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Applications
Published in Cameron Coates, Valmiki Sooklal, Modern Applied Fracture Mechanics, 2022
Cameron Coates, Valmiki Sooklal
Liquid penetrant testing (PT) involves the application of a very low viscosity (highly fluid) liquid, known as the penetrant, to the surface of the part to be tested. Prior to the liquid application, the surface should be cleaned and free of oil, grease, water, or other contaminants. Once the fluid is applied it seeps into any defect such as cracks, fissures, and voids that are open on the material surface [19]. Sufficient time is needed for this step to allow as much penetrant as possible to be drawn into the defect. The excess penetrant is then removed from the surface while removing as little from the defect as possible. Penetrants may be visible in ambient light, or fluorescent, requiring the use of an ultraviolet light. The process using a visible liquid as penetrant is shown in Figure 4.33. A light coating of developer is then applied to the surface to draw up any penetrant trapped in the defect back to the surface again where it will be visible.
Product Quality
Published in G.K. Awari, C.S. Thorat, Vishwjeet Ambade, D.P. Kothari, Additive Manufacturing and 3D Printing Technology, 2021
G.K. Awari, C.S. Thorat, Vishwjeet Ambade, D.P. Kothari
Ultrasonic testing (UT) uses ultrasonic sound waves to penetrate a metal object, reflect off internal features, and bounce back to a detector to reveal the approximate size and location of these features. It generally relies on a liquid coupling between the probe and the top surface of the object. It may be limited by curved, complex internal and external surfaces, or the rough surfaces of AM deposited parts. Post-processing and finishing may be needed prior to the application of UT. Penetrant testing (PT) is often used to detect cracks or small surface breaking flaws. It uses a liquid penetrant, often a dye, sprayed on the surface to be tested, that is absorbed into the flaw features. The excess surface dye is wiped off and a liquid developer coating is sprayed on to dry and absorb penetrant from within the cracks, crevices, voids, or pores revealing the defect location (refer to Figure 10.7). While the method may be limited for use on as-deposited AM surfaces of powder-based systems, due to surface roughness, it can offer an effective method to detect cracks, lack of fusion, or undercuts in weld deposits of DED wire-based processes. Magnaflux testing is often used on large cast components to detect cracks in steel and other magnetic materials. It is often used to find cracks in engine components but may find application as applied to AM repaired parts.
Principles of Penetrants
Published in Don E. Bray, Roderic K. Stanley, Nondestructive Evaluation, 2018
Don E. Bray, Roderic K. Stanley
Penetrant inspection utilizes the natural accumulation of a fluid around a discontinuity to create a recognizable indication of a crack or other surface opening. Capillary action attracts the fluid to the discontinuity in a concentration heavier than in the surroundings. In order for the fluid concentration to be recognized, the background area must be of sufficient contrast to distinctly reveal the defect on the surface. The complete penetrant flaw detection system, therefore, consists of the fluid mechanics on the surface, as well as the recognition system that is used to detect the indication. A typical example of the principles involved in penetrant inspection is the ready visibility of cracks in concrete stabs shortly after a rain. After the sun has reappeared and the thinner surface water has evaporated, the heavier water concentration remaining around the cracks clearly reveals their location and shape.
Clean-integrity processing and characterization of nuclear-grade austenitic steel components
Published in Materials and Manufacturing Processes, 2023
M.K. Lei, S.H. Liu, J.Y. Gao, D.M. Guo
Figure 7 shows the coloration reaction photographs of the nuclear-grade AISI 316L austenitic stainless steel samples finished by grinding under a spindle speed of 1500 rpm and sequent polishing under 2000 rpm, respectively. The filter paper is dipped in the penetrant before the attachment on the finished surface of stainless steel samples. During the coloration reaction test, the white to orange-red color change is observed by attaching filter paper, which is proportional to [Fe(phen)3]2+.[4] The intensity of redness is dependent on the concentration of ferrous contaminants. The tiny orange-change degree is detected on the ground stainless steel samples by the two AISI 304 stainless steel wire brushes [Fig. 7(a,b)]. The red-colored filter paper is observed due to the embedded ferrous adhesives on the ground sample surface by the carbon spring steel wire brush [Fig. 7(c)]. The surface contaminants composition and microstructure are transferred from the carbon spring steel brush. No significant change is found by the combined processes of grinding and sequent polishing of the stainless steel samples [Fig. 7(d–f)]. The same phenomenon occurs on the finished sample surface by the stainless steel wire brushes and sequent flap discs, because the stainless steel wire brush and samples are the same Fe-Cr-Ni family stainless steel, leading to no significant contamination of heterogeneous compositions. The polishing process by flap discs effectively removes the overlaps transferred in the combined processes.