Quality Magazine

Back to Basics: Keeping an Eye on Quality

July 11, 2012

Discover the benefits of using borescopes for visual inspection.

In the field of nondestructive testing (NDT), the main challenges that inspectors face are accessibility and image resolution. Gaining access to the test site is often a challenge because the access openings for inspection are very small. Furthermore, the twists and turns that need to be navigated and the distance from the opening to the inspection site only compound the problem. Image resolution is also a critical factor for successful inspection. If a hard-to-see blemish, hole or incomplete weld is not detected during the manufacturing or maintenance process, equipment is more likely to fail out in the field-inflicting its toll in downtime, added repair costs and frustration.

The Solution

There are several ways to meet the needs for accessibility and image resolution during NDT, which include borescopes (semi-rigid, flexible and video), liquid penetrant inspection (LPI) and blending borescopes.
Remote visual inspection products, including rigid, semi-rigid, flexible-fiber, and videoscopes are practical and efficient solutions to meet an inspector’s needs. Of those types of borescopes, the semi-rigid type typically offers the best image resolution, while flexible-fiber borescopes enable the best access around corners. In addition, when video or still images for documentation or training purposes are needed, an inspector can use a flexible videoscope or video camera mounted to either a rigid or flexible-fiber borescope.
 
In cases where there may be cracks or surface defects that cannot be detected by the naked eye, LPI can be used. LPI uses a special ultraviolet or a visible-light dye, which is applied to the test surface. Then, either an ultraviolet light or a developer solution is applied (depending on the type of dye), which then enables defects to be clearly seen with the help of a specially designed UV borescope that uses special fibers to transmit the UV light to the inspection area.
 
Sometimes, when a crack or blemish is found, the inspector can use a blending borescope to grind and/or polish the defect right there onsite. A wide range of grinding and polishing tools are available for different applications depending on the type of metal and finish required. This type of on-the-spot repair capability saves an enormous amount of time-and money.

The Results

With borescopes, LPI and blending scopes, an inspector can discover small problems before they become big ones that lead to downtime, equipment failure and product recall. When a flaw is discovered in the field or during routine maintenance, the inspector can easily correct the problem onsite, thereby saving money, increasing productivity and reducing waste.

With borescopes, LPI and blending scopes, an inspector can discover small problems before they become big ones that lead to downtime, equipment failure and product recall. When a flaw is discovered in the field or during routine maintenance, the inspector can easily correct the problem onsite, thereby saving money, increasing productivity and reducing waste.

In a manufacturing application, the staff needed to inspect a weld on the inside of main drive shaft for a gas turbine engine. They use a borescope that is mounted to a table. They then bring the part over the borescope and rotate the part 360 degrees to inspect the weld. They perform this inspection using both white light, then switch to UV to ensure the weld is complete and meets their strict quality control requirements. The UV makes any imperfection in the weld much easier to see.

Other applications include inspection of pipes to ensure they are cleaned between processes. This is common in many industries where the user conveys material through large pipes for processing, which can apply to medical, food, plastics or any other material. These materials will change from time to time, thus the pipes need to be cleaned and inspected to ensure that no material has been left in the pipes. With this type of application we turn to the larger 1 to 1.5 inch diameter pipe camera that has a 100-foot pushable cable. This allows the inspector to clearly view the inside of the pipes to ensure there is no foreign matter left in the pipes between process changes.

Tech Tips

When looking for cracks that are running in line with the fastener row, you can rotate the probe 90 degrees and scan in the same way as a fixed sliding probe.

The Dual Frequency Eddy Current testing technique offers the ability to still use sliding probes to scan over countersink rivets and detect cracks, while filtering out noise from the varying rivet conditions caused by the alodine rivets.

NDT technicians armed with an eddy current instrument and a sliding probe will be able to inspect most aluminum skinned aircraft.