Non-Destructive Testing Methods and Their Applications

What is Non-Destructive Testing?

Methods for detecting defects without causing physical damage to the material or structure being inspected.

Why is Non-Destructive Testing Preferred?

It allows for the detection of defects without affecting the lifespan of the part or structure, providing cost and time savings.

1. VT- Visual Inspection

Visual inspection is the most basic method of examination. It is carried out using the human eye. It is typically used to detect surface defects, cracks, and other visual imperfections.

Among non-destructive testing methods, visual inspection methods are quite important. Here are a few examples of visual inspection methods:

1. Endoscopy: This method is used for visual inspection in narrow and inaccessible areas such as pipelines, engine cylinders, and tanks. It involves the use of a flexible endoscope containing a camera and light source to visualize the interior parts.

2. Microscopy-Macroscopy: Inspection under a microscope. Using microscopes, very small details of material surfaces and structures can be examined.

3. Thermography: Inspection using thermal imaging techniques. By identifying changes in heat distribution, surface defects and other abnormalities in the material can be detected.

4. Surface Defect Inspection: This involves the visual examination of material surfaces. Using special lighting and visual inspection equipment, cracks, pores, holes, and other defects on the surface can be detected.

These visual inspection techniques are widely used to detect defects on the visible surfaces of materials and structures. However, they can be used in conjunction with other non-destructive testing methods to detect deeper defects.

2. MT- Magnetic Particle Testing

Magnetic particle testing is a non-destructive testing method used to detect surface and near-surface defects in metal parts. Here are the commonly used techniques for magnetic particle testing:

1. Dry Method: In this method, a magnetic field is applied to the surface of the part being tested. Then, iron powders or particles are sprinkled on the surface. The magnetic fields in defective areas cause the particles to move or cluster together, revealing the defects.

2. Wet Method: In the wet method, a magnetic field is applied to the surface of the part, followed by the application of a carrier containing water or a special liquid. The liquid causes the magnetic particles to concentrate at the defects on the surface, making the defects more visible.

3. Prod Method (Spark Test): In this method, an electric current is applied to the surface of the part being tested. The magnetic fields in the areas where the current is applied cause metal particles to detach from the surface and create sparks. The intensity of the sparks increases in defective areas, making the defects more visible.

4. Reversal Method: In this method, the direction of the magnetic field is continuously changed. This allows for better detection of surface defects as the magnetic flux lines in defective areas become more pronounced.

These techniques are commonly used methods for detecting defects during magnetic particle testing. Each technique is selected and applied based on specific application requirements and part characteristics.

3. PT- Liquid Penetrant Testing

Penetrant testing (liquid penetrant inspection) is a non-destructive testing method used to detect surface defects. Here are the commonly used techniques for penetrant testing:

1. Spray Method: In this method, a penetrant spray is applied to the surface of the part being tested. The penetrant seeps into the defects on the surface. Then, the excess penetrant is removed from the surface and a developer is applied. Defects become visible as the developer absorbs the penetrant in contact with the defects.

2. Immersion Method: In this method, the part being tested is immersed in the penetrant. The penetrant seeps into the defects on the surface. The part is then immersed in a solvent tank to remove the excess penetrant, and a developer is applied. Defects become visible as the developer absorbs the penetrant in contact with the defects.

3. Brushing Method: In this method, the penetrant is applied to the surface of the part being tested using a brush or spraying device. The penetrant seeps into the defects and is left for a specified period. Then, the excess penetrant is removed from the surface and a developer is applied. Defects become visible as the developer absorbs the penetrant in contact with the defects.

4. Capillary Method: In this method, the penetrant is applied to the surface of the part, and the penetrant naturally seeps into the capillary gaps in the defective areas. The excess penetrant is then removed from the surface and a developer is applied. Defects become visible as the developer absorbs the penetrant in contact with the defects.

These techniques are commonly used methods for detecting defects during penetrant testing. Each technique is selected and applied based on specific application requirements and part characteristics.

4. UT- Ultrasonic Testing

Ultrasonic testing is a non-destructive testing method that uses high-frequency sound waves to detect defects within materials. Here are the commonly used techniques for ultrasonic testing:

1. Pulse-Echo Technique: In this method, an ultrasonic transmitter (transducer) sends sound waves into the material. As the waves travel within the material, they reflect off defects or interfaces within the material. These reflections are received by the transducer and displayed on a screen. This method is commonly used for measuring material thickness and detecting subsurface defects.

2. Through-Transmission Technique: In this technique, ultrasonic waves are sent from one side and received by a receiver on the other side. The attenuation or change in the waves passing through the material is used to assess the quality and homogeneity of the material.

3. Phased Array Technique: In this method, a series of transducers send sound waves into the material in a controlled manner. This allows the waves to propagate at different angles, enabling the visualization of defects from various angles. This technique is used in parts with complex geometries and for detecting multiple defects.

4. Time-of-Flight Diffraction (TOFD) Technique: In this method, as sound waves travel within the material, they diffract from defects as well as interfaces within the material. These diffraction signals are used to detect and size the defects.

5. Shear Wave Technique: In this method, shear waves are used to detect defects within the material. Shear waves are used to detect deeper defects and are typically employed in challenging environments such as high temperature or high thickness.

These techniques are commonly used methods for detecting defects and assessing material quality during ultrasonic testing. Each technique is selected and applied based on specific application requirements and part characteristics.

5. RT- Radiographic Testing

Radiographic testing is a non-destructive testing method that uses X-rays or gamma rays to detect defects within materials. Here are the commonly used techniques for radiographic testing:

1. Film Radiography (Conventional Radiography): In this technique, the part being tested is exposed to an X-ray or gamma-ray source. The portion of the rays that pass through the part is captured on a film or digital detector. Defects or density changes are displayed on the film. Film radiography is commonly used to detect internal defects in dense materials such as metal and concrete.

2. Digital Radiography: In this method, the part being tested is exposed to an X-ray or gamma-ray source, and the rays are captured by a digital detector or imaging sensor. The sensor measures the density of the rays passing through and transmits this information to a computer. Defects or density changes are analyzed using digital imaging software.

3. Computed Radiography (CR): In this technique, the part being tested is exposed to an X-ray or gamma-ray source, and then placed on a phosphor plate or a radiographic plate used instead of film. The plate measures the density of the rays passing through. The plate is then scanned using a scanning device and a digital image is created by a computer. This image is used to identify and analyze defects.

4. Digital Radioscopy: In this method, moving or complex parts are scanned using X-rays or gamma rays. The images are then viewed and analyzed in real-time on a computer screen. This technique is widely used in processes such as welding quality control.

These techniques are commonly used methods for detecting defects and assessing material quality during radiographic testing. Each technique is selected and applied based on specific application requirements and part characteristics.

6. Eddy Current Testing - Electromagnetic Methods

Eddy current testing is a non-destructive testing method used to detect defects on metal surfaces using the principle of electrical current induction. Here are the commonly used techniques for eddy current testing:

1. Standard Probe Technique: In this technique, a probe is applied to the metal surface and a high-frequency alternating current is applied through the probe. Changes in electrical conductivity or magnetic properties on the metal surface generate a signal indicating the presence of defects.

2. Array Probe Technique: In this method, an array of probes is placed on the surface of the part. Each probe operates in a different area, allowing for a broad area scan. Array probe techniques provide faster scanning and wider coverage.

3. Rotary Probe Technique: In this technique, a rotary probe is used, which rotates close to the surface of the part. The rotating probe scans a wide area of the part's surface to detect defects. This technique is suitable for inspecting cylindrical or circular parts.

4. Remote Field Technique: This method allows the probe to operate a few millimeters away from the surface without contact. This way, defects just below the surface can be detected. This technique is used to detect defects under surface coatings.

5. Pulsed Eddy Current Technique: This technique uses pulsed eddy current signals. Pulsed signals can penetrate deeper into the part and are used to detect deeper defects.

These techniques are commonly used methods for detecting defects and assessing material quality during eddy current testing. Each technique is selected and applied based on specific application requirements and part characteristics.

7. ET- Eddy Current Testing

Eddy current testing (ET) is a non-destructive testing method used to detect defects in conductive materials based on electromagnetic induction principles. Here are the commonly used techniques for eddy current testing:

1. Standard Probe Technique: In this method, a probe is applied to the conductive surface and a high-frequency alternating current is applied through the probe. Changes in electrical conductivity or magnetic properties on the surface generate a signal indicating the presence of defects.

5. Pulsed Eddy Current Technique: This technique uses pulsed eddy current signals. Pulsed signals can penetrate deeper into the part and are used to detect deeper defects.

8. LT- Leak Testing

Leak testing is a non-destructive testing method used to detect leaks and determine leakage rates in various systems, components, and structures. Here are the commonly used techniques for leak testing:

1. Pressure Decay Method: This method involves pressurizing a closed system and measuring the pressure over time. Leaks are detected by the decrease in pressure. This method is often used to detect small leaks in gas or liquid systems.

2. Vacuum Decay Method: This method involves creating a vacuum in a closed system and measuring the pressure over time. Leaks are detected by the increase in pressure. This method is often used to detect small leaks in gas or liquid systems.

3. Bubble Emission Testing: This method involves submerging the system in a liquid and visually inspecting for bubbles forming at leak sites. This method is often used to detect leaks in air or gas systems.

4. Tracer Gas Testing: This method involves filling the system with a tracer gas, such as helium or hydrogen, and using specialized detectors to identify leaks. This method is highly sensitive and can detect very small leaks.

5. Mass Spectrometry Leak Detection: This method involves using a mass spectrometer to detect and measure the presence of tracer gases. This method is highly sensitive and is used to detect very small leaks.

These techniques are commonly used methods for detecting leaks and assessing leakage rates during leak testing. Each technique is selected and applied based on specific application requirements and part characteristics.