Thursday, 9 November 2017

Non-Destructive Testing and Inspection

Non-destructive testing (NDT) is a procedure which is a combination of analysis techniques that is used to find out more about the properties of a number of materials, parts, products, welds, or systems without causing any harm to the integrity of the unit while undergoing the test.

NDT laboratories are a great help for a number of industries that includes civil, forensic, mechanical, electrical, systems, aerospace and aeronautical engineering, and even various medical applications.
The two terms namely NDI, non-destructive inspection and NDE or Non-destructive evaluation can help describe the various testing methodology of non-destructive testing.


The Different Kind of NDT Techniques or Inspection
There are various conventional methods of training techniques that have over the year have changed and developed a lot and have become well-documented with different codes, standards, and best practices.  The setup of a conventional technique is rather simple in comparison to advanced methods. Some of the testing methods are as follows,

The Conventional Techniques
  • Acoustic Emission Testing or AET
  • Leak testing or LT
  • Infrared Testing or IR
  • Electromagnetic testing or ET
  • Liquid Penetrant Testing or LPT
  • Magnetic Particle Testing or MPT
  • Radiographic Testing or RT
  • Ultrasonic Testing or UT
  • Film Radiography or FR
  • Vibration Analysis or VA
  • Visual Inspection or VI
  • Straight Beam
Advanced NDT Techniques

Advanced  methods are slightly more difficult to understand as they are emerging technologies and may have certain limitations as they lack technician qualification criteria and no industry codification.

As far as advanced techniques are concerned, only an expert technician can interpret the data, understand the setup and hence cater to such advanced NDT techniques.

Also, there are some methods, which can be further broken down into both conventional and advanced techniques. Like if you consider two forms of ultrasonic testing, for example, straight beam ultrasonic testing (UT) which is a conventional technique used in simple applications and then there is phased array ultrasonic testing (PAUT) which can be regarded as an advanced UT technique.

Advantages of Non-destructive Training over Destructive Training

There is no doubt that NDT boasts of a myriad of advantages over destructive testing. We must first focus on the testing equipment of NDT testing which is often portable and can be performed more than once on a single component.

The component can then be evaluated minutely both externally and internally for any kind of flaws which may prove to be detrimental to the component.

The only disadvantage of NDT is that the results are more qualitative and can be repeated and interpreted differently with varying results by various inspectors.

 The Various Industry Applications of NDT

NDT inspections are a part of a number of industries and that includes the oil and gas and petrochemical industries, along with other industries such as automotive, chemicals, aerospace, and defense. So, the only way to detect and reduce flaws is by including NDT tests.

Some Considerations before Undergoing an NDT Testing

When you plan an NDT inspection, there are four considerations that you must keep in mind,
  • The different types of damage mechanism which has to be inspected for.
  • The orientation of the defect along with the shape and size of the flaw.
  • The location of the defect and whether it is external or internal.
  • The various limitations of the NDT method
Having considered the above factors the operators can optimize the production of facilities and increase both personnel and environmental safety.

Applications of NDT in Aerospace Industry


Non Destructive Testing Applications in Aerospace


Non-Destructive Testing occupied very important role in recent times in industrial applications like Aerospace, aircraft overhaul, automotive, petrochemical and gas, railway, mining, agriculture, power generation, iron, shipbuilding, steel, pipe and tube manufacturing industries etc as a powerful quality tool. Mainly in Aerospace industry in view of high quality requirements safety and stringent Airworthiness requirements. All components are inspected before they are assembled into the aircraft and then they are periodically inspected throughout their useful life.

Most of the inspections done to an aircraft are visual inspections. During heavy maintenance work, much of the interior of the aircraft is stripped out so inspectors can look for damage on the inside surface of the fuselage. Aircraft suffer many types of structural deterioration including corrosion, fatigue, fabrication defects, operation and maintenance, and unforeseen loading. In aircraft maintenance, it is critical to inspect surfaces for any damage that may exist in order to determine the extent of repair work needed, whether that occurs as the result of manufacturing or while the aircraft is in service.


Non-destructive testing (NDT) is one of the quick and most economical ways to perform inspections in Scheduled maintenance and the only way to discover defects that are not visible to the naked eye.

NDT Methods Used in the Aerospace Industry
Several types of non destructive testing methods like liquid penetrant testing, ultrasonic testing, magnetic particle testing and eddy current testing are used to test airplanes.

Liquid Penetrant Testing (LPT)
To reveal the cracks on the surface of airplane, Liquid penetrant testing is one of the most commonly used method in NDT in aerospace industry.

“The fundamental purpose of penetrant testing is to increase the visible contrast between a discontinuity and its background,” said a report on NDT techniques used in the aerospace industry.
Structural damages or surface defects of aircraft materials were observed with LPT. Fluorescent penetrants are used in critical areas for more sensitive evaluation.
Ultrasonic Testing (UT)
The most common sub-surface inspection technique, ultrasonic NDT uses high-frequency sound waves to locate defects under the surface.UT has many uses in the aerospace industry including detection of:

Surface and subsurface defects in welds;
Main structural fittings of landing gear legs and engine attachments;
Aircraft structure joints and pylons;
Bolts located in critical areas;
Adhesive bond quality of lap joints and composite structure;
Thickness measurement after damage or corrosion removal.


Magnetic Particle Testing (MPT)
In magnetic particle testing, fine particles are applied to the surface to monitor magnetic flux. If damage exists, flux “leaks” from the item’s surface, attracting particles to the area.
In the aircraft, MPT is conducted on engines, pumps, landing gear, gearboxes, shafts, and shock struts. It is also widely used for bolt inspection.
Obviously, this task requires trained professionals who are capable of performing a variety of different NDT techniques to get a complete and accurate status of the airplane.
Eddy current Testing (ECT)
In any aerospace maintenance and repair organization Eddy current testing plays an important role.

Eddy current testing is used in Surface Crack Detection on Aluminum alloys
Intersect the inner surface of holes in the component to be inspected.
Automated Inspection of Aircraft Wheels / Wheel Hub / Rotor Disc
Subsurface Corrosion Detection
There is no question that the success of the airplane industry is dependent on NDT. Without NDT, the cost of maintaining and flying in airplanes would increase dramatically, while the safety of flying would decrease. When people step into an airplane they trust that it will get them to their destination with as little turbulence as possible. NDT plays a vital role in keeping air travel one of the safest modes of transportation.