Non Destructive Testing

Answer to Question 1

Suggested methods of NDT for surface breaking cracks in the thin aluminium skin of an aircraft.

As the defects that are being searched for are surface defects, the techniques considered were penetrants (dye penetrant testing) and magnetic testing (magnetic particle inspection or eddy current testing). However, as the material being tested (aluminium) is non-ferrous, magnetic particle inspection cannot be applied.

Dye penetrant testing - this test is ideal as it can be easily applied to the skin of the aircraft without removing any of the material from the aircraft. The process would show any cracks that are in the aluminium via the penetrant in the material. The specimen would have to be cleaned quite well as its exposure during service can lead to cracks being contaminated.

Eddy current testing - this test could be used on the aircraft skin, however it is not the most suitable as sheets of aluminium would more than likely have to be removed to allow for the specimen to be tested. As aluminium is a good conductor and non-ferrous (suitable permeability), Eddy current testing would work very well.

Both methods would be effective methods of NDT for this specimen, yet of the two test, dye penetrant testing would be a more suitable test due to its ease of application.

Answer to Question 2

Suggested methods of NDT for sub surface weld defects in a steel pressure vessel. The NDT is to be carried out during construction.

As sub surface defects are searched for, the considered techniques are Radiography and Ultrasonic testing. However, radiography requires access to both sides of the specimen. As the test is during the construction process, it will be assumed that this is possible.

X-ray Radiography - this test will provide adequate detection of the vessel