NONDESTRUCTIVE TESTING METHODS
Provided Services
LIQUID PENETRANT TESTING
Liquid penetrant testing is one of the most popular Nondestructive Testing (NDT) methods in the industry. It is economical, versatile, and has a quick turn-around time when compared to other NDT methods. Liquid penetrant checks for material flaws open to the surface by flowing very thin liquid into the flaw and then drawing the liquid out with a chalk-like developer. Welds are the most common item inspected, but plate, bars, pipes, castings, forgings, and many other components are also commonly inspected using liquid penetrant testing.
Over the years, liquid penetrant testing has been called many names: penetrant testing (PT), liquid penetrant testing (LP), and dye penetrant testing (DP). The American Society for Nondestructive Testing (ASNT) uses the name liquid penetrant testing (PT). The American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME B & PVC) and the National Board Inspection Code (NBIC) use the name liquid penetrant examination (PT).
There are many advantages to Liquid Penetrant testing such as: high sensitivity to small surface discontinuities, an easy inspection of parts with complex shapes, a quick and inexpensive inspection of large areas and large volumes of parts/materials, few material limitations (metallic and nonmetallic, magnetic and nonmagnetic, and conductive and nonconductive can all be inspected), a visual representation of the flaws are indicated directly on the part's surface, aerosol spray cans make the process portable, convenient, and inexpensive, and indications can reveal relative size, shape, and depth of the flaw. With every inspection type, Liquid Penetrant testing has its limitations. These limitations include: it detects flaws only open to the surface, materials with porous surfaces cannot be examined using this process, only clean, smooth surfaces can be inspected. (Rust, dirt, paint, oil and grease must be removed.), metal smearing from power wire brushing, shot blasting, or grit blasting must be removed prior to liquid penetrant examination, examiner must have direct access to surface being examined, and surface finish and roughness can affect examination sensitivity. (It may be necessary to grind surfaces before PT.) Even with a few limitations, Liquid Penetrant testing remains a reliable and the most widely used NDT method in the industry. Our nondestructive testing experts are highly capable of performing on-site or in-house liquid penetrant inspections at our NDT laboratory.
Contact our office to speak with our certified technicians for more information to best suit your needs.
MAGNETIC PARTICLE TESTING
Magnetic Particle Testing (MPT), also referred to as Magnetic Particle Inspection, is a Nondestructive Testing (NDT) method used to detect surface and slightly subsurface flaws in most ferromagnetic materials such as iron, nickel, and cobalt, and some of their alloys. Because it does not necessitate the degree of surface preparation required by other nondestructive test methods, conducting MPT is relatively fast and easy. This has made it one of the more commonly utilized NDT techniques.
MPT is a fairly simple process with two variations: Wet Magnetic Particle Testing (WMPT) and Dry Magnetic Particle Testing (DMPT). In either one, the process begins by running a magnetic current through the component. Any cracks or defects in the material will interrupt the flow of current and will cause magnetism to spread out from them. This will create a “flux leakage field” at the site of the damage. The second step involves spreading metal particles over the component. If there are any flaws on or near the surface, the flux leakage field will draw the particles to the damage site. This provides a visible indication of the approximate size and shape of the flaw.
There are several benefits of MPT compared to other NDT methods. It is highly portable, generally inexpensive, and does not need a stringent pre-cleaning operation. MPT is also one of the best options for detecting fine, shallow surface cracks. It is fast, easy, and will work through thin coatings. Finally, there are few limitations regarding the size/shape of test specimens. Despite its strengths, the method is not without its limits. The material must be ferromagnetic. Likewise, the orientation and strength of the magnetic field is critical. The method only detects surface and near-to-surface defects. Those further down require alternative methods. Large currents are sometimes required to perform this method, thus “burning” of test parts is sometimes possible. In addition, once MPT has been completed, the component must be demagnetized, which can sometimes be difficult. However, MPT's strengths heavily outweigh its limitations as it is still one of the more commonly used NDT methods. Garrow Inspection Services operates full-service nondestructive testing and magnetic particle inspection laboratories that utilize advanced equipment capable of performing quality inspections on-site and in-house.
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ULTRASONIC TESTING
Ultrasonic testing (UT) comprises a range of non-destructive testing (NDT) techniques that send ultrasonic waves through an object or material. These high frequency sound waves are transmitted into materials to characterise the material or for flaw detecting. As a non-destructive testing method, ultrasonic testing is ideal for detecting flaws and defects without damaging the object or material being tested. Periodic ultrasonic inspections can also be used to check for corrosion or for growth of known flaws, and thus potentially prevent to a failure of a part, component or entire asset. It is used in a wide range of industries including aerospace, automotive, construction, medical, metallurgy, and manufacturing.
Ultrasonic inspection uses a piezoelectrictransducer connected to a flaw detector, which in its most basic form is a pulser-receiver and oscilloscope display. The transducer is passed over the object being inspected, which is typically coupled to the test object by gel, oil or water. Ultrasonic testing can be performed using two basic methods – pulse-echo and through-transmission. With pulse echo testing, the same transducer emits and receives the sound wave energy. This method uses echo signals at an interface, such as the back of the object or an imperfection, to reflect the waves back to the probe. Results are shown as a line plot, with an amplitude on the y-axis representing the reflection’s intensity and distance or time on the x-axis, showing the depth of the signal through the material. Through-transmission testing uses an emitter to send the ultrasound waves from one surface and a separate receiver to receive the sound energy that has reached the opposite side of the object. Imperfections in the material reduce the amount of sound that is received, allowing the location of flaws to be detected.
Ultrasonic testing has many advantages such as: high penetration power, allowing for flaw detection deep within a part, high sensitivity, allowing for the detection of very small flaws, can be used to test when only one side of an object is accessible, greater accuracy when compared to other nondestructive testing methods, ability to determine depth of internal flaws and the thickness of parts with parallel surfaces, ability to estimate size, shape, orientation and nature of defects, ability to estimate alloy structures of components with differing acoustic properties, it’s non-hazardous to nearby personnel, the equipment or materials, highly automated and portable operation are possible, and immediate results can be obtained, allowing for immediate decisions to be made. UT has very few limitations yet some do still remain. These limitations are as follows: false positive results, also known as spurious signals, may result from tolerable anomalies as well as the component geometry itself, objects that are rough, irregularly shaped, very small or thin, or not homogeneous are difficult to inspect, and loose scale or paint will need to be removed before testing can commence, although clean, properly bonded paint can be left in place. Even with a few limitations, Ultrasonic testing is one of the most accurate and in-depth NDT techniques available. Our ultrasonic testing experts provide in-house, onsite and field inspections and certifications.
Contact our office to speak with our certified technicians for more information to best suit your needs.
EDDY CURRENT TESTING
Eddy Current testing is one of several non-destructive testing methods that uses the electromagnetism principle for flaw detection in conductive materials. A specially designed coil energized with an alternating-current is placed in proximity to the test surface, generating a changing magnetic field that interacts with the test-part and produces eddy currents in the vicinity. Variations in the changing phases and magnitude of these eddy currents are then monitored through the use of a receiver-coil or by measuring changes to the alternate current flowing in the primary excitation-coil. The electrical conductivity variations, the magnetic permeability of the test-part, or the presence of any discontinuities, will cause a change in the eddy current and a corresponding change in phases and amplitude of the measured current. The changes are shown on a screen and are interpreted to identify defects.
Eddy Current Testing has a wide variety of applications. These applications include, but are not limited to: Welded joints, Bores of in-service tubes, Bores of bolt holes, Metal tubes, Friction stir welds, Gas turbine blades, Nozzle welds in nuclear reactors, Hurricane propeller hubs, Cast iron bridges, Gas turbine blades, Aircraft, and Aircraft Parts and Components. Furthermore, Eddy Current is capable of detecting several types of defects such as: Surface-breaking defects, Linear defects (as small as 0.5mm deep and 5mm long), Cracks, Lack of fusion, and Generalized corrosion (particularly in the aircraft industry for the examination of aircraft skins). Additional capabilities of Eddy Current Testing are: Identification of both ferrous and non-ferrous metals and with certain alloys – in particular the aluminum alloys, establishing the heat treatment condition, determining whether a coating is non-conductive, and heat treat verification of metals.
Over the years, probe technology and data processing have advanced to the point where eddy current testing is recognized as being fast, simple, and accurate. Additional benefits of Eddy Current Testing include: detecting surface and near-surface cracks as small as 0.5mm, detecting defects through several layers, including non-conductive surface coatings, without interference from planar defects, non-contact method making it possible to inspect high-temperature surfaces and underwater surfaces, effective on test objects with physically complex geometries, provides immediate feedback, portable and light equipment, quick preparation time, and ability to measure electrical conductivity of test objects. Eddy Current Testing has very few restrictions compared to other nondestructive testing methods however, these limitations include: Can only be used on conductive materials, the depth of penetration is variable, susceptible to magnetic permeability changes – making testing of welds in ferromagnetic materials difficult – but with modern digital flaw detectors and probe design, not impossible, and it is unable to detect defects that are parallel to the test object’s surface. With very few restrictions Eddy Current Testing is one of the most effective and desirable nondestructive testing methods in the field. Garrow Inspection Services certified Eddy Current technicians are ready and capable of performing eddy current inspections on-site and in-house to meet the requirements of your job.
Contact our office to speak with our certified technicians for more information to best suit your needs.
RADIOGRAPHIC TESTING (X-RAY)
Radiographic Testing (RT) is a nondestructive testing (NDT) technique that involves the use of either x-rays or gamma rays to view the internal structure of a component. In the petrochemical industry, RT is often used to inspect machinery, such as pressure vessels and valves, to detect for flaws. RT is also used to inspect weld repairs. Radiography uses a sensitive film which reacts to the emitted radiation to capture an image of the part being tested. This image can then be examined for evidence of flaws in weld quality, castings, structures, and composites. It is used predominantly in the fabricating and casting industries for quality control, where it reveals faults such as porosity, inclusions, and cracks.
Compared to other NDT techniques, radiography has several advantages. It is highly reproducible, can be used on a variety of materials, and the data gathered can be stored for later analysis. Radiography is an effective tool that requires very little surface preparation. Moreover, many radiographic systems are portable, which allows for use in the field. The biggest limitation to this technique is that films can only be used once and the film has to be processed and interpreted. Whether you require on-site field services or in-lab RT laboratory analysis, our certified Technicians deliver the certainty your radiographic inspection projects require.
Contact our office to speak with our certified technicians for more information to best suit your needs.
