How to Select Nondestructive Testing (NDT) Supplies
Image Credit: SENTINELTM
NDT supplies and accessories are components, ancillary equipment, standards, and consumable materials used in non-destructive testing (NDT). Nondestructive testing is a method used to provide material composition analysis without compromising or altering the physical structure of a material.
NDT supplies include a diverse range of products that can be classified based on the type of testing they involve. Selecting the right NDT supplies or accessories depends mostly on the type of NDT required. This selection guide is designed to help buyers understand these different testing types and the supplies that are used for them.
Dye Penetrant Testing
Dye penetrant testing is a low cost method to detect flaws or defects in a non-permeable membrane. Colored indicator dye is applied onto the surface of a membrane, and is watched for movement. If the dye travels into or through a membrane at a certain point, the defective area can then be properly repaired or replaced. A specific type of dye testing known as fluorescent penetrant inspection (FPI) uses fluorescent dye to test membrane integrity.
Figure 1 -An illustration and description of the dye penetration test process. Graph Credit: Magnetic Inspection Laboratory, Inc.TM
Dye penetrant testing can be done on virtually any material and the results appear directly on the surface of the material. Supplies for dye penetrant testing include a range of products from dye cleaners to emulsifiers.
- Penetrant removers or cleaners are designed for the pre-cleaning and post cleaning stages of penetrant inspection process.In the pre-cleaning stage,a cleaner, degreaser,orsolventis used to remove surface contamination such as cutting oils, greases, shop dust, swarf,or soot. In the post cleaning stage,a cleaneror removeris usedremove residual penetrant fromthe surface of apart so theliquid penetrant only remains in the surface flaws or cracks that are present.
- Contrast paint or aerosol products can provide greater contrast between the dye penetrant or powder and the background to improve visual detection.
- Developers improve flaw visibilityby pulling the penetrant retainedin a cavity orcrack to the surface. Developers are available in dry powder and aqueous forms depending on the specific penetrant testing method. In thedry powder method, powdersare blown onto the part with a bulb, powder applicator, or swirl chamber after the application of penetrant to develop or enhance detection of the surface flaw. The fluorescent powder sticks to the penetrant remaining in a flaw or surface crack after cleaning. In the aqueous based developer methods, the powders are suspended in a liquid that is applied to the part by spraying or immersion.
- Emulsifiers are liquid additives used to emulsify or enhance the suspension of penetrants.
- Penetrant test kits or spot testers are small, portable penetrant testing kits for on-site evaluations in the field or plant or for testing large equipmentthat will not fit into the penetrant testing lab. The kit should contain required consumables,sprayers, and applicators.
- Penetrants or leak testers are applied to a part by spray or immersion and the penetrant is pulled intosurface flaws by capillary action.Next, a cleaneris usedto remove residual penetrant fromthe surface of apart so theliquid penetrant only remains in the surface flaws or cracks that are present.Penetrant systems are available in visible or fluorescent forms with varying sensitivity levels depending on the material and flaw type being inspected. Red dyepenetrants arevisible under normallight.Fluorescent penetrants or penetrant systems may require UV or blacklight illumination.Developers orpowders may be required to enhancevisibility ofthe residual penetrant entrapped in the crack. Penetrants are also used for leak detection through the bubble detection for pressurized vessels.
- Sprayers can be manual, pneumatic, pump-based, or electrostatic and are used to apply penetrant to components being tested.Sprayers are useful for large parts that cannot be immersed or for spot-checking of components in the field.
Magnetic Particle Inspection
Magnetic particle Inspection (MPI) is an NDT process for detecting surface and subsurface discontinuities in ferroelectric materials. When a material is magnetized, ferrous particles will be drawn to areas of missing metal or corrosion, where the magnetic field "leaks" out.
Figure 1 -An illustration of the MPI process, showing magnetization of both longitudinal fields and circular fields. Graph Credit: Magnetic Inspection Laboratory, Inc.TM
MPI is quick and easy to perform and the results are instantaneous. It is, however, limited to materials that have the ability to be magnetized. Supplies for MPI testing include a range of products from coil magnetizers to conductors.
- Coil magnetizers are used to magnetize a product for magnetic particle testing.The part is passed through or laid on top of the magnet.Magnetic poles created at flaws, cracks, or other discontinuities attract magnetic particles.
- Conductors are bars or rods placed inside atube, pipe, or hollow part; current is applied;andcircular magnetization of the part is provided. The conductors may also be used to pass magnetizing current to contact plates or clamps.
- Contact pads, blocks, plates, or clamps are used to conduct magnetizing current to parts. Contact pads usually consist of braided copper.Contact plates are often made of soft lead to provide low contact resistance.
- Demagnetizers are used to remove any permanent magnetism from parts after testing.A magnetized motor shaft could cause problems if used in a magnetized condition.
- Magnetic particles are fine iron oxide particles with a high permeability (easily magnetized) and low retentivity (ability to stay magnetized). Magnetic particles typically rangein size between 0.125 to60 microns.Three methods are typically applied: dry non-fluorescent, wet non-fluorescent,and wet fluorescent. Dry particles are chemically dyed gray, red, black and yellow to provide contrast against the background of the test surface. A powder applicatoris used such as a squeeze bulb or spray gun. Wet suspension particles are suspended in an oil based or water based liquid vehicle or carrier. In water-based suspensions,additional conditioners are required such aswetting agents and corrosion inhibitors.
- Magnets or magnetic rubber are used to enhance or alter magnetic fields or magnetization.
- Magnetizer power packs are stationary AC or DC power supplies forelectromagnet magnetizers.
- Yoke magnetizers arehorseshoe shaped electromagnets used to magnetize parts for magnetic particle testing. An intense magnetic field is created between the yoke legs. Magnetic poles created at flaws, cracks or other discontinuities attract magnetic particles.
Radiographic or X-ray Inspection
Radiographic and X-ray inspection is an NDT method that detects flaws in a material by penetration of high energy photons. The amount of unabsorbed radiation can then be measured to determine thickness or material composition.
Figure 3 - An illustration of the radiographic inspection process, showing an inspection and a photographic film quality check. Graph Credit: Magnetic Inspection Laboratory, Inc.TM
Radiographic testing has high sensitivity for most defect detection but consequently is a more costly inspection procedure than alternative NDT methods. There is also a radiation hazard when using this method, and some cracks oriented normal to the radiation source run the risk of not being detected. Supplies for radiographic or x-ray inspection include a range of products from darkroom equipment to penetrameters.
- Darkrooms are mobile or fixed rooms for development of exposed radiographic film images.
- Darkroom equipment includes items such as film drying cabinets, hangers, processors, spirals, or viewers as well as darkroom trays, rinsing stations, bottles, and dispensers for solutions.
- Dosimeters or survey meters are instruments for monitoring or measuring radiation such as dosimeters, survey meters, or other radiation monitors.
- Film chemicals are substances required for developing or processing exposed film.
- Imagers or cameras are devices for electroniccapture of radiographic images.Solid-state detectors, imagers or CCD cameras are also available that will capture electronic images.
- Imaging plates or fluoroscopic screens are devices for temporarycapture of radiographic images.The device may be used to expose conventional film. Fluorescent screens convert x-rays or other radiation into visible light using phosphorescent coating on a glass plate or plastic film. Imaging plates capture image data in aphoto-stimulable phosphorlayer coatedon a plastic sheet.The captured imageis later converted into an electronic format by scanning with a laser and photo-multiplier tube.The laser stimulates the release of light that is detected bythe photo-multiplier tube.
- Penetrameters are used to measure the penetrating power or kilovoltage of x-rays or gamma rays in conjunction with x-ray imaging or radiography. Penetrameters are also usedmeasure the penetrability ofa sample.
- Photographic films are used for capturing x-ray or radiographic images.
- Shielding or enclosures are accessory components used during a test to avoid exposingpersonnel and equipment to radiation. The componentcontains the inspected partand the penetrating x-rays during a test.Shields or enclosuresare constructed of metals or materials that absorb x-rays. Interlocksprovide a safety lock that prevents a power on condition while an enclosure is open.
- X-ray opaque markers are lead markers, barium putty, or lead letters used to mark or label radiographic images.
General Supplies and Accessories
General supplies and accessories include a long list of products that can be used independently or in various NDT applications. For a detailed description of the different types of general supplies and accessories, please visit the "General Supplies & Accessories" section of the Search by Specification page for NDT Supplies and Accessories.
- Cable / Adapter
- Cleaner / Penetrant Remover
- Coil Magnetizer
- Contact Pad / Plate / Clamp
- Contrast Paint / Aerosol
- Darkroom / Processing Equipment
- Dosimeter / Survey Meter
- Film Cassette
- Film Chemicals / Developer
- Film Viewer
- Flaw Standard / Test Panel
- Holder / Clamp
- Imagers / Cameras
- Imaging Plate / Fluoroscopic Screen
- Light Meter
- Magnetic Particles
- Magnetizer Power Pack
- Magnifier / Mirror
- FPI / Dye Penetrant Testing:Other
- Magnetic Particle Inspection:Other
- Radiographic / X-ray Inspection:Other
- General Supplies & Accessories:Other
- Particle Filtration / Chemical Recovery System
- Penetrant / Leak Tester
- Penetrant Test Kit / Spot Tester
- Photographic Film
- Powder Dispenser
- Radiographic Film Standard
- Scanner / Pipeline Crawler
- Shielding / Interlock / Enclosure
- Thickness Calibration Block
- UV Lamp / Blacklight
- Ultrasonic Couplant
- X-ray Opaque Marker / Tape
- Yoke Magnetizer