Thermal infrared testing

Thermal infrared testing method can be used on components of civil engineering equipments, mainly to verify thickness of parts or to detect lack in a wall. Infrared thermography is a NDT method that utilizes the fact that all objects above absolute zero emit infrared radiation. Infrared monitoring equipment has been developed which can detect infrared emission and visualize is as a visible image.

The thermograms taken with an infrared camera measure or indicate the temperature distribution at the surface of the object at the time of test. Thus, the presence of discontinuity in engineering components or systems, including concretes that have an effect on the temperature distribution on the surface can be detected by using this technique. Leakages in plant components or short circuit that lead to overheating can easily be detected by this method. The advantages and limitations of the methods are as follows:

Advantages

• • It provides results in the form of two-dimensional image of heat distribution on the test surface.
  • Applicable to all situations as long as there is temperature differences exist on the surface of material
  • Infrared is not hazardous
  • It provides area testing instead of point or line testing

Disadvantages

• Cannot determined the depth of void or other defect in materials including in concrete
• Equipment are expensive
• Require highly skillful and experience operator

Acoustic emission testing

Acoustic emission testing method can be used to inform of breaking risk of parts of civil engineering equipments, mainly metallic parts.

Acoustic emissions are microseismic activities originating from within the test specimen when subjected to an external load. Acoustic emission is caused by local disturbances such as microcracking, dislocation movement, irregular friction etc. In NDT, the acoustic emission is normally applied to for monitoring of cracks repeatedly subjected to external loads.
Crack growth will be accompanied by an emission of high frequency sounds in various directions. By placing several sensors around the crack, monitoring the time of arrival of this signal to the sensor, observing the frequency of the emission and the amplitude of the event, the nature of the microcrack in the material can be quantified.
Acoustic emission sources are determined by calculating the difference in time taken for the wave to arrive at different sensors. The velocity of the waves in the specimen is determined using pulse velocity method. The most notable advantage of this technique is that it provides quantitative information regarding crack behavior and propagation rate. However, such a technique is considered as a very sophisticated method that requires highly qualified personnel.

Leak testing

Leak testing method concerns mostly some components of civil engineering equipments having to contain dangerous or lethal gas, but its use is uneasy. Leakage in engineering components can lead to a disastrous consequence. If it involved poisonous gas it may harm workers in plant.
If it involved highly flammable gas, it could lead to fire. Thus leak testing constitutes one of the most important activities in plant life assessment.
There are many techniques used for leak testing. Tracer techniques that involved injection of radioactive tracer into the system and monitoring it by using a highly sensitive detector has been found successful for leak detection in heat exchangers and piping. Other techniques for leak detection include pressure test, hydrotest, and helium leak test.

Neutron radiography testing

Neutron radiography testing method, to be applied to the verification of hydrogenous components, can be used on some components of civil engineering equipments. New NDT techniques are under development, such as:

• Back diffused radiations
• Ultrasonic or magnetic perturbations
• Barkhausen effect
• Mössbauer effect
• Mirage effect
• Nuclear magnetic resonance