Frequent visual inspections allow engineers to detect defects in earlier stages and take necessary action to prevent them. Visual Inspection is often enhanced by other surface methods of inspection, which can identify flaws that are not easily seen by the naked eye.
video borescope inspection

In aircrafts, engineers use borescopes to inspect inside of a gas turbine engine. Opening up an engine usually takes time and money. Additionally, opening up can result unnecessary extra defects. Because of these reasons, engineers invented a device with a tube which has optical lenses and reflectors. That allows the operator to see through small openings, where human face cannot go through. This device is called as a borescope or endoscope. video borescopes are widely used In the modern time, which makes the inspection much easier than in the past. They use high resolution cameras which can be rotated or zoomed by the operator. Also they have many additional good features such as saving the day’s work as a video/picture file, so that the engineer can revise the files later, by using a computer.
Borecope inspection of a gas turbine engine where you can clearly see the destroyed blades

In order to understand this video, it's essential to have some basic knowledge about the design of a gas turbine engine. In the next article I will try to explain how such an engine works :)