Non-Destructive Testing Handouts PDF

# NON-DESTRUCTIVE TESTING Non-destructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or...

# NON-DESTRUCTIVE TESTING Non-destructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or test is completed the part can still be used. The most important types of NDT are the following: - Magnetic Particle Testing (MPT) - Ultrasonic Testing (UT) - Radiographic Testing (RT) - Penetrant Testing (PT) ## 1. MAGNETIC PARTICLE TESTING Magnetic particle testing is a non-destructive testing method. Similar to other NDT methods, MPT or MPI is used to detect surface cracks or flaws in ferromagnetic easily magnetized materials, such as steel, nickel, cobalt, iron and their alloys. Magnetic particle testing makes use of tiny magnetic particles and magnetic fields to reveal flaws or discontinuities in various products, components or parts, such as castings, weldments and forgings. The primary objective of the process is to determine whether the components being tested are fit for use. ### Magnetic Particle Testing Diagram: A diagram of magnetic field lines and magnetic particles in the form of a rectangle, two arrows point to the right at the top and two arrows point to the left at the bottom of the rectangle. The word "AME" is at the bottom right corner of the diagram. ### Magnetic Particle Testing Types and Methods - The magnetic particles used in MPT can be used in the form of a dry mix or a wet solution. - The two types of magnetic particle testing methods are named after the type of magnetic particles used: wet magnetic particle testing (WMPT) and dry magnetic particle testing (DMPT). - The magnetic particle testing steps or procedure depends on whether dry or wet magnetic particles are used. ### Dry Magnetic Particles Dry magnetic particles are a mixture of fine and coarse particles ranging from 50 µm to 150 µm. They come in different colors like yellow, red, black, and others. Dry MPT is recommended for testing rough surfaces. It is also capable of detecting shallow subsurface flaws. Below are the steps in performing a dry magnetic particle test/inspection: 1. **Surface Preparation**: The ultrasonic cleaning method is used to ensure the surface of the test component or specimen is clean and free from moisture, oil, or grease. 2. **Introduction of Magnetizing Force**: A magnetic field or flux is introduced by using permanent magnets, a coil, an electromagnetic yoke, or something similar. 3. **Application of Dry Magnetic Particles**: A thin layer of the ferromagnetic medium (crushed magnetic particles) is sprinkled on the specimen while it is still magnetized. 4. **Removal of Excess Particles**: While the magnetizing force is being applied, any excess powder should be removed by applying low-pressure dry air from a syringe, bulb, or a similar source. Note that the force of air should be controlled to ensure it doesn't blow off the particles that have adhered or are stuck to the magnetic flux leakage field. 5. **Termination of the Magnetising Force**: The magnetising force is terminated; however, the permanent magnets may be left in place if they are still being used. 6. **Inspection and Interpretation**: The magnetic particles cluster in the faulty section/s. Observations are recorded, interpreted and evaluated according to acceptance standards. ### Wet Magnetic Particles Wet particles come in fluorescent shades in the form of an oil or water suspension. They are also smaller (10 µm and below), which makes them more mobile and adherent. Wet MPT is recommended for detecting minute discontinuities on smooth surfaces. It is also ideal for testing larger areas, as the wet particles are easy to apply. To perform a wet magnetic particle inspection, follow these steps: 1. **Surface Preparation**: Follow the same procedure in step 1 of dry MPT. 2. **Application of Wet Magnetic Particles**: Carefully spray on or pour the magnetic particle suspension on the component or specimen. 3. **Introduction of Magnetising Force**: Quickly apply the magnetising field after the suspended magnetic particles are poured or sprayed on the specimen. 4. **Inspection and Interpretation**: Just like in dry MPT, the magnetic particles will cluster in the faulty area. While there is a sharp indication of surface discontinuities, subsurface flaws tend to be less defined. Infrared lights are sometimes used to get a better vision of the faults on the surface of the specimen. Observations are then recorded, interpreted, and evaluated according to acceptance standards. ### Advantages - Defects can be detected directly on the surface - Easier to apply compared with other NDT methods - Fast and reliable - Flexible application, as there is a specific MPT method for either rough or smooth surfaces - Indicates the shape and size of the cracks - Makes use of portable and low-cost equipment - Relatively safe to perform - Results are immediate - Very sensitive, so it can detect even the finest surface flaws ### Disadvantages: - Application is limited to ferromagnetic materials like steels, cast irons, etc. - Post cleaning and demagnetization are usually required. - Recommended for inspecting small sections only specialized equipment may be required to examine large parts. - Testing should be done in two perpendicular directions. - Thick paints have to be removed prior to inspection. ### Applications of Magnetic Particle Testing There are several industry applications of magnetic particle testing: - **Mining**: To monitor equipment for damage and flaws, preventing failures, injuries, potential deaths and lost productivity. Often MPT is conducted on drill rigs, excavators, tyre handlers, lift or pad eyes and crane hooks. - **Aerospace**: To inspect the integrity of aircraft propeller hubs and turbine blades. - **Engineering and Fabrication**: To inspect electroslag (ES) welds on network-critical structures. - **Marine**: To check lift or pad eyes that have been welded onto a module. - **Oil and Gas**: To investigate the internal blistering of oil pipelines. - **Power Generation**: To inspect gas turbine blades. ### There are various types of NDT magnetic particle testing equipment available. These include: - Adjacent cables - Current flow probes - Demagnetisation equipment - Electromagnetic yokes - Flexible coils - Magnetic particle test blocks - Permanent magnets - Power packs - Threading bars - Wet benches ## 2. ULTRASONIC TESTING Ultrasonic testing is a type of non-destructive testing method that works by sending ultrasonic waves through the object or material being inspected. - During ultrasonic testing, the inspector uses a probe or a certain other kind of transducer to transmit sound waves that penetrate the material they want to test. If the material is flawless or has no defects, the sound waves will simply pass through it. However, if the sound waves hit a flaw or defect, they will bounce off and rebound, thereby indicating the presence of a flaw in the material. - The signal from the sound waves can be used by inspectors to create a 3-dimensional visualization of the material. Doing so makes determining the distances between various defects found in the material easier. - A common application for the UT method is for ultrasonic thickness measurement. It is used to determine the thickness of an object, as in the case of Pressure Vessel and pipework corrosion assessment. ### Ultrasonic Testing Methods: 1. **Pulse-Echo Testing Method** - The ultrasound pulse echo testing method is more sensitive than through-transmission. It is used to identify flaws in a material by measuring the amount of time it takes for amplitude signals to travel between different points or surfaces in the material being tested. A diagram of a transducer showing the probe hitting the material and then bouncing back to the probe, which is displayed. 2. **Through-Transmission Method** - The through-transmission method uses two transducers, with each one placed on opposite sides of the material being inspected. One transducer creates a pulse while the other receives it. When a disruption in the pulse is detected, inspectors will know that a flaw or defect is present in the route between the two transducers. A side view diagram of the test being completed shows a transducer on each side of the object and the pulse being transmitted through the object. ### Ultrasonic Testing Types: 1. **Contact Ultrasonic Testing** - Typically used for on-site inspections accessibility or portability. Contact ultrasonic inspection can be performed where only one side of a test specimen is reachable, or where the parts to be tested are large, irregular in shape or difficult to transport. 2. **Ultrasonic Immersion Testing** - Ultrasonic immersion testing involves the inspection of engineering parts and components submerged in water by ultrasound. Here, the test object is placed in a tank filled with water and an ultrasound probe is moved over the surface of the part being checked. ### Applications of Ultrasonic Testing: Ultrasonic testing has a range of applications across different sectors, including the mining, aerospace, automotive, construction, rail, medical and oil and gas industries. It is particularly useful in testing the integrity of certain materials or components. This includes: - Ultrasonic pipe thickness testing; - Short range ultrasonic testing for storage tanks; - Conveyor belt thickness - Tailings pipe (PE Pipe) thickness - Defect sizing ultrasonic testing for aerospace components and structures; - UT can also be utilized to detect finer defects and planar flaws which may not be detected easily with radiographic testing. ### UT Thickness Testing Ultrasonic thickness testing (UTT) or gauging is done to determine the extent of corrosion and erosion in storage tanks, piping walls, pressure vessels and other equipment. It measures the thickness of the material being checked through the use of the contact pulse-echo technique at temperatures not exceeding 93°C (200°F). ### Advantages - Excellent penetration power which enables UT to detect flaws or imperfections located deep with a component, part or asset - High level of sensitivity that allows for the accurate detection of even the smallest flaws. - Capable of being utilized for testing an object even if only one side is accessible. - Greater precision in detecting the depth of internal flaws and the thickness of parts with parallel surfaces when compared with other NDT methods. - Ability to estimate the size, shape, orientation and nature of the defects with a high degree of accuracy. - Can estimate the alloy structures of parts or components with varying acoustic properties. - Safe or non-hazardous to nearby personnel, equipment or materials. - Automated and portable operations in different job sites possible. ### Disadvantages - Objects or parts that are rough, irregularly shaped, very small or thin, or not homogeneous are challenging to inspect. - Conventional UT requires the use of couplants for testing. - UT sensitivity may be reduced in relation to volumetric flaws, especially with metal inclusions. There are various types of ultrasonic NDT equipment used to carry out ultrasonic testing, including: - Power supply - Transducer - Pulser/receiver - Sweep generator - Display and timer ## 3. PENETRANT TESTING - Penetrant testing is also called liquid penetrant testing (LPT), dye penetrant testing or inspection (DPT or DPI). The key term here is 'penetrant' as the test or inspection done is so labelled based on the type of penetrant specialized liquid used – whether it's dye usually red in color or a fluorescent material. - PT is an NDT technique extensively used in inspecting various components used in the mining industry, such as ball and rod mills, conveyances, crushers, furnaces, hoists, process piping, pressure vessels and tanks. Below are the general liquid penetrant testing steps: - Clean the surface of the test material - Apply the liquid penetrant - Remove the excess penetrant - Apply the developer - Inspect the test material - Clean the test material ### Applications of Penetrant Testing: - Any solid, non-porous items, such as metals, ceramics, organic and composite materials, can be tested through liquid penetrant testing. PT is often used to detect discontinuities in materials and to find defects in castings, forgings, and welded parts, such as during corrosion tests. - Penetrant testing or inspection is extensively used to evaluate and detect surface discontinuities on components used in a range of industries, including energy or power generation, mining, aviation, aerospace engineering, manufacturing, military, petrochemicals, and construction. ### Advantages: - It can be used on a wide range of non-porous materials, including metallic and non-metallic, magnetic and non-magnetic, and conductive and non-conductive materials. - It allows for the convenient and rapid inspection of large volumes of materials. - It can be used even on parts with irregular or complex shapes. - It enables the inspector to observe indications directly on the surface of the part being tested. - The materials and equipment needed to conduct PT are low cost. ### Disadvantages: - It can only be used for detecting surface-breaking defects. - Its application is limited to non-porous materials or surfaces. - The pre-cleaning step is highly critical as improper cleaning can leave contaminants that can mask material defects. - Pre- and post-cleaning of test parts or materials is necessary. To conduct penetrant testing, you will need the following materials: - Test surface or material - Cleaner (solvent remover, detergent, vapour degreaser, etc.) - Penetrant (red for non-fluorescent dye penetrant testing or fluorescent) - Cleaner or water to be used for removing any excess penetrant - Developer - Several clean, lint-free rags or cloths - White (for non-fluorescent dye penetrant testing) or UV (for fluorescent dye penetrant testing) light - PPE or gloves for protection ## 4. RADIOGRAPHIC TESTING - Radiographic Testing or Radiographic Examination is a non-destructive testing (NDT) method for examining the internal structure of any component to identify its integrity. Radiographic Testing or RT uses x-rays and gamma-rays to produce a radiograph of the test specimen that shows changes in thickness, defects or flaws, and assembly details to ensure optimum quality. - Radiographic testing of welds to ensure weld quality is a widely used industry practice. Radiographic testing in welding is a highly dependable way to detect weld defects like cracks, porosity, inclusions, voids, lack of fusion, etc. in weld interiors. Because of its high dependability, radiographic testing is widely used in the oil & gas, aerospace, transport, military, automotive, manufacturing, offshore, petrochemical, marine, and power generation industries. ### Radiographic Testing Procedure: Surface Preparation: Surface irregularities must be removed so that they can not mask or confuse the image as a defect. - Selecting the right radiation source and radiographic film: Depending on radiographic sensitivity and material thickness radiation source (x-ray or gamma-ray) must be decided. - Selection of Penetrameter: As per SE 142 or SE 1025 (for whole type) and SE-747 (for wire type), ASME V & ASME Sec VIII Div I, whole type or wire type penetrameter need to be selected. - Radiographic testing technique: Single or Double wall exposure technique is used. Source-to-object and object-to-source distances must be established beforehand. - Defect inspection and removal: The radiograph is to be studied for probable defects and repaired if the defect is observed. - Recording: All data need to be properly recorded. ### Codes and Standards for Radiographic Testing Widely used codes and standards for radiographic testing are: - ISO 5579, Non-destructive testing – Radiographic examination of metallic materials by X- and gamma-rays – Basic rules - ASME SE: Standard Method for Controlling Quality of Radiographic testing. - ASME SE 94: Recommended Practice for Radiographic Testing - ASTM E 801, Standard Practice for Controlling Quality of Radiological Examination of Electronic Devices - API 1104, Welding of Pipelines and Related Facilities: 11.1 Radiographic Test Methods - AASME SE V: Boiler and Pressure Vessel – Non-Destructive Testing. - ASTM 1161, Standard Practice for Radiologic Examination of Semiconductors and Electronic Components - ISO 10675-1, Non-destructive testing of welds Acceptance levels for radiographic testing – Part 1: Steel, nickel, titanium and their alloys - SNT-TC-1A: Recommended Practice for Personnel Qualification and Certification in Non-destructive Testing. - ASTM E 592, Standard Guide to Obtainable ASTM Equivalent Penetrameter Sensitivity for Radiography of Steel Plates - ASTM E 1030, Standard Test Method for Radiographic Examination of Metallic Castings - ASTM E 1815, Standard Test Method for Classification of Film Systems for Industrial Radiography - EN 12681, Founding – Radiographic examination - ASTM E 1032, Standard Test Method for Radiographic Examination of Weldments - ISO 4993, Steel and iron castings – Radiographic inspection ### Advantages - Assembled components can easily be inspected. - The surface preparation requirement is minimal. - Both surface and subsurface flaws can be detected. - Easily verify internal defects on complex items/structures - Automatically detect and measure internal flaws - Dimensions and angles of the sample can be measured without sectioning. ### Disadvantages: - Highly hazardous, so proper care must be exercised. - The high degree of skills and experience required. - Costly affair. - Slow process. - Two-sided access to components is required. ### Radiographic Testing Equipment: - X-ray Generators or Gamma Ray Sources - Detectors - Radiographic Film or Digital Imaging Systems - X-ray Control Panels - Collimators - Lead Screens and Intensifying Screens - Radiation Safety Equipment