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Nondestructive Testing (NDT)

Nondestructive Testing (NDT) is a quality control inspection that does not damage or destroy the materials or objects being tested. It’s the most reliable way to test equipment for defects from fatigue, structural flaws, and other problems that could lead to serious injury and or the costly shutdown of your facility.

Hoosier Crane performs two of the main types of nondestructive testing, magnetic particle testing and liquid penetrant testing. Both are much more precise than basic observation inspections.

Our service technicians are certified and experienced in these testing methods. They are prepared to give your equipment the most accurate and reliable evaluations possible.

Liquid Penetrant Testing
Magnetic Particle Testing
Liquid Penetrant Testing

Liquid Penetrant Testing

Testing for Surface Defects

Liquid penetrant testing, also known as dye penetrant or dye pen testing, is a cost effective way to test for defects open to the surface. It is an effective nondestructive means of testing a variety of materials such as aluminum, magnesium, brass, copper, cast iron, steel, stainless steel, carbides, stellite, certain plastics, and ceramics.

When getting started with a liquid penetrant test it is absolutely critical that the surface is prepared properly. The surface must be free of oil, grease, water, or other contaminants that may prevent the penetrant from entering and exposing cracks and flaws. Then, once the surface is thoroughly cleaned and dried, the liquid penetrant is applied. Typically, the penetrant is sprayed on or brushed on, but sometimes the object being tested is immersed in a penetrant bath. After the penetrant is applied it must be left on the surface area for a sufficient amount of time, allowing it to be drawn from or seep into a defect. The time required varies on the penetrant and the recommendations of the producers. The so called dwell times can range anywhere from five to 60 minutes. In general, there is no harm in using a longer dwell time as long as the penetrant is not allowed to dry. Once the liquid has been applied and given the time to locate flaws the excess penetrant must be removed. This is perhaps the most delicate part of the inspection procedure because the excess liquid must be removed from the surface of the sample while removing as little penetrant as possible from defects. Depending on the penetrant system used, this step may involve cleaning with a solvent, direct rinsing with water, or first treating the part with an emulsifier and then rinsing with water. Once this is carefully done, a thin layer of developer is applied to draw out the penetrant trapped in flaws back to the surface where it will be visible. Developers come in a variety of forms that may be applied by dusting (dry powdered), dipping, or spraying (wet developers). Again, timing is important. The developer must be given enough time to expose the cracks and flaws into which the penetrant has seeped. In general it takes about ten minutes. The actual inspection process must be performed under the appropriate lighting to detect indications of any flaws. This must be done very carefully.

This type of testing has its advantages and disadvantages. On the positive side it allows the inspector to find very fine flaws and it's great for smaller objects that have unusual shapes. It can be done on both magnetic and non-magnetic metals, as well as conductive and nonconductive materials. It's a relatively simple process and it's inexpensive. On the other side of the coin, it can be time consuming and a little messy. Only materials with relatively nonporous surfaces can be inspected and only surface breaking defects can be detected. The surface finish and roughness of the item being tested can also impact inspection sensitivity. On the whole though, it is considered a reliable test that can really help businesses find problems before they become big and expensive issues. Please contact Hoosier Crane for more information.

Magnetic Particle Testing

Magnetic Particle Testing

Magnetic Particle Testing is the other type of nondestructive testing that we do at Hoosier Crane. It's considered a low-cost method of testing ferromagnetic material. Ferromagnetic describes materials that can be magnetized or strongly attracted by a magnetic field. This type of test checks for surface discontinuities but can also reveal discontinuities slightly below the surface. There are different methods for this type of testing but the yoke technique is the most common method. It is what we typically do at Hoosier Crane. A yoke is a device with an electric coil in it that creates a magnetic field which can be transferred from the legs of the yoke to the part that will be examined. Most yokes can operate in alternating current (AC) or direct current (DC) modes. DC gives the most penetration and is recommended if subsurface discontinuities need to be detected. AC is recommended if the surface is rough, because AC gives the particles more mobility than DC.

The first step when doing a magnetic particle test is very similar to the first step of a liquid penetrant test. The surface of the item under inspection must be thoroughly cleaned. This can be done by using detergents, organic solvents, descaling solutions, paint removers, and other cleaning methods. Then, the inspector uses the yoke to introduce a magnetic field into the part. A ferromagnetic medium is then applied to that part while it is still magnetized. The next step is to remove any excess ferromagnetic medium to make it easier to interpret and evaluate the indications of potential problems. Much like the liquid penetrant, the ferromagnetic medium will expose flaws and potential problems in the item under inspection.

This type of nondestructive testing also has advantages and disadvantages. Like the liquid penetrant test it is also relatively easy to use and it's inexpensive. It can be used indoors, outdoors, inside vessels and tanks, and in all positions. This test can detect issues on the surface and slightly below the surface. It's a pretty fast method and the equipment is very portable. It's also much less messy than the liquid penetrant test. Perhaps the biggest disadvantage of this type of test is that it cannot be used on non-ferrous materials such as aluminum, magnesium, and stainless steel. If large parts are being inspected it may involve equipment with special power requirements. It may also require the removal of coating or plating to get the desired results.

NDT Certified Service Technicians

Hoosier Crane service technicians are all certified to perform both of these nondestructive testing methods. Both methods have advantages and disadvantages, depending on the parts that need to be tested. Please feel free to contact us if you have any questions about the best way to inspect your parts and to schedule a nondestructive test. These tests are much more accurate than standard visual tests, providing businesses with much more clarity about the safety of their equipment.