Liquid Penetration Test

July 22, 2017 | Author: Yuvaraj Maganathan | Category: Nondestructive Testing, Mechanical Engineering, Materials, Building Engineering, Chemistry
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At the end of this experiment, we were able to learn the methods of Liquid Penetration Test and able to detect the defect of the material such as scratch and crack. 2.0


Metal Specimen

Cleaner Liquid Spray

Penetration Liquid Spray

Developer Liquid Spray


SAFETY AND HEALTH 3.1 Make sure the students follows the laboratory or workshop safety regulators. 3.2 Experiment must be conducted by lectures or experienced lab assistance. 3.3 Always know the hazards associated with the materials that are being utilized in the lab. 3.4 Always wear appropriate protective clothing. 3.5 Never perform unauthorized work, preparations or experiments. 3.6 Be familiar with the location of emergency equipment – fire alarm, fire extinguisher, emergency eye washer, and safety shower. Know the appropriate emergency response procedures. 3.7 Safety precaution when using liquid spray, do not inhale the fume that came out from the liquid sprayer and make sure that your skin is not in contact with any liquid from this test. It might be corrosive.


THEORY Non-destructive testing (NDT) is the process of inspecting, testing, or

evaluating materials, components or assemblies for discontinuities, or difference 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. In contrast to NDT, other tests are destructing in nature and are therefore done on a limited number of samples, rather than on materials, components or assemblies actually being put into service. These destructive tests are often used to determine the physical properties of materials such as impact resistance, ductility, yield and ultimate tensile strength, fracture toughness and fatigue strength but discontinuities and difference in materials characteristics are more effectively found by NDT.

Today modern non-destructive tests are used in manufacturing, fabrication and inspections to ensure product integrity and reliability, to control manufacturing processes, lower production costs and to maintain a uniform quality level. During construction, NDT is used to ensure the quality of materials and joining processes during the fabrication and erection phases, and

in-service NDT inspections are used to ensure their usefulness and the

safety of the public. HISTORY OF LIQUID PENETRATION TEST The exact origin of liquid penetrant inspection is not known, but it has been assumed that the method evolved from the observation that the rust on a crack in a steel plate in outdoor storage was somewhat heavier than the rust on the adjacent surfaces as a result of water seeping into the crack and forcing out the oxide it had helped to produce. The obvious conclusion was that a liquid purposely introduced into surface cracks and then brought out again would reveal the locations of those cracks. The only material that fulfilled the known criteria of low viscosity, good wettability, and ready availability was kerosene. It was found, however, that although wider cracks showed up easily, finer ones were sometimes missed because of the difficulty of detecting, by purely visual means, the small amounts of kerosene exuding from them. The solution was to provide a contrasting surface that would reveal smaller seepages. The properties and availability of whitewash made it the logical choice. This method, known as the kerosene-and-whiting test, was the standard for many years. The sensitivity of the kerosene-and-whiting test could be increased by hitting the object being tested with a hammer during testing. The resulting vibration brought more of the kerosene out of the cracks and onto the whitewash. Although this test was not as sensitive as those derived from it, it was quick, inexpensive, and reasonably accurate. Thus, it provided a vast improvement over ordinary visual examination. The first step leading to the methods now available was the development of the fluorescent penetrant process by R.C. Switzer. This liquid, used jointly with a powder developer, brought penetrant inspection from a relatively crude procedure to a more scientific operation. With fluorescent penetrant, minute flaws could be readily detected when exposed to ultraviolet light (commonly called black light). This development represented a major breakthrough in the detection of surface flaws.

Switzer's work also included the development of the visible-color contrast method, which allowed for inspection under white light conditions. Although not as sensitive as fluorescent penetrant inspection, it is widely used in industry for noncritical inspection. Through the developments described above, liquid penetrant inspection has become a major nondestructive inspection method.




First of all the metal specimen is rubbed cleanly using steel brush.


The surface of the specimen is cleaned using the cleaner liquid. Besides that see the defects that occurred on the surface . The specimen is let to dried.


The penetration liquid is sprayed at the same surface. Then the specimen is let to dry for about 2-10 minutes.


The cleaner liquid is sprayed for the second time to clean excess penetration liquid on the specimen surface and let it dried using a hair dryer.


After that, the developer liquid is sprayed on the specimen and the surface is let to dry. The defects can be seen on the surface of the specimen.



i ii



Deep hole defect







Like all nondestructive inspection methods, liquid penetrant inspection has both advantages and disadvantages. The primary advantages and disadvantages when compared to other NDE methods are summarized below. Advantages  

The method has high sensitivity to small surface discontinuities. The method has few material limitations, i.e. metallic and nonmetallic, magnetic and

nonmagnetic, and conductive and nonconductive materials may be inspected. Large areas and large volumes of parts/materials can be inspected rapidly and at low

 

cost. Parts with complex geometric shapes are routinely inspected. Indications are produced directly on the surface of the part and constitute a visual

 

representation of the flaw. Aerosol spray cans make penetrant materials very portable. Penetrant materials and associated equipment are relatively inexpensive.

Disadvantages    

Only surface breaking defects can be detected.Only materials with a relatively nonporous surface can be inspected. Pre cleaning is critical since contaminants can mask defects. Metal smearing from machining, grinding, and grit or vapor blasting must be removed

    

prior to LPI. The inspector must have direct access to the surface being inspected. Surface finish and roughness can affect inspection sensitivity. Multiple process operations must be performed and controlled. Post cleaning of acceptable parts or materials is required. Chemical handling and proper disposal is required.

APPLICATION OF LIQUID PENETRATION TEST Materials that are commonly inspected using LPI include the following: 

Metals (aluminium, copper, steel, titanium, etc.)


Many ceramic materials



LPI offers flexibility in performing inspections because it can be applied in a large variety of applications ranging from automotive spark plugs to critical aircraft components. Penetrant materials can be applied with a spray can or a cotton swab to inspect for flaws known to occur in a specific area or it can be applied by dipping or spraying to quickly inspect large areas. In the image above, visible dye penetrant is being locally applied to a highly loaded connecting point to check for fatigue cracking. Penetrant inspection systems have been developed to inspect some very large components. In the image shown right, DC-10 banjo fittings are being moved into a penetrant inspection system at what used to be the Douglas Aircraft Company's Long Beach, California facility. These large machined aluminium forgings are used to support the number two engine in the tail of a DC-10 aircraft. Liquid penetrant inspection can only be used to inspect for flaws that break the surface of the sample. Some of these flaws are listed below:


Fatigue cracks

Quench cracks

Grinding cracks

Overload and impact fractures




Pin holes in welds


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