On April 6, 2001, a tourist visiting Philadelphia took a hand-held sledgehammer and struck the Liberty Bell. The blows of the hammer left five indents on the Liberty Bell. After some close visual inspection, the National Park Services hired a team to conduct non-destructive testing on the Bell.
The Liberty Bell is over 200 years old and is an American treasure. After the incident, the National Park services wanted to be sure that the Bell wasn’t too damaged. The Liberty Bell history is very interesting. Its most notable feature is the long crack on the base of the Bell. It is noted that when the first constructed Liberty Bell rang, it cracked. So it was constructed again only to have a poor tone. On the third attempt, everything seemed to be in order. Then in 1846, wile it was ringing for George Washington’s Birthday, a crack formed and left the Liberty Bell unringable. Since then the Bell has been on display only.
Inspecting the Liberty Bell
So after the incident with the hammer, park rangers wanted to be sure that the crack didn’t change or cause any other damages. NDT specialists evaluated the possible damage and the structural status of the Bell.
The NDT specialists performed radiography and were able to compare the readings with tests from more than 25 years before. Fluorescent penetrant was used in the small area where the Bell was struck by the hammer. They used this to ensure there were no new cracks in the metal. To determine any internal flaws, the NDT specialists used ultrasonic inspection. Eddy current inspection was used to map any cracks on the surface.
With all this data, the NDT team is able to keep tabs on the Liberty Bell. They can keep track of the crack and make sure that it does not damage the Bell anymore than it already has. It was determined that the Bell could be repaired with little evidence to the incident. With NDT, we are now able to keep a piece of history alive for everyone to enjoy.